EXPLORING THE INFLUENCE OF SUNN HEMP AND NUTRIENT MANAGEMENT ON ORGANIC STRAWBERRY PRODUCTION AND FRUIT QUALITY

By

YURUI XIE

A THESIS PRESENTED TO THE GRADUATE SCHOOL

OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF

MASTER OF SCIENCE

UNIVERSITY OF FLORIDA

2016

© 2016 Yurui Xie

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To my Mom and Dad

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ACKNOWLEDGMENTS

I would like to thank my parents, my advisor Dr. Xin Zhao, my committee

member Dr. Charles A. Sims, Dr. Liwei Gu, and Dr. Jeffrey K. Brecht for their guidance

and financial support.

I would also like to thank Zack Black, Dustin M. Huff, Kim M. Cordasco, Sara M.

Marshall, Damian J. Graves, and all fellow colleagues in the lab for their support and

assistance.

This project was partially funded by a grant from the Walmart Foundation that

was administered by the University of Arkansas System Division of Agriculture Center

for Agricultural and Rural Sustainability.

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TABLE OF CONTENTS page

ACKNOWLEDGMENTS .................................................................................................. 4

LIST OF TABLES ............................................................................................................ 7

LIST OF FIGURES .......................................................................................................... 9

LIST OF ABBREVIATIONS ........................................................................................... 10

ABSTRACT ................................................................................................................... 11

CHAPTER

1 LITERATURE REVIEW .......................................................................................... 13

Strawberry Production ............................................................................................ 13

Growth in Organic Fruit Production ......................................................................... 13 Nutrient Management in Organic Strawberry Production ........................................ 14

2 INFLUENCE OF NUTRIENT MANAGEMENT INVOLVING SUNN HEMP ON ORGANIC STRAWBERRY PRODUCTION ............................................................ 17

Introduction ............................................................................................................. 17

Materials and Methods............................................................................................ 19

Experimental Design and Field Trial Establishment ......................................... 19

Soil and Plant Tissue Analyses ........................................................................ 22 Strawberry Plant Growth Assessment .............................................................. 23 Strawberry Fruit Yield Measurements .............................................................. 24

Statistical Analysis ............................................................................................ 24 Results and Discussion........................................................................................... 24

Soil and Plant Tissue Analyses ........................................................................ 24 Strawberry Plant Growth .................................................................................. 28 Strawberry Fruit Yield ....................................................................................... 30

Conclusions ............................................................................................................ 33

3 IMPACTS OF NUTRIENT MANAGEMENT INVOLVING SUNN HEMP ON ORGANIC STRAWBERRY FRUIT QUALITY ......................................................... 45

Introduction ............................................................................................................. 45

Materials and Methods............................................................................................ 48 Experimental Design and Field Trial Establishment ......................................... 48 Fruit Composition Analyses .............................................................................. 49 Quality Evaluation During Shelf Life ................................................................. 51 Consumer Sensory Analysis ............................................................................ 51 Statistical Analysis ............................................................................................ 52

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Results and Discussion........................................................................................... 52

Fruit Chemical Composition ............................................................................. 52 Quality Assessment During Shelf Life and Consumer Sensory Evaluation ...... 56

Conclusions ............................................................................................................ 57

4 INFLUENCE OF FERTILIZERS FROM DIFFERENT NITROGEN SOURCES ON STRAWBERRY GROWTH, YIELD AND QUALITY .......................................... 66

Introduction ............................................................................................................. 66 Materials and Methods............................................................................................ 69

Experimental Design and Greenhouse Strawberry Production ........................ 69 Soil and Tissue Analyses ................................................................................. 71 Plant Growth Assessment ................................................................................ 71

Strawberry Yield Evaluation ............................................................................. 72 Fruit Quality Evaluation .................................................................................... 72 Statistical Analysis ............................................................................................ 73

Results and Discussion........................................................................................... 73 Soil and Strawberry Leaf Tissue Analyses ....................................................... 73

Plant Growth ..................................................................................................... 74 Fruit Yield ......................................................................................................... 75 Fruit Quality ...................................................................................................... 77

Conclusions ............................................................................................................ 81

5 SUMMARY ............................................................................................................. 93

LIST OF REFERENCES ............................................................................................... 95

BIOGRAPHICAL SKETCH .......................................................................................... 109

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LIST OF TABLES

Table page 2-1 Fertilization rates of N, P, and K for treatments with different preplant

fertilization rates. ................................................................................................ 34

2-2 Soil organic matter, cation exchange capacity, and nutrient levels before sunn hemp incorporation (22 Sept. 2014) and at the end of strawberry season (29 Apr. 2015). ....................................................................................... 35

2-3 Nutrient management and cultivar effects on nutrient concentrations of most recently matured leaves at early season (26 Nov. 2014, 43 DAT) and after final harvest (22 Apr. 2015, 190 DAT). ............................................................... 36

2-4 Above- and below-ground biomass and estimation of total N, P, and K accumulation by strawberry plants. .................................................................... 37

2-5 Nutrient management and cultivar effects on leaf number, canopy size, crown diameter, and leaf chlorophyll content index of strawberry plants at early stage (14 Nov. and 4 Dec. 2014, 31 and 51 DAT), early and peak harvest (18 Dec. 2014 and 22 Jan. 2015, 65 and 100 DAT), and late season (12 Mar. and 22 Apr. 2015, 149 and 190 DAT)................................................... 38

2-6 Nutrient management and cultivar effects on total and marketable strawberry yields during the 2014-2015 production season in Citra, FL. .............................. 40

2-7 Nutrient management and cultivar effects on monthly marketable and total yields per plant during the 2014-2015 production season in Citra, FL. ............... 41

3-1 Nutrient management and cultivar effects on total soluble solids (TSS), titratable acidity (TA), pH, total monomeric anthocyanins (TMA), total phenolic content (TPC), and vitamin C (VC) of strawberry fruit from four harvests: 3 Jan. (81 DAT), 2 Feb. (111 DAT), 16 Mar. (153 DAT), and 30 Mar. 2015 (167 DAT) in the field trial at Citra, FL. .............................................. 59

3-2 Demographic information about consumers participating in sensory analysis of ‘Strawberry Festival’ fruit. ............................................................................... 60

3-3 Changes in strawberry fruit color during storage at 1˚C and 95% relative humidity. ............................................................................................................. 61

3-4 Consumer sensory ratingsz of strawberry fruit quality attributes for ‘Strawberry Festival’ grown under different nutrient management practices. ..... 62

3-5 Percentage distribution of panelists in sensory evaluation of strawberry fruit firmness levelz for ‘Strawberry Festival’ grown under different nutrient management practices on 30 Jan. 2015. ............................................................ 63

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4-1 Ingredients and N-P-K composition of three fertilizer treatments for in-season fertigation for strawberry production. .................................................................. 83

4-2 Fertilizer and cultivar effects on nutrient concentration of most recently mature leaves at early stage (26 DAT), middle season (76 DAT), and late season (171 DAT). ............................................................................................. 84

4-3 Fertilizer and cultivar effects on strawberry growth parameters at 25, 70, and 171 DAT throughout the production season. ...................................................... 85

4-4 Fertilizer and cultivar effects on total and marketable strawberry yields during the production season. ....................................................................................... 86

4-5 Fertilizer and cultivar effects on strawberry fruit color and firmness at 108, 130, 151 DAT (16 Feb., 10 Mar., and 31 Mar. 2015) throughout the production season. ............................................................................................. 87

4-6 Fertilizer and cultivar effects on strawberry compositional quality attributes at 104, 116, 131, 152 DAT (11 Feb., 23 Feb., 10 Mar., and 31 Mar. 2015) throughout the production season. ..................................................................... 88

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LIST OF FIGURES

Figure page 2-1 Daily soil temperature at the soil depth of 10 cm and precipitation between

sunn hemp incorporation and 4 weeks after strawberry transplanting. ............... 42

2-2 Cull fruit percentage (cull fruit weight per plant divided by total fruit weight per plant) during the during the 2014-2015 strawberry production season in Citra, FL. ...................................................................................................................... 43

3-1 Strawberry fruit fresh mass loss and external lightness change over time during storage at 1˚C and 95% relative humidity... ............................................. 64

3-2 Visual fruit quality ratings of strawberries and fruit firmness of ‘Strawberry Festival’ and ‘Camino Real’ during storage at 1˚C and 95% relative humidity. ... 65

4-1 Marketable and total fruit numbers of ‘Florida127’ and ‘FL 05-107’ by month during production season from Dec. 2014 to Apr. 2015. .................................... 89

4-2 Marketable and total fruit yields of ‘Florida127’ and ‘FL 05-107’ by month during production season from Dec. 2014 to Apr. 2015.. ................................... 90

4-3 Marketable and total fruit yields of three fertilizer treatments by month during production season from Dec. 2014 to Apr. 2015.. .............................................. 91

4-4 Classifications and percentage of strawberry cull fruit weight among all treatments during Dec. 2014 – Apr. 2015 production season.. ........................... 92

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LIST OF ABBREVIATIONS

DAT Days after transplanting

DOS Days of storage

HO Howard Organic treatment. Treatment that was fertigated with GATOR 96002/3-0-6 0-0 organic liquid in greenhouse study

MC Mayo Conventional treatment. Treatment that consists of Mayo fertilizer and potassium chloride, applied through fertigation in greenhouse study

NO Neptune Organic treatment. Treatment that consists of Neptune’s harvest fish fertilizer and potassium sulfate, applied through fertigation in greenhouse study

TA Titratable acidity

TMA Total monomeric anthocyanins

TPC Total phenolic content

TSS Total soluble solids

VC Vitamin C

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Abstract of Thesis Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Master of Science

EXPLORING THE INFLUENCE OF SUNN HEMP AND NUTRIENT MANAGEMENT ON

ORGANIC STRAWBERRY PRODUCTION AND FRUIT QUALITY

By

Yurui Xie

August 2016

Chair: Xin Zhao Major: Horticultural Sciences

Rotation with leguminous summer cover crop sunn hemp (Crotalaria juncea L.)

and fertilization with hydrolyzed fish and sodium nitrate based fertilizer products have

been employed by organic strawberry (Fragaria × ananassa Duch.) growers in Florida.

Integrating cover crops into strawberry nutrient management is often overlooked and

fertilizers derived from different nutrient sources differ in nitrogen release rate as well as

effects on soil biological activity. This research project consisted of a field trial and a

greenhouse experiment to explore the impact of different nutrient management

practices involving sunn hemp and organic fertilizers on organic strawberry production

and fruit quality. In the field trial, incorporation of sunn hemp residue into the soil with

full and reduced preplant N fertilization for the following strawberry crop was compared

with summer fallow control under organic production in terms of plant growth, yield, and

fruit quality, using two strawberry cultivars Strawberry Festival and Camino Real. In the

greenhouse experiment, two organic fertilizer treatments derived from hydrolyzed fish

and sodium nitrate, respectively, were assessed in comparison with a conventional

fertilizer treatment, with respect to their effects on strawberry plant growth, yield, and

fruit quality of SensationTM ‘Florida127’, and WinterstarTM ‘FL 05-107’. Overall, cultivar

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effects outweighed the nutrient management impacts on strawberry production and fruit

quality. Sunn hemp treatment with full preplant fertilization rate did not differ significantly

from the summer fallow control, while with reduced preplant fertilization rate the sunn

hemp treatment compromised early and total fruit yields. The fertilizer treatments

appeared to show greater impacts on fruit quality attributes, especially total soluble

solids and total phenolic contents, than their influence on strawberry plant growth and

fruit yield.

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CHAPTER 1 LITERATURE REVIEW

Strawberry Production

Strawberry (Fragaria × ananassa Duch.) has been cultivated worldwide as one of

the most valuable small fruit crops with a total production climbing from 5.04 to 7.74

million metric tons between 2003 and 2013 (FAOStat, 2015). The United States of

America is the second largest strawberry producer in the world, just behind mainland

China, followed by Spain, Turkey, and Mexico (FAOStat, 2015).

In 2014, the U.S. strawberry industry generated around 2.865 billion U.S. dollars,

which accounted for approximately 17.5% of the U.S. total value of non-citrus fruits

(USDA, 2015). As the second largest strawberry producing state behind California,

Florida produced 103,600 metric tons of strawberries in 2014, with a value of $306

million, or 75.9% of the Florida total non-citrus fruits value (USDA, 2015).

Growth in Organic Fruit Production

Organic foods have gained popularity among consumers as a result of

environmental concerns and human health consciousness (Batte et al., 2007;

Thompson 1998) despite commanding a premium price over conventional foods

(Oberholtzer et al., 2005). The interest in organic farming is also increasing among

growers in Florida as shown by increased acreage of total certified and exempt organic

land between 2008 and 2014 (USDA, 2010; USDA, 2016). Among all the organically

grown foods, fresh fruits and vegetables are the top-selling commodities and sales

amounts have continued rising in recent years (Dimitri and Greene, 2000). California

and Washington State are the top organic fruit production states with U.S. leading

production values for grape, apple, pear, and sweet cherry; Florida and Oregon are the

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next leading organic fruit producers (USDA, 2013 a). California dominates organic fruit

production due to its heavy concentration on strawberry.

While the majority of the U.S. strawberry production is conventional, consumer

demand for organic strawberries has been increasing in recent years, and interest in

organic strawberry production is growing among producers. By 2011, certified organic

farm acreage for berries reached 2,575 acres in Florida, or 16.7%, of the state total of

15,394 acres of certified organic fruit farms (USDA, 2013 b). There were 14,093

certified or exempt organic farms, or 3,670,560 acres, in the United States, and 166

organic farms or 19,364 acres established in Florida as of 2014 (USDA, 2016). From a

national perspective, organic strawberry shared more than half of total sales for organic

small fruits, or 54%; harvested acreage increased by 4% while total gross value of sales

climbed by 52%, even though the harvested quantity decreased by 11% from 2008 to

2011 (Perez and Plattner, 2013).

Nutrient Management in Organic Strawberry Production

Nutrient management for production of organic crops including strawberry has

been a hot topic in recent years. Cover crop rotation has been widely adopted in organic

growing systems as a nutrient management practice. The benefits of using cover crops

in farming systems, including weed suppression, pest and disease management, soil

organic matter improvement, and soil compaction and erosion reduction, have long

been recognized (Hartwig and Ammon 2002; Sarrantonio and Gallandt, 2003). Non-

leguminous cover crops help better conserve soil nitrogen (N) from leaching while

leguminous cover crops also fix atmospheric N and lead to increased N availability for

succeeding crops (Hoyt and Hargrove, 1986; Smith et al., 1987). Cover crop

incorporation into soil speeded up plant material decomposition and N release as a

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result of increased microbial activity and balanced temperature and water regimes

compared with no tillage (Schomberg et al., 1994). Cover crop decomposition and N

mineralization are highly related to plant residue properties [e.g., Carbon (C):N ratio],

management practices (e.g., tillage) as well as environmental conditions (e.g., soil

temperature and moisture) (Robertson and Groffman, 2007; USDA Natural Resources

Conservation Service, 2011). Therefore, the differences in availability of nutrients from

cover crop residue might lead to variations in subsequent crop performance.

Summer cover crops can produce a range of 2,000-10,000 kg/ha biomass with

23-168 kg/ha N annually depending on the crop type and cultivar (Newman et al.,

2007). Rotation with winter hairy vetch (Vicia villosa Roth.), Austrian winter pea (Pisum

sativum L.), or crimson clover (Trifolium incarnatum L.) resulted in greater grain yields of

the following corn (Zea mays L.) crop than no cover crop control at zero N fertilization

(Decker et al., 1994). Winter hairy vetch alone or with rye (Secale cereale L.) was

reported to provide abundant N for the following sweetcorn crop and led to maximum

sweetcorn yields (Cline and Silvernail, 2002). In addition, winter hairy vetch residue was

also reported to increase corn yield and N uptake at zero N fertilization (Kuo and

Jellum., 2002). Both warm- and cool- season cover crops are capable of retaining soil N

and reducing N loss (Dabney et al., 2001; MacDonald et al. 2005; O’Connell et al.,

2015). However, around 50% of N was lost in 4 weeks after sunn hemp (Crotalaria

juncea L.) incorporation under Florida sandy soil conditions (Cherr et al., 2006).

Compost amended into the soil was shown to enhance strawberry plant growth

and fruit quality by promoting plant biomass and leaf chlorophyll content, as well as

elevating levels of fruit organic acids and sugars (Wang and Lin, 2002). Preplant

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fertilization, which provides adequate macronutrients for strawberry establishment, is

commonly practiced in strawberry production. Amending N for strawberry in the early

season not only promoted vegetative growth of the plants, but was also shown to

increase fruit yield in the following spring (Strik et al., 2004). However, with the sandy

soils in Florida with their poor water and nutrient holding capacity, the potential benefits

of preplant fertilization may be questionable. As for in-season fertilization, excess N may

affect fruit quality adversely by reducing fruit soluble solids (Cantliffe et al., 2007), while

K may be favorable for fruit quality development. Existing research data indicates that

an average of 40 to 60% of crop yield is due to fertilizer nutrient inputs in the U.S.

(Stewart et al., 2005). Organic fertilizers and amendments from different nutrient

sources may differ in nutrient composition, form, and availability, thus resulting in

diverse effects on plant growth, fruit yield and quality.

Better understanding of N dynamics between release from cover crop residue

and uptake by cash crops is needed for optimizing nutrient cycling in organic production

systems. Nutrient management of short-day strawberry as grown in Florida and its

effects on strawberry growth, yield, and fruit quality are the focus of this thesis study.

The goal was to explore a more nutrient-efficient management practice for organic

strawberry production while maintaining and improving fruit yield and quality.

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CHAPTER 2 INFLUENCE OF NUTRIENT MANAGEMENT INVOLVING SUNN HEMP ON ORGANIC

STRAWBERRY PRODUCTION

Introduction

Strawberry as one of the most valuable small fruit crops in the United States,

accounted for approximately 17.5% of the total value of non-citrus fruits in 2014, with a

production area over 24,800 hectares and a production value of $2.865 billion (USDA,

2015). Florida is a leading state in winter strawberry production focused on the high-

value early market. The $306 million Florida strawberry industry produced over 105,200

tons of strawberries on approximately 4,450 hectares in 2014 (USDA, 2015). Although

the organic strawberry acreage was only about 5% of the total U.S. strawberry

production in 2014, harvested acreage and sales value of organic strawberries

increased by approximately 89% and 104%, respectively, between 2008 and 2014

(USDA, 2010; USDA, 2016). Growers’ interest in organic strawberry production is also

growing in Florida as shown by the increase in number of certified and exempt organic

farms according to the recent U.S. organic production surveys (USDA, 2010; USDA,

2016).

Cover crops are an essential part of the soil quality and fertility management

program in organic crop production systems. Appropriate use of cover crops helps

improve soil organic matter and health, reduce soil compaction and erosion, and

suppress weeds. Leguminous cover crops are also employed as green manure

contributing to increased N availability (Muramoto et al., 2011; Parr et al., 2014).

Integration of cover crop residue into nutrient management programs for organic crop

production promotes nutrient cycling and helps optimize the benefits of using rotational

cover crops. Ebelhar et al. (1984) reported that an estimation of 90–100 kg/ha of

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equivalent N could be supplied annually by the winter legume cover crop hairy vetch to

no-tillage corn. Different legumes and grass species not only differ in biomass

accumulation, but also vary in N release rate (Ranells and Wagger, 1996). In addition to

environmental factors such as soil temperature and moisture, the rate of N

mineralization and release from cover crop residue is largely determined by the

carbon:nitrogen (C:N) ratio of the cover crop at termination. A C:N ratio near 24:1

facilitates microbial digestion to achieve relatively fast breakdown of plant residue,

whereas greater C:N may result in temporary N deficit to the following crop due to N

immobilization (Ozores-Hampton, 2012; USDA Natural Resources Conservation

Service, 2011). On the other hand, a C:N lower than 24:1 may speed up N release early

in the season, making it difficult to meet crop nutrient demand during yield development.

Growing cover crops prior to the strawberry season has been shown to be an

effective tool for weed management, but previous studies yielded mixed results

regarding the cover crop effects on growth and yield of strawberry. Garland et al. (2011)

found that sudangrass (Sorghum bicolor L.), pearl millet (Pennisetum glaucum L.),

soybean (Glycine max L.), or velvetbean [Mucuna deeringiana (Bort) Merr.] suppressed

summer weed population with no effect on organic strawberry growth or yield in North

Carolina when two short-day strawberry cultivars were planted in the fall. However, a

study conducted in Iowa indicated that sudangrass, big bluestem (Andropogon gerardii

Vitman), or switchgrass (Panicum virgatum L.) grown and incorporated into the soil in

summer before strawberry planting not only reduced fall weed population and biomass,

but also improved plant establishment and increased fruit yield of the following

conventional short-day strawberry crop (Portz et al., 2011).

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In Florida, summer cover crops have been used in rotation with fall planting of

strawberry by organic growers, with sunn hemp as the most commonly used cover crop

owing to its suppressive effects on sting nematode (Belonolaimus longicaudatus Rau.),

a major pest in Florida strawberry production (Noling, 2015). Sunn hemp can produce

5,050–11,235 kg/ha dry biomass with 2.85% N in plant material, and provide 100–200

kg/ha of total available N to the subsequent cash crop (Li et al., 2009; Newman et al.,

2010; Schomberg et al., 2007). Sunn hemp was considered a well-suited cover crop in

the Southeastern U.S. capable of providing 33–50% of total N needed for most crops,

assuming 50% availability of N accumulated from sunn hemp after 60 days of seeding

(Schomberg et al., 2007). However, despite the popularity of using sunn hemp in

rotation with organic strawberry cultivation, research-based information is not currently

available regarding the impact of sunn hemp on plant performance of the following

strawberry crop as well as the role of sunn hemp in nutrient management of organic

strawberry given its considerable contribution of N release.

In this study, the effects of sunn hemp as a summer rotational crop and

modification of nutrient management for the subsequent strawberry crop by estimating

the nutrient availability from sunn hemp biomass accumulation were assessed in terms

of plant growth and fruit yield of two strawberry cultivars in an organic production

system.

Materials and Methods

Experimental Design and Field Trial Establishment

The field trial was conducted during the 2014–2015 strawberry season on

certified organic land at the University of Florida Plant Science Research and Education

Unit in Citra, FL (lat. 29.41˚N, long. 82.16˚W). The soil at the experimental site is

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classified as Candler sand, which is from Eolian deposits and sandy and loamy marine

deposits. Sunn hemp was planted at a seeding rate of 44.8 kg/ha on 17 July 2014. The

plants were later incorporated into the soil by flail mowing and roto-tilling at a depth of

12.7 cm on 22 Sept. 2014, at which time < 5% plants had started to flower. The plots

were tilled twice more at 12.7 cm depth before bed formation and strawberry

transplanting on 14 Oct. 2014. The without sunn hemp plots were maintained as

summer fallow before strawberry planting. In order to minimize the weed pressure effect

on the study, summer fallow plots were tilled three times at a soil depth of approximately

12.7 cm on 13 Aug., 7 Sept., and 14 Oct. 2014. All the field plots were hand-weeded

during the strawberry season.

The field experiment was arranged in a split plot design with 4 replications and

80 plants per plot. Nutrient management practice for organic strawberry production was

the whole plot factor, while strawberry cultivar was the subplot factor. There were three

nutrient management treatments in the whole plots which were randomized in a

complete block design, including: 1). sunn hemp as a summer cover crop before

strawberry planting with preplant N fertilizer applied at the rate of 84.0 kg/ha (full rate);

2). sunn hemp as a summer cover crop before strawberry planting with a reduced

preplant N fertilizer application rate at 19.8 kg/ha, assuming 50% of the N from sunn

hemp biomass would be available for uptake by strawberry plants following the sunn

hemp residue incorporation, with calculations based on sunn hemp biomass estimation

and tissue analysis for nutrients (reduced rate); and 3) summer fallow control without

sunn hemp and with the full preplant application rate of N fertilizer at 84.0 kg/ha. The full

rate preplant fertilization of N (84.0 kg/ha) was determined based on the

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recommendation of total N fertilization of 168 kg/ha for strawberry production in Florida

with preplant application of N at 0-44.8 kg/ha included (Santos et al., 2012), taking into

consideration the nutrient availability from organic fertilization during the production

season. Preplant fertilization with phosphorus (P) and potassium (K) was also done

based on the soil test results. For the reduced preplant fertilization treatment, P and K

availability from sunn hemp residue was factored into the calculation. Sunn hemp was

sampled for above- and below-ground biomass accumulation and nutrient composition

analysis (Waters Agricultural Laboratories, Inc., Camilla, GA) in 5 randomly selected

areas for each sunn hemp plot using 0.5 m x 0.5 m quadrants. After drying the fresh

tissue at 65˚C for 2 weeks to constant weight, the total amount of dry weight of sunn

hemp residue was estimated and used for determination of the total amounts of N, P,

and K provided by sunn hemp based on the corresponding tissue nutrient analysis

results. The organic fertilizers used for preplant application included a mixture of

MicroSTART60 3N-0.9P-2.5K (Perdue AgriRecycle, LLC., Seaford, DE), Howard

Organic Bonemeal 7N-5.2P-0K (Howard Fertilizer & Chemical Co., Inc., Orlando, FL),

and Jobe’s Organics Bone Meal 2N-6.1P-0K (Easy Gardener Products, Inc., Waco, TX).

GATOR 96002 Organic Liquid 3N-0P-5.0K (Howard Fertilizer & Chemical Co., Inc.,

Orlando, FL) was used for in-season fertigation through drip irrigation. All the fertilizer

products are approved for use in certified organic crop production. The preplant

application rates of N, P, and K as well as the application rates throughout the whole

season of strawberry production are presented in Table 2-1. Two strawberry cultivars,

Camino Real and Strawberry Festival, were used in this study. Both are short-day

cultivars and have been used by organic strawberry growers in Florida.

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Strawberry plug plants (Luc Lareault Nursery, Quebec, Canada) were

transplanted into double rows spaced 30.5 cm apart on the raised beds on 14 Oct.

2014. The planting beds were 81.0 cm wide at the base and 71.0 cm wide at the top,

17.8 cm high, and spaced 152.4 cm apart on centers. The beds were covered by 1.25

mil black polyethylene mulch (Intergro, Inc., Clearwater, FL). Timer controlled irrigation

was applied twice per day, for 45 min each event, and adjusted as needed. Plants were

fertigated through a drip irrigation system under the plastic mulch at the N application

rate of 0.67 kg/ha/day starting from 14 Nov. 2014, and increased to 1.12 kg/ha/day from

5 Dec. 2014, and finally adjusted to 1.34 kg/ha/day from 6 Mar. 2015 until the end of

season. AgroFabric Pro42 row covers (Universal Enterprises Supply, Pompano Beach,

FL) were applied for frost protection. The predatory mites Phytoseiulus persimilis and

Neoseiulus californicus (Spidex and Spical; Koppert Biological Systems, Inc., Howell,

MI) were released to control twospotted spider mites on 21 Nov. 2014.

Soil and Plant Tissue Analyses

Soil samples were collected at a depth of 30 cm for nutrient analysis before sunn

hemp incorporation (22 Sept. 2014) and at the end of strawberry season (29 Apr. 2015).

The soil sampling before sunn hemp incorporation was made up of 3 samples from

each nutrient management treatment plot in each block/replication, and the soil

sampling at the end of strawberry season was composed of composite samples from

each of the experimental plots. Soil organic matter, cation exchange capacity (CEC),

total soil N, and levels of P, K, Calcium (Ca), Magnesium (Mg), Sulfur (S), Copper (Cu),

Iron (Fe), Manganese (Mn), Zinc (Zn), and Boron (B) were analyzed. The soil test

results obtained before strawberry planting were used to develop the soil fertility

management program for the strawberry season.

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Strawberry tissue analyses were conducted at early season [26 Nov. 2014, 43

days after transplanting (DAT)] and after final harvest (22 Apr. 2015, 190 DAT) by

sampling 14 of the most recently matured leaves in each plot. Soil and plant tissue

analyses, as well as a nematode assay at the end of the season, were performed by

Waters Agricultural Laboratories, Inc., Camilla, GA.

Strawberry Plant Growth Assessment

Plants with open flowers were counted on 4 Nov., 10 Nov., 17 Nov., and 2 Dec.

2014. Four randomly selected strawberry plants from each plot were marked on 14 Nov.

2014 for growth assessments including leaf number, canopy size, and crown diameter

at early stage (14 Nov. and 4 Dec. 2014, 31 and 51 DAT), early and peak harvest (18

Dec. 2014 and 22 Jan. 2015, 65 and 100 DAT), and late season (12 Mar. and 22 Apr.

2015, 149 and 190 DAT), respectively. Leaf chlorophyll content index was examined at

31, 51, 65, and 190 DAT on 10 fully matured leaves in each plot using a SPAD 502 Plus

Chlorophyll Meter (Spectrum Technologies, Inc., Aurora, IL). Only the leaves emerged

after transplanting were counted. The narrowest and widest canopy diameters were

measured and the average of the two measured diameters was used to determine the

canopy size. Crown diameter was measured using an electronic caliper. The above-

and below-ground biomass of strawberry plants excluding flowers or fruit was assessed

on 1 May 2015 after the final harvest. Three randomly selected plants from each

treatment per replication were collected from the field, cleaned, separated at the soil

line, and oven-dried at 60˚C for 4 weeks to constant weight. The dry samples were then

weighed to estimate plant biomass accumulation over the whole season.

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Strawberry Fruit Yield Measurements

Fruit with calyces attached were picked from all field plots. Strawberry harvests

were performed during 4 Dec. 2014 to 6 Apr. 2015, around twice a week, and a total of

26 harvests were achieved during the production season. Marketable and unmarketable

yields as well as numbers of marketable and unmarketable berries were measured.

Strawberry fruit (> 5 g) with red color over at least 80% of the surface area, and without

decay, disease, pest, or mechanical damages, were harvested as marketable yield.

Unmarketable fruit were categorized as deformed, small, damaged (due to pests,

rodents, and rain), rot (caused by botrytis, anthracnose, leather rot, or soft rot), and

other. Cull fruit numbers of each category were also recorded.

Statistical Analysis

Data analysis was performed using the Glimmix procedure of the SAS statistical

software package for Windows (Version 9.2; SAS Institute, Cary, N.C.). Two-way

analysis of variance (ANOVA) following the split plot design used was conducted.

Fisher’s Least Significant Difference (LSD) test was used for multiple comparisons of

different measurements among treatments at α = 0.05.

Results and Discussion

Soil and Plant Tissue Analyses

The soil test before sunn hemp incorporation showed that soil organic matter,

CEC, total soil N, as well as available soil P, Ca, Mg, S, Fe, Mn, Zn, Cu, and B did not

differ significantly between the summer fallow field plots and those planted with sunn

hemp during the same period, while summer fallow plots had higher available soil K

content than sunn hemp plots with full or reduced preplant fertilization (Table 2-2). At

the end of the strawberry production season, similar levels of soil organic matter, CEC,

25

and most of the available soil nutrients were observed among soil management

practices; however, field plots with sunn hemp grown as a summer rotational crop

exhibited a significantly lower level of total soil N compared with the plots without sunn

hemp. Interestingly, the total soil N level was similar in the full and reduced fertilization

rate plots with sunn hemp. The ‘Camino Real’ plots showed a significantly higher level

of soil available K than the ‘Strawberry Festival’ plots (Table 2-2), suggesting a possible

higher demand of K by ‘Strawberry Festival’. Sting nematode infestation did not interfere

with the treatments in this study as soil tests of each plot at the end of season showed

an undetectable level of sting nematode population.

Sainju et al. (2002) reported that incorporating hairy vetch grown during the fall

and winter into the soil prior to spring planting of tomato (Lycopersicon esculentum Mill.)

did not affect soil organic C but increased soil organic N at the end of tomato

production, in comparison with incorporation of winter weeds. Moreover, soil organic C

was not impacted by in-season N fertilization rate while soil organic N was found

highest at the full application rate of N compared with the reduced N rate. In the present

study, sunn hemp produced an average amount of dry biomass of 4,617 kg/ha, which

contained approximately 117 kg of N. The average C:N ratio of sunn hemp residue at

termination was about 21:1, suggesting that a relatively fast decomposition might have

occurred during the early season of strawberry production (Li et al., 2009; Newman et

al., 2010; Schomberg et al., 2007). Daily average soil temperature at 10 cm depth

ranged from 13.5 to 28.3˚C whereas heavy rainfall occurred between sunn hemp

termination (22 Sept. 2014) and 4 weeks after strawberry transplanting (14 Oct. 2014)

(Figure 2-1). Nitrogen mineralization and release from organic amendments is strongly

26

correlated with soil temperature and moisture, being generally faster in warmer and

moist soils until soil water potential reaches its maximum (Agehara and Warncke, 2005;

Cabrera et al., 2005; Fan and Li, 2010; O’Connell et al., 2015; Quemada and Cabrera,

1997). Given that the active plant uptake of nutrients, particularly N, may not take place

until field establishment of the strawberry crop (i.e., at least 7-10 DAT), it was likely that

some of the mineralized N from sunn hemp residue at the beginning of strawberry

production was lost from the root zone. Previous research by Cherr et al. (2006)

showed that around 50% of N was lost in 4 weeks after sunn hemp incorporation under

Florida sandy soil conditions. Warm-season cover crops were shown to help better

conserve soil N than bare ground after heavy precipitation events (O’Connell et al.,

2015), while in this study, despite the potential N loss, tilling the soil and incorporating

the summer weeds into the soil twice in the summer fallow plots during the sunn hemp

growing period might result in higher inorganic N level due to the stimulated soil

microbial activity (Havlin et al., 1990; Salinas-Garcia et al., 1997; Sainju et al., 2002).

Soil nutrient levels were not monitored between sunn hemp termination and the final

strawberry harvest in this study. Future research will need to assess the soil nutrient

(especially N) status during the entire season to obtain a better understanding of soil

nutrient dynamics as affected by sunn hemp incorporation and preplant fertilization.

With respect to the strawberry leaf tissue nutrient composition during the early

season (26 Nov. 2014, 43 DAT) and after the final harvest (22 Apr. 2014, 191 DAT),

overall it was not significantly affected by the nutrient management practice treatments

except for Mn and S. Leaf Mn showed a significantly higher level in the sunn hemp

treatment with reduced preplant fertilization than the full rate sunn hemp treatment and

27

summer fallow control, while the summer fallow control exhibited a higher concentration

of S than the sunn hemp treatments. By contrast, strawberry cultivar had a greater

impact on leaf nutrient concentration, while the varietal difference varied during the

production season (Table 2-3). The leaf tissue concentrations of P, Cu, and Zn were

significantly higher in ‘Camino Real’ than ‘Strawberry Festival’ in the early season,

whereas ‘Strawberry Festival’ had higher levels of leaf P, Mg, Fe, Mn, and B after the

final harvest (Table 2-3). Nutriment management by cultivar interaction was detected in

Zn at early season as shown by the higher level of Zn in the summer fallow control in

‘Camino Real’ but not in ‘Strawberry Festival’ (Data not shown). The interaction effects

were also found in P, S, and B concentrations during the late season. ‘Strawberry

Festival’ grown with reduced preplant fertilization had significantly lower levels of P and

S compared with the other two nutrient management practices, while sunn hemp with

full preplant fertilization resulted in highest B concentration in ‘Strawberry Festival’ but

lowest B level in ‘Camino Real’ (Data not shown). The strawberry leaf tissue analysis in

the early season indicated that regardless of the nutrient management practice and

strawberry cultivar, plants were adequate in N, K, Ca, S, B, Mn, and Fe, high in P and

Mg, but slightly deficient in Zn and Cu, according to Santos et al. (2012). Concentrations

of most nutrients in the leaf tissue decreased or remained at similar levels between the

early season and after final harvest, while increased levels of K, Zn, and Cu level were

observed (Table 2-3). Estimation of total nutrient accumulation in leaf tissue collected

after final harvest showed a significant reduction of N, P, and K in plants grown in the

sunn hemp plots with reduced preplant N fertilization in contrast to the full rate sunn

28

hemp plots and the summer fallow control, whereas no difference was observed

between the two strawberry cultivars (Table 2-4).

Although the leaf tissue nutrient concentration was not markedly influenced by

sunn hemp, the lower level (reduced fertilization rate) or similar level (full fertilization

rate) of nutrient accumulation in above-ground biomass after final harvest of strawberry

in the sunn hemp treatments compared with the summer fallow control indicated limited

nutrient contribution from the sunn hemp residue to the strawberry crop over a long

production period of over 5 months (Table 2-4). Using fall cover crop rotation was found

to promote soil inorganic N level in the spring season (Möller et al., 2008), while Kuo

and Jellum (2002) observed similar N uptake by corn with zero N fertilization between

winter legume/grass cover cropping and no cover crop control. Our findings suggested

that the role of sunn hemp in increasing soil N might be restricted owing to the warm

humid conditions at sunn hemp termination and the early season of strawberry

production. Flail mowing sunn hemp might also have accelerated decomposition of

plant residue, resulting in N loss prior to acquisition by strawberry plants.

Strawberry Plant Growth

The reduced preplant fertilization with incorporation of sunn hemp resulted in

fewer leaves and smaller crown than in the full N fertilization treatment and the summer

fallow control at 31 DAT (14 Nov. 2014) (Table 2-5). Within the sunn hemp treatments,

the canopy size was also smaller in the reduced fertilization plot, but it did not differ

significantly from the without sunn hemp control (Table 2-5). The leaf number and crown

diameter remained lower in the reduced fertilization treatment than the full rate sunn

hemp treatment at 51 DAT (4 Dec. 2014) (Table 2-5). ‘Strawberry Festival’ consistently

had greater numbers of leaves than ‘Camino Real’ at each sampling between 31 to 100

29

DAT (14 Nov. 2014–22 Jan. 2015). Larger canopy (65 and 100 DAT, 18 Dec. 2014–22

Jan. 2015) and crown diameter (100 DAT, 22 Jan. 2015) were also observed in

‘Strawberry Festival’, whereas leaf chlorophyll content index was significantly lower in

‘Strawberry Festival’ at 51 DAT (4 Dec. 2014) (Table 2-5). As expected, ‘Camino Real’

had fewer plants with open flowers than ‘Strawberry Festival’ with regards to early-

season flower count (data not shown). Moreover, ‘Strawberry Festival’ grown in the

reduced preplant fertilization treatment exhibited significantly fewer plants with open

flowers than the full rate sunn hemp treatment and the summer fallow control (Data not

shown). Above-ground biomass assessment after the final harvest revealed a significant

reduction in the sunn hemp treatment with reduced preplant fertilization in comparison

with the full rate sunn hemp treatment and the summer fallow control (Table 2-4).

These results indicated that reducing preplant fertilization (from 84.0 to 19.8 kg

N/ha) in the sunn hemp treatment compromised early growth and development of

strawberry plants. Without modifying the fertilization program for the strawberry crop,

growing sunn hemp as a summer rotational cover crop did not demonstrate any effects

in terms of promoting the growth of strawberry plants. Schomberg et al. (2007) pointed

out that maximum biomass (8,900–1,3000 kg/ha) of sunn hemp at a seeding rate of 13

kg/ha (planted in rows) and 90-day growth period was produced during Apr. and May in

the Southeastern costal area, which provided 135–285 ka/ha N. In our study, sunn

hemp produced much less dry matter (4,617 kg/ha) with much higher seeding rate (44.8

kg/ha) but a shorter growing period of 67 days compared with the results of Schomberg

et al. (2007). Relatively high seeding rate was used here for weed suppression, while

future studies need to investigate the sunn hemp planting systems in order to optimize

30

N output from sunn hemp. Rapid N loss from soil in rainy summer season in Florida

might be another reason that sunn hemp residue did not improve strawberry growth in

this study. Cherr et al. (2006) reported similar maximum biomass and N accumulation

(12,200 and 172 kg/ha) of sunn hemp after a 98-day establishment as Schomberg et al.

(2007), but also observed substantial N loss after sunn hemp termination, which

resulted in reduced N availability to subsequent winter corn under sandy soil condition

in Florida.

Strawberry Fruit Yield

Strawberry cultivar and nutrient management practices affected the full-season

fruit yields (Table 2-6). ‘Strawberry Festival’ had more marketable and total fruit number

per plant as well as higher total marketable yield than ‘Camino Real’, whereas ‘Camino

Real’ exhibited larger fruit size as shown by the greater average marketable fruit weight

(Table 2-6). There were no significant differences between the sunn hemp treatment

with full preplant N fertilization and summer fallow control, while the sunn hemp

treatment with reduced preplant N fertilization led to significantly lower total fruit number

and yield (Table 2-6). However, marketable fruit number and yield and average weight

of marketable fruit did not differ significantly among the nutrient management practices

(Table 2-6). On a monthly basis, total and marketable yield and fruit numbers were

consistently higher during Dec. 2014–Feb. 2015 for ‘Strawberry Festival’ compared with

‘Camino Real’ except for the similar total fruit yield in both cultivars in Jan. 2015 (Table

2-7). ‘Camino Real’ produced higher total fruit yield but fewer total fruit number than

‘Strawberry Festival’ in Mar. and Apr. 2015 (Table 2-7). Surprisingly, compared with the

two sunn hemp treatments, the summer fallow control showed significantly higher total

and marketable fruit numbers and yields in Dec. 2014 as well as higher total fruit

31

number in Mar. and Apr. 2015 and higher total fruit yield from Dec. 2014 to Feb. 2015.

Interestingly, there were no significant differences between the sunn hemp treatments

with different preplant fertilization rates (Table 2-7). As for unmarketable fruit yield

throughout the season, ‘Camino Real’ had higher cull yield percentage than ‘Strawberry

Festival’ while no differences were observed among nutrient management practices

(Figure 2-2). In addition, botrytis and pest damage were the main causes of

unmarketable yield; anthracnose incidence tended to be lower in ‘Strawberry Festival’

grown in the sunn hemp treatment with reduced preplant N fertilization than in the full

rate sunn hemp treatment and the summer fallow control (Figure 2-3).

The results indicated that cultivar differences outweighed the effects of nutrient

management on both the full-season yield and monthly yield components of organically

grown strawberry in the present study. Overall, ‘Strawberry Festival’ showed better yield

performance than ‘Camino Real’. Although the full-season marketable yield was not

affected by sunn hemp treatments, the reduced early marketable yield and total fruit

yield during the production season in the sunn hemp plots, especially with reduced

preplant fertilization, indicated that relying on the N release from sunn hemp to

supplement preplant fertilization might not be feasible for maintaining early fruit yield of

strawberry plants. Similarly, sunn hemp residue with 200 kg N/ha full-season fertilization

was reported not to benefit tomato yield in comparison with conventional summer fallow

until the third year; yields of following tomato and pepper (Capsicum annum L.) were

higher than summer fallow treatment after 3 years (Avila et al., 2006). Therefore, long-

term effects of sunn hemp rotation with strawberry need to be addressed in the future

as well. Sunn hemp residue management might not be optimal in this study, which likely

32

resulted in more N loss during the early season of strawberry production. The summer

fallow plots were subject to tillage for weed control during the summer period in order to

minimize the weed pressure impact in this study focused on nutrient management.

Summer fallow with rototilling twice before bell pepper production resulted in greater

nutsedge (Cyperus spp.) suppression compared with no tilling control (Miller et al.,

2014). It would be interesting to explore the summer fallow tillage effects on nutrient

availability and early strawberry crop performance in sandy soils. The strawberry

marketable yield in the current study was relatively low as a result of high cull

percentage. Low yield in the current study might be related to consecutive frost events

in the winter: 19-30 Oct., 19-20 Nov., 10-16 Dec., 2014 and 28-29 Jan., 19-21 Feb.,

2015 (FAWN, 2016), which resulted in marketable yield reduction as a result of

extended frost protection by row cover.

In general, preplant N fertilization is beneficial for crop establishment and yield

performance. Vetsch and Randall (2002) found that corn grain yield was increased by

starter fertilizer in all tillage systems, while similar yield increase effects with N starter

fertilizer were observed in soybean (Osborne and Riedell, 2006; Touchton and Rickerl,

1986). However, the effects of preplant N application were absent or minimal in several

Florida strawberry studies. Santos and Whidden (2007) reported that there was no

difference in either monthly or total strawberry yield between preplant N fertilization at

the rate of 56 kg/ha and the control without preplant N application. Cantliffe et al. (2007)

suggested that no differences in either early or total marketable strawberry yields were

found among different N levels for whole season when grown in soilless media coconut

coir and pine bark. However, also in Florida, Santos (2010) and Santos and Ramirez-

33

Sanchez (2009) found that preplant N fertilizer at 56 kg/ha N containing 30-64 kg/ha S

might help increase both early and total marketable strawberry yields. Therefore, S

accumulation of sunn hemp is another point to consider in the future.

Conclusions

In this study, growing sunn hemp as a summer rotational crop did not show any

growth or yield improvement effects on winter production of strawberry in sandy soils.

Decreasing preplant N fertilization rate by taking into consideration the nutrients,

particularly N, provided by soil incorporation of sunn hemp residue reduced early and

total fruit yields, suggesting that the nutrient contribution by sunn hemp to strawberry

yield performance might be limited. The influence of nutrient management did not vary

with strawberry cultivar used, and overall ‘Strawberry Festival’ was shown to be a better

yielding cultivar than ‘Camino Real’ under organic production in this study. Given the

environmental impact of cover crop residue decomposition and nutrient release, long-

term studies are needed to better understand the soil nutrient dynamics and strawberry

plant nutrient uptake as affected by sunn hemp residue. Sunn hemp cropping systems

and termination methods may be improved to help match cover crop nutrient release

with the subsequent strawberry crop needs for better crop establishment and fruit yield

development.

34

Table 2-1. Fertilization rates of N, P, and K for treatments with different preplant fertilization rates.

N

(kg/ha) P

(kg/ha) K

(kg/ha) Ingredients and ratio

Pre-plant fertilization

Full N rate 84.0 45.5 21.4 MicroSTART60: Howard Organic Bonemeal = 3:2

Reduced N rate 19.8 38.8 5.6 Jobe’s Organics Bone Meal: MicroSTART60 = 2:1

In-season fertigation 152.2 0.0 253.6 GATOR 96002/3-0-6 Organic

Whole season fertilization Full N rate 236.2 45.5 275.0 Reduced N rate 172.0 38.8 259.2

35

Table 2-2. Soil organic matter, cation exchange capacity, and nutrient levels before sunn hemp incorporation (22 Sept. 2014) and at the end of strawberry season (29 Apr. 2015).

Before sunn hemp incorporation

Treatment

OM CEC TN P K Ca Mg S Fe Mn Zn Cu B

(%) (meq/ 100g) (%) (kg/ha) (kg/ha) (kg/ha) (kg/ha) (kg/ha) (kg/ha) (kg/ha) (kg/ha) (kg/ha) (kg/ha)

Management SF w/ full N 0.77 3.76 0.04 81 24az 1016 125 39 18 3 0.66 0.27 0.26 SH w/ full N 0.76 3.66 0.05 81 20b 1033 119 25 21 3 0.63 0.27 0.23 SH w/ reduced N 0.79 3.82 0.07 78 20b 1056 120 26 19 3 0.76 0.30 0.25

Significancey NS NS NS NS * NS NS NS NS NS NS NS NS

At the end of strawberry season Treatment OM CEC TN P K Ca Mg S Fe Mn Zn Cu B

Management (%) (meq/ 100g) (%) (kg/ha) (kg/ha) (kg/ha) (kg/ha) (kg/ha) (kg/ha) (kg/ha) (kg/ha) (kg/ha) (kg/ha)

SF w/ full N 0.67 4.54 0.19a 113 171 1318 71 31 17 4 1.77 0.48 0.30 SH w/ full N 0.78 4.85 0.15b 110 200 1482 73 15 16 3 1.74 0.53 0.29 SH w/ reduced N 0.74 4.89 0.15b 103 211 1487 76 18 16 4 2.20 0.43 0.34

Significance NS NS * NS NS NS NS NS NS NS NS NS NS Cultivar Strawberry Festival 0.73 4.68 0.16 100 178b 1396 72 25 16 3 1.88 0.45 0.29 Camino Real 0.73 4.84 0.16 118 209a 1463 74 19 16 3 1.93 0.51 0.33

Significance NS NS NS NS ** NS NS NS NS NS NS NS NS M x C interaction NS NS NS NS NS NS NS NS NS NS NS NS NS

SF: Summer Fallow; SH: Sunn Hemp; OM: Organic Matter; CEC: Cation Exchange Capacity; TN: Total Nitrogen. z Means within the same column followed by the same letter do not differ significantly by Fisher’s least significant difference test at P ≤ 0.05. y NS, *, **, *** Nonsignificant or significant at P ≤ 0.05, 0.01, or 0.001, respectively.

36

Table 2-3. Nutrient management and cultivar effects on nutrient concentrations of most recently matured leaves at early season (26 Nov. 2014, 43 DAT) and after final harvest (22 Apr. 2015, 190 DAT).

Treatment

Early season N P K Ca Mg S Fe Mn Zn Cu B

(%) (%) (%) (%) (%) (%) (ppm) (ppm) (ppm) (ppm) (ppm)

Management SF with full N 3.18 0.47 1.75 1.41 0.57 0.21 74 45 16 3.4 30.3 SH with full N 3.20 0.44 1.85 1.41 0.58 0.21 73 46 15 3.6 31.4 SH with reduced N 3.15 0.44 1.83 1.46 0.59 0.20 69 39 14 3.5 30.9

Significancey NS NS NS NS NS NS NS NS NS NS NS Cultivar Strawberry Festival 3.21 0.41bz 1.85 1.49 0.60 0.21 71 43 14b 3.3b 30.8 Camino Real 3.15 0.48a 1.77 1.37 0.56 0.20 73 44 17a 3.8a 30.9

Significance NS ** NS NS NS NS NS NS *** * NS M x C interaction NS NS NS NS NS NS NS NS NS NS NS

Late season N P K Ca Mg S Fe Mn Zn Cu B

Treatment (%) (%) (%) (%) (%) (%) (ppm) (ppm) (ppm) (ppm) (ppm)

Management SF with full N 1.94 0.32 2.22 1.18 0.39 0.20a 70 22b 20 5.3 17.6 SH with full N 2.07 0.33 2.38 1.18 0.34 0.19b 73 20b 20 5.4 18.6 SH with reduced N 2.00 0.30 2.17 1.22 0.36 0.19b 71 30a 18 5.6 17.6

Significance NS NS NS NS NS * NS ** NS NS NS Cultivar Strawberry Festival 2.02 0.33a 2.25 1.23 0.38a 0.20a 75a 25a 19 5.3 19.7a Camino Real 1.99 0.31b 2.26 1.16 0.34b 0.19b 67b 23b 19 5.5 16.4b

Significance NS * NS NS ** * * * NS NS ** M x C interaction NS ** NS NS NS * NS NS NS NS *

SF: Summer Fallow; SH: Sunn Hemp; N: Nitrogen; P: Phosphorus; K: Potassium; Ca: Calcium; Mg: Magnesium; S: Sulfur; Cu: Copper; Fe: Iron; Mn: Manganese; Zn: Zinc. z Means within the same column followed by the same letter do not differ significantly by Fisher’s least significant difference test at P ≤ 0.05. y NS, *, **, *** Nonsignificant or significant at P ≤ 0.05, 0.01, or 0.001, respectively.

37

Table 2-4. Above- and below-ground biomass and estimation of total N, P, and K accumulation by strawberry plants.

Treatment

Above-ground

biomass (g)

Below-ground

biomass (g) N

(g/plant) P

(g/plant)

K

(g/plant)

Management SF with full N 168.17 az 79.60 108.3 ab 18.1 a 125.0 a SH with full N 171.62 a 78.42 118.1 a 18.9 a 136.0 a SH with reduced N 145.78 b 73.38 96.9 b 14.5 b 105.3 b Significancey * NS ** * * Cultivar Strawberry Festival 155.36 75.83 104.1 17.0 117.0 Camino Real 168.35 78.43 111.4 17.4 127.3 Significance NS NS NS NS NS M x C interaction NS NS NS NS NS

SF: Summer Fallow; SH: Sunn Hemp. z Means within the same column followed by the same letter do not differ significantly by Fisher’s least significant difference test at P ≤ 0.05. y NS, *, **, *** Nonsignificant or significant at P ≤ 0.05, 0.01, or 0.001, respectively.

38

Table 2-5. Nutrient management and cultivar effects on leaf number, canopy size, crown diameter, and leaf chlorophyll content index of strawberry plants at early stage (14 Nov. and 4 Dec. 2014, 31 and 51 DAT), early and peak harvest (18 Dec. 2014 and 22 Jan. 2015, 65 and 100 DAT), and late season (12 Mar. and 22 Apr. 2015, 149 and 190 DAT).

Early season and peak harvest

Leaf number per plant

Canopy size (cm)

Crown diameter (mm)

Leaf chlorophyll content index (SPAD value)

Treatment 31

DAT 51

DAT 65

DAT 100 DAT

31 DAT

51 DAT

65 DAT

100 DAT

31 DAT

51 DAT

65 DAT

100 DAT

31 DAT

51 DAT

65 DAT

Management SF with full N 3.4 az 5.3 ab 6.3 11.4 a 13.9 ab 21.7 24.1 26.5 11.9 a 17.0 b 19.3 ab 27.9 45.0 a 49.4 50.8 SH with full N 3.4 a 5.5 a 6.2 11.6 a 14.9 a 21.8 24.4 27.0 11.8 a 17.9 a 20.0 a 30.9 45.1 a 49.4 50.5 SH with reduced N 3.0 b 4.7 b 5.7 9.8 b 12.9 b 19.9 23.1 25.5 10.6 b 16.3 b 18.2 b 26.0 41.4 b 47.9 50.7 Significancey * * NS * * NS NS NS * * * NS * NS NS Cultivar Strawberry Festival 3.5 a 6.0 a 7.1 a 12.7 a 14.2 21.6 24.9 a 27.1 a 11.7 17.3 19.5 31.3 a 43.0 47.8 b 50.1 Camino Real 3.1 b 4.4 b 5.0 b 9.2 b 13.6 20.7 22.8 b 25.5 b 11.1 16.8 18.9 25.2 b 44.6 50.0 a 51.2 Significance *** *** *** *** NS NS *** ** NS NS NS ** NS ** NS M x C Interaction NS NS NS NS NS NS NS NS NS NS NS NS NS NS NS

39

Table 2-5. Continued. Late season

Leaf number per plant

Canopy size (cm)

Crown diameter (mm)

Leaf chlorophyll content index (SPAD value)

Treatment 149 DAT 190 DAT 149DAT 190 DAT 149 DAT 190 DAT 190 DAT

Management SF with full N 15.6 17.9 25.9 28.5 36.3 55.1 41.1 SH with full N 16.9 16.5 26.7 28.9 42.1 62.6 40.7 SH with reduced N 14.0 16.7 25.1 29.5 37.9 58.5 41.6 Significance NS NS NS NS NS NS NS Cultivar Strawberry Festival 15.8 16.8 25.8 29.3 40.0 62.3 42.1 Camino Real 15.1 17.3 25.9 28.6 37.6 55.2 40.1 Significance NS NS NS NS NS NS NS M x C Interaction NS NS NS NS NS NS NS

SF: Summer Fallow; SH: Sunn Hemp. z Means within the same column followed by the same letter do not differ significantly by Fisher’s least significant difference test at P ≤ 0.05. y NS, *, **, *** Nonsignificant or significant at P ≤ 0.05, 0.01, or 0.001, respectively.

40

Table 2-6. Nutrient management and cultivar effects on total and marketable strawberry yields during the 2014-2015 production season in Citra, FL.

Marketable fruit number

Total fruit number

Marketable fruit yield

Marketable fruit yield

Total fruit yield

Total fruit yield

Average marketable fruit weight

Treatment (no./plant) (no./plant) (g/plant) (kg/ha) (g/plant) (kg/ha) (g/fruit)

Management SF with full N 11.0 22.9 az 203.1 8,744 357.0 a 15,371 a 19.0 SH with full N 10.6 22.8 a 194.5 8,374 353.3 a 15,212 a 18.9 SH with reduced N 10.3 20.4 b 179.5 7,728 309.9 b 13,343 b 18.3 Significancey NS ** NS NS * * NS Cultivar Strawberry Festival 13.4 a 25.4 a 216.9 a 9,339 a 351.8 15,147 16.2 b Camino Real 7.9 b 18.6 b 167.8 b 7,225 b 328.4 14,139 21.3 a Significance *** *** *** *** NS NS *** M x C interaction NS NS NS NS NS NS NS

SF: Summer Fallow; SH: Sunn Hemp. z Means within the same column followed by the same letter do not differ significantly by Fisher’s least significant difference test at P ≤ 0.05. y NS, *, **, *** Nonsignificant or significant at P ≤ 0.05, 0.01, or 0.001, respectively.

41

Table 2-7. Nutrient management and cultivar effects on monthly marketable and total yields per plant during the 2014-2015 production season in Citra, FL.

Marketable fruit

number

Total fruit number

Marketable fruit yield

Total fruit yield

(no./plant) (no./plant) (g/plant) (g/plant)

Treatment Dec Jan Feb Mar- Apr

Dec Jan Feb

Mar- Apr

Dec Jan Feb

Mar- Apr

Dec Jan Feb

Mar- Apr

Management SF with full N 0.9az 2.6 3.2 4.4 0.9a 4.4 5.2 12.3a 13.5a 48.1 67.1 74.3 14.1a 74.9a 100.7a 167.4 SH with full N 0.7b 2.3 3.2 4.4 0.7b 4.1 5.2 12.8b 9.9b 42.1 65.5 77.0 10.5b 64.7b 99.6b 178.4 SH with reduced N 0.6b 2.5 2.9 4.3 0.6b 4.4 4.7 10.7b 8.1b 41.4 57.1 72.8 8.8b 65.6b 87.3b 148.1 Significancey * NS NS NS ** NS NS * * NS NS NS * * * NS Cultivar

Strawberry Festival 1.1a 3.0a 4.5a 4.7 1.2a 4.9a 6.8a 12.6a 15.1a 47.7a 83.2a 70.7 16.2a 68.9 115.9a 150.7b Camino Real 0.3b 1.9b 1.7b 4.0 0.3b 3.7b 3.4b 11.2b 5.9b 40.0b 43.2b 78.7 6.2b 67.9 75.8b 178.5a Significance *** *** *** NS *** *** *** * *** * *** NS *** NS *** * M x C interaction NS NS NS NS NS NS NS NS NS NS NS NS NS NS NS NS

SF: Summer Fallow; SH: Sunn Hemp. z Means within the same column followed by the same letter do not differ significantly by Fisher’s least significant difference test at P ≤ 0.05. y NS, *, **, *** Nonsignificant or significant at P ≤ 0.05, 0.01, or 0.001, respectively.

42

Figure 2-1. Daily average soil temperature at the soil depth of 10 cm and daily average

precipitation between sunn hemp incorporation and 4 weeks after strawberry transplanting. Data source: Florida Automated Weather Network (http://fawn.ifas.ufl.edu).

0

1

2

3

4

5

6

7

8

0

5

10

15

20

25

30

Rain

fall

(cm

)

So

il te

mp

era

ture

(˚C

)Daily average rainfall

Daily average soil temperature

43

Figure 2-2. Cull fruit percentage (cull fruit weight per plant divided by total fruit weight per plant) during the during the 2014-2015 strawberry production season in Citra, FL. SF: Summer Fallow; SH: Sunn Hemp. Bars followed by the same letter do not differ significantly by Fisher’s least significant difference test at P

≤ 0.05.

30%

35%

40%

45%

50%

55%

60%

SF w/ full N SH w/ full N SH w/reduced N

SF w/ full N SH w/ full N SH w/reduced N

Cull

pe

rcen

tage

Strawberry Festival

ab

a

b

Camino Real

b

a a

44

Figure 2-3. Classifications of fruit and percentage distribution based on cull fruit weight during the 2014-2015 strawberry production season in Citra, FL. SF: Summer Fallow; SH: Sunn Hemp.

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

SF w/full N SH w/full N SHw/reduced N

SF w/full N SH w/full N SHw/reduced N

Cull

pe

rcen

tage

Strawberry Festival

Botrytis Insect Damage Anthracnose Deformed

Soft Rot Rodent Leather Rot Rain Damage

Small Other

Camino Real

45

CHAPTER 3 IMPACTS OF NUTRIENT MANAGEMENT INVOLVING SUNN HEMP ON ORGANIC

STRAWBERRY FRUIT QUALITY

Introduction

Strawberry has gained popularity among consumers due to its sweet, juicy taste

and high nutritional value. Rich in vitamin C and other phytochemicals such us

polyphenols, strawberry has been suggested to promote human wellness by reducing

the risk of cancer and cardiovascular diseases (Battino et al., 2009; Giampieri et al.,

2012; Giampieri et al., 2013). As an important small fruit in Florida, strawberry was

planted on over 4,450 hectares in 2015 with a production value of $290 million (USDA

National Agricultural Statistics Service, 2016). With the increase in organic food

consumption, consumer willingness to purchase organic strawberry is rising despite the

premium price (Oberholtzer et al., 2005), Growers’ interest in producing organic

strawberry is also growing according to the recent U.S. organic production surveys

(USDA, 2010; USDA, 2016).

Many studies have shown that different cultural practices and nutrient

management strategies can markedly influence fruit quality. For example, anthocyanin

and acidity content of black chokeberry (Aronia melanocarpa Ell.) reduced when

fertilization level increased (Jeppsson, 2000); lower firmness and titratable acidity (TA)

content of apple (Malus domestica L.) were found when higher N rates applied (Raese

et al., 2007). However, mixed results regarding total soluble solids (TSS) were reported

as studies showed that TSS content of black chokeberry and strawberry was not

affected by N fertilization rate (Jeppsson, 2000; Miner et al., 1997), while others

indicated that strawberry fruit soluble solids level decreased as N level increased

(Cantliffe et al.,2007; Mukkun et al. 2000). With respect to the effects of organic cultural

46

practices on strawberry fruit quality, Wang and Lin (2002) found that organic acids,

sugars, TSS, and TA content were increased by adding compost to soil mix. Singh et al.

(2008) demonstrated that strawberry fruit were firmer, had higher TSS and VC but lower

acidity when vermicompost was used in combination with inorganic fertilizer. On the

contrary, Hargreaves et al. (2008) pointed out that organic amendments did not improve

strawberry fruit antioxidant capacity compared with inorganic fertilizers. Similarly,

Häkkinen and Torronen (2000) reported that organic cultivation had no consistent effect

on strawberry fruit total phenolic content (TPC). Strawberry fruit TSS, TA, VC, flavonoid,

and total sugar contents as well as antioxidant capacity were found to be elevated in hill

plasticulture more so than a matted row growing system (Wang et al., 2002). Moreover,

weather conditions, especially precipitation can cause variations in strawberry quality

traits from year to year (Tulipani et al., 2011).

Genotype, pre-harvest practice, and postharvest handling are major factors that

influence strawberry fruit composition and sensory quality as well as postharvest shelf

life (Kader, 2008). Pre-harvest practices, such as nutrient management, may result in

differences in postharvest shelf-life of horticultural crops. Excess N may lead to

increased susceptibility to postharvest decay, while Ca deficiency may be related to a

range of physiological disorders (Hewett, 2006). Instrumental analyses of compounds

contributing to flavor are usually used to study fruit quality. However, sensory flavor,

serving as another quality perspective, are given less attention. Sensory testing

provides another fruit quality perspective in terms of interpretation of sensory

experiences perceived by humans. In addition to instrumental analyses, sensory

evaluation involves a different approach for better understanding of different quality

47

traits and their influence on perceived sensory attributes by humans. Guan et al. (2015)

indicated that sensory evaluation of specialty melons combined with instrumental

analyses helped better interpret fruit quality characteristics.

Cover crop rotation is an important component of nutrient management program

for organic crop production and has been adopted by many growers in Florida. Proper

use of cover crops may greatly improve soil quality by stimulating soil microbial activity,

elevating soil organic matter, and reducing soil erosion. Additionally, weed suppression

by cover crops has been proven by numerous studies (Brennan and Smith., 2005;

Dhima et al., 2006; Stivers-Young, 1998; Teasdale, 1996). Contributions of leguminous

cover crops to soil available nitrogen (N) are also increasingly recognized (Ebelhar et

al., 1984; Muramoto et al., 2011; Parr et al., 2014). The amount of N provided by cover

crops varies among different cover crops as a result of differences in biomass

production and N content in plant tissues (Newman et al., 2010; Ozores-Hampton,

2012). The N release rate from cover crop residue is another factor determining the

amount of available N provided by cover crops (Ranells and Wagger, 1996), which

largely depends on environmental conditions and the C:N ratio of the cover crop at

termination (Quemada and Cabrera, 1997; USDA Natural Resources Conservation

Service, 2011).

Summer cover crops have been used as a weed control method in fall and winter

organic strawberry production in Florida. Sunn hemp as one of the common summer

legumes used in Florida can produce 5,000–11,200 kg/ha dry biomass and contribute

100–200 kg/ha total N to the following crop (Li et al., 2009; Newman et al., 2010;

Schomberg et al., 2007). Although sunn hemp has been increasingly used as a summer

48

rotational crop with organic strawberry production by growers, research-based

information is rather limited with regard to the effects of integration of sunn hemp

residue into organic strawberry production on fruit quality attributes of the following

strawberry crop.

In this study, nutrient management practices with sunn hemp as a summer cover

crop and their interactions with strawberry cultivars in organic production systems were

assessed in terms of their influence on strawberry fruit composition, postharvest quality,

and sensory attributes.

Materials and Methods

Experimental Design and Field Trial Establishment

The field experiment was conducted in the 2014–2015 strawberry season and

was arranged in a split-plot design with 4 replications. Sunn hemp was seeded on 17

July 2014 at a rate of 44.8 kg/ha and then mowed and tilled on 22 Sept. 2014 (67 days

of establishment). A total of six treatments consisting of three nutrient management

practices: 1) sunn hemp with preplant N fertilizer at full rate (84 kg/ha), 2) sunn hemp

with preplant N fertilizer at reduced rate (19.8 kg/ha), and 3) summer fallow without

sunn hemp and with preplant N fertilizer at full rate (84 kg/ha) as the whole plot factor,

and two short-day strawberry cultivars: Strawberry Festival and Camino Real as the

subplot factor were evaluated in this study. Strawberry plug plants (Luc Lareault

Nursery, Quebec, Canada) were transplanted into double rows spaced 30.5 cm apart

on raised beds spaced 152.4 cm apart on centers on 14 Oct. 2014. Preplant fertilization

was applied using a mixture of MicroSTART60 3N-0.9P-2.5K (Perdue AgriRecycle,

LLC., Seaford, DE), Howard Organic Bonemeal 7N-5.2P-0K (Howard Fertilizer &

Chemical Co., Inc., Orlando, FL), and Jobe’s Organics Bone Meal 2N-6.1P-0K (Easy

49

Gardener Products, Inc., Waco, TX); in-season fertigation was applied using Howard

Organic [GATOR 96002 Organic Liquid 3N-0P-5.0K; Howard Fertilizer & Chemical Co.,

Inc., Orlando, FL]. Therefore, whole season fertilization consisted of 236.2, 45.5, and

275 kg/ha of N, P and K, respectively, for full rate, and 172, 38.8, and 259.2 kg/ha of N,

P and K, respectively, for reduced rate.

Strawberries with ≥ 80% red color were harvested from 4 Dec. 2014 [51 days

after transplanting (DAT)] to 6 Apr. 2015 (174 DAT), with 26 harvests in total. Fruit

samples were selected from marketable berries with uniform size and color, and were

stored at 1˚C and 95% relative humidity for postharvest quality evaluation and sensory

analysis or at -20˚C for fruit composition analyses.

Detailed information regarding field trial establishment and strawberry harvest

can be found in Chapter 2.

Fruit Composition Analyses

Fruit composition including TSS, TA, total monomeric anthocyanins (TMA), TPC,

and VC was analyzed in strawberries from four harvests made throughout the season: 3

Jan. (81 DAT), 2 Feb. (111 DAT), 16 Mar. (153 DAT), and 30 Mar. 2015 (167 DAT),

respectively. After each harvest, fruit samples were transported in coolers from Citra to

the Gainesville campus and then frozen at -20˚C within 24 hours until fruit quality

assessment. At analysis, around 8 frozen berries were thawed at room temperature and

homogenized in a 908™ Commercial Bar Blender (HBB908) (Hamilton Beach Brands,

Inc., Southern Pines, NC). A strawberry puree sample of around 20 g was centrifuged

for 20 min at 12,000 rpm and 4˚C and filtered using four layers of cheesecloth to obtain

a clarified extract for TSS and TA analyses. For TMA and TPC analyses, a 1 g sample

of the strawberry puree was extracted with 10 ml methanol/water/acetic acid (85:15:0.5;

50

v/v/v), centrifuged for 20 min at 12,000 rpm and 4˚C, and supernatant filtered through

four-layer cheesecloth to obtain a clarified extract. For VC analysis, 1 g of strawberry

puree was extracted with 10 ml acid mixture (6% HPO3 containing 2N acetic acid),

centrifuged for 20 min at 15,000 rpm and 4˚C and the supernatant filtered through four-

layer cheesecloth to obtain a clarified extract.

The TSS of strawberry juice was measured with an automatic temperature-

compensated digital refractometer Digital Brix/RI-Chek (Reichert Inc., Depew, NY) and

expressed as % soluble solids. Initial pH and TA of strawberry juice were measured

using a Metrohm® Sample Processors automatic titrimeter (Metrohm USA, Inc.,

Riverview, FL); 6 ml of strawberry extract was titrated to an endpoint of pH = 8.2 with

0.1 N sodium hydroxide and TA was expressed as % citric acid. TMA was assessed

using a pH differential spectroscopic method described by Tonutare et al., 2014.

Absorbance was recorded at 520 nm and 700 nm by a SpectraMax 190 microplate

spectrophotometer (Molecular Devices, Sunnyvale, CA) and results were expressed on

a fresh weight basis (mg/100 g FW). TPC was determined by the Folin-Ciocalteu

method (Slinkard ad Singleton, 1977). Absorbance was measured using the

SpectraMax 190 at 765 nm. A standard curve was generated by using gallic acid to

determine the concentration of total phenolics, and results were expressed as gallic acid

equivalent (mg GAE/g FW). VC was analyzed by a dinitrophenylhydrazine (DNPH)

method described by Terada et al. (1978). L-ascorbic acid analytical standard was used

to produce a standard curve. Absorbance was read at 540 nm with a PowerWave HT

Microplate Spectrophotometer (Biotek ®, Winooski, VT) and results were expressed as

mg/100 g FW.

51

Quality Evaluation During Shelf Life

A quality evaluation study during 9 days of storage was carried out to evaluate

strawberry fruit quality decline over time by following commercial storage practice.

Eighteen strawberries per plot from the 23 Mar. 2015 harvest were stored at 1˚C and

95% relative humidity in 473.2 ml (1 pint) clamshells, marked as day 0. Three

strawberries in one clamshell were monitored for fruit mass loss and visual quality every

2 days from day 1 until day 9 of storage. Three strawberries were used at each

assessment time for color and firmness measurements every 2 days from day 1 until

day 9 of storage. A 1-5 subjective rating scale (Nunes, 2015) was used to evaluate fruit

visual quality: 5.0 = excellent, 4.5 = very good, 4.0 = good, 3.5 = good to acceptable,

3.0 = acceptable, 2.5 = acceptable to poor, 2.0 = poor/non-salable under normal

conditions, 1.5 = poor to very poor/not salable, 1.0 = very poor. Strawberry external

color was measured using a chroma meter (Model CR-400, Konica Minolta Sensing

Americas, Inc., NJ) and expressed as C.I.E. lightness, chroma, and hue (L*c*h*). Two

readings from the opposite sides of each fruit were recorded for the color measurement.

Fruit firmness was measured using a hand-held penetrometer (Fruit TestTM FT, Wagner

Instruments, Greenwich, CT) with an 8 mm Magness-Taylor-type probe and expressed

as kg-force.

Consumer Sensory Analysis

Consumer sensory analysis was only conducted on ‘Strawberry Festival’ fruit.

Strawberries were harvested on 29 Jan. 2015 and assessed on 30 Jan. 2015 at the

University of Florida Sensory Analysis Laboratory in Gainesville, FL. after over-night

storage at 1˚C. Strawberries were washed and cut to remove calyx, served to 112

consumer panelists as one whole berry for each treatment. All 6 orders in which the

52

strawberry samples were given to each panelist were presented an equal number of

times. The sensory tests began with three demographic questions: gender, age, and

frequency of fresh strawberry consumption (Table 3-2). Each panelist was then asked to

score each of the attributes using a hedonic scale or a just-about-right scale and directly

enter the ratings into the computer following the instructions provided. Overall

appearance, overall acceptability, texture, strawberry flavor, and sweetness were

assessed using a 1-9 hedonic scale: 1 = dislike extremely, 2 = dislike very much, 3 =

dislike moderately, 4 = dislike slightly, 5 = neither like nor dislike, 6 = like slightly, 7 =

like moderately, 8 = like very much, 9 = like extremely. A 1-5 just-about-right scale was

employed to assess strawberry firmness: 1 = much too soft, 2 = somewhat too soft, 3 =

just about right, 4 = somewhat too firm, 5 = much too firm. Panelists were asked to

clean their palates between samples using saltine crackers and water. After completing

the taste test, each panelist was compensated for their participation. All procedures

used were approved by the University of Florida Institutional Review Board.

Statistical Analysis

Data analysis was performed using Glimmix procedure of SAS statistical

software (Version 9.2; SAS Institute, Cary, N.C.) following the split plot design used.

Multiple comparisons of different measurements among treatments were conducted by

Fisher’s Least Significant Difference (LSD) test at α = 0.05.

Results and Discussion

Fruit Chemical Composition

Overall, strawberry cultivar had greater effects than nutrient management

practices on fruit composition measurements. No significant differences were found in

TA, pH, TPC, or VC of strawberry fruit between the sunn hemp treatments and the

53

summer fallow control at any sampling date throughout the season, whereas significant

differences were observed in TSS at 167 DAT (30 Mar. 2015) and TMA at 153 DAT (16

Mar. 2015), respectively (Table 3-1). In the case of TSS, fruit from the summer fallow

control showed higher value than that of the sunn hemp treatments, while similar values

were found in the full preplant fertilization and reduced preplant fertilization sunn hemp

treatments (Table 3-1). TMA was higher in the summer fallow control than in the full

fertilization sunn hemp treatment but did not differ significantly from the reduced

fertilization sunn hemp treatment, similar levels of TMA were observed in the two sunn

hemp treatments as well (Table 3-1). Strawberry cultivars, on the other hand,

demonstrated some pronounced effects on fruit TSS and TA, whereas fewer cultivar

effects were shown on VC, pH, TMA, and TPC (Table 3-1). ‘Strawberry Festival’ fruit

had higher TSS than ‘Camino Real’ from 81 to 153 DAT (3 Jan.–16 Mar. 2015),

together with higher TA content from 111 to 153 DAT (2 Feb.–16 Mar. 2015), as well as

higher pH level at 81 DAT (3 Jan. 2015) and TPC concentration at 153 DAT (16 Mar.

2015), while ‘Camino Real’ produced more TMA at 81 DAT (3 Jan. 2015) (Table 3-1).

No nutriment management by cultivar interaction was detected among all fruit

composition parameters in all the samplings (Table 3-1). While comparing across

sampling days, TSS, TA, and TMA content of both cultivars, regardless of nutrient

management practices, were the highest (9.8 % soluble solids, 0.86 % citric acid, and

20.7 mg/100 g FW, respectively) at 111 DAT (2 Feb. 2015) and decreased afterwards

(Table 3-1). The VC and TPC were maintained at similar levels from 81 to 153 DAT (3

Jan.–16 Mar. 2015) while fruit VC level tended to decrease but TPC level tended to

increase towards the end of the strawberry season (Table 3-1). In the meantime, pH

54

value followed an elevating trend from a mean value of 3.58 at 81 DAT (3 Jan. 2015) to

3.83 at 167 DAT (30 Mar. 2015) (Table 3-1).

The levels of fruit TSS and TA ranged from 5.8 to 10.1% and 0.51 to 0.91%,

respectively, in all samplings, which were comparable to those of strawberries

measured by others (Hargreaves et al., 2008; Mishra and Kar, 2014; Wang et al., 2002).

Strawberry fruit showed an average VC of 41.5 mg/100 g FW in four samplings, which

was similar as the value reported by Mishra and Kar (2014) but a little higher than

results reported by Koyuncu and Dilmaçünal, 2010). Strawberry TMA level was around

17.8 mg/100 g FW for the season, which was consistent with the range of 18.5–24.2

mg/100 g FW indicated by Zheng et al. (2005). The mean fruit TPC for the season was

1.72 mg GAE/g FW, which was in accordance with mean TPC levels of 1.09 and 2.29

mg GAE/g FW documented by Moreno et al. (2010) and Gündüz and Özdemir (2014),

respectively.

In the present study, no significant differences were observed in TA, pH, TMA,

TPC, and VC levels between full and reduced preplant fertilization rates, which agrees

with the results of research with strawberry, black chokeberry, and pepper regarding

fertilization rate reported by others (Häkkinen and Torronen, 2000; Jeppsson, 2000;

Miner et al., 1997; Pascual et al., 2010). However, decreased TSS, TA, and VC levels,

as well as firmness of strawberry, and apple with increased N fertilization rates were

reported in previous studies (Cantliffe et al., 2007; Lee and Kader, 2000; Raese et

al.,2007). The TSS content was similar among nutrient management practices from 81

to 153 DAT (3 Jan.–16 Mar. 2015), however, it was found to be lower in sunn hemp

treatments regardless of preplant fertilization level at 167 DAT (30 Mar. 2015). The

55

findings from previous studies of nutrient management effects on strawberry quality are

inconclusive. Strawberry fruit TSS, TA, organic acids, and sugars were found to be

promoted by supplemental compost (Wang and Lin, 2002), while higher strawberry fruit

TSS and VC, and lower TA contents were observed when the soil was amended with

vermicompost (Singh et al. 2008). In contrast, studies on strawberry revealed that

organic amendments did not improve fruit antioxidant capacity compared with inorganic

fertilization (Hargreaves et al., 2008). Neuweiler et al. (2003) indicated that TA of

strawberry fruit was higher in a straw and white clover (Trifolium repens L.) living mulch

system than the bare ground control, while the firmest fruit were observed in the bare

ground control when 60 kg/ha N fertilizer was applied. The similarity of strawberry fruit

TSS, TA, pH, TMA, TPC and VC contents among different nutrient management

practices demonstrates the potential to reduce fertilization rate along with sunn hemp

incorporation in organic strawberry production systems for maintaining fruit quality.

In general, cultivar effects outweighed nutrient management effects in terms of

fruit composition, which concurs with the conclusion of Capocasa et al. (2008) that

strawberry genotype effects on strawberry nutritional quality were greater than that of

the cultivation conditions. Previous studies have shown that compositional variations of

fruits can be genotype specific. June-bearing strawberry cultivars exhibited higher TPC

and antioxidant capacity than day-neutral genotypes (Khanizadeh et al., 2006; Tsao et

al., 2007). Whitaker et al. (2011) observed a wide range of genotype differences in

strawberry TSS to TA ratio. Furthermore, Warner et al. (2004) reported that tomato fruit

TSS, firmness, and color were not affected by N fertilization rates, which however were

strongly influenced by cultivars. Fruit VC and TMA contents were reported to differ

56

among strawberry cultivars as well (Crespo et al., 2010; Olsson et al., 2004; Tulipani et

al., 2008).

Quality Assessment During Shelf Life and Consumer Sensory Evaluation

Strawberry fruit surface color did not differ among nutrient management practices

during the 9 days of storage. However, cultivar effects were significant over time

regarding L and H but not C (Table 3-3). ‘Strawberry Festival’ had higher L and H

values than ‘Camino Real’ consistently throughout storage in this study, which indicates

lighter and less red color on ‘Strawberry Festival’ fruit surface. No nutrient management

by cultivar interaction was detected in terms of strawberry external color during storage

(Table 3-3). Significant differences in fruit mass loss were observed between strawberry

cultivars over time during the postharvest storage at 1˚C and 95% relative humidity

(Figure 3-1). ‘Camino Real’ showed lower percentage of mass loss compared with

‘Strawberry Festival’ from storage Day 3 to Day 9 with initial mass at Day 1 as the

baseline, while ‘Strawberry Festival’ fruit were lighter in color than ‘Camino Real’ with an

overall declining slope of lightness (Figure 3-1). Significant cultivar differences were

observed in subjective ratings of fruit quality during storage on Day 1 and nutrient

management by cultivar interaction was found at Day 3, such ‘Camino Real’ in the sunn

hemp residue with full preplant fertilization treatment had significant lower visual quality

than in the other two treatments, but did not differ from ‘Strawberry Festival’ (Data not

shown). Higher visual quality of ‘Camino Real’ was recorded on Day 1 but the subjective

ratings did not differ between cultivars for the remainder of storage (Figure 3-2).

‘Strawberry Festival’ fruit were firmer than Camino Real’ at Day 1 and Day 9 (Figure 3-

2). Nutrient management by cultivar interaction was also found on Day 1, ‘Strawberry

Festival’ fruit were firmer than ‘Camino Real’ in the summer fallow control and both

57

‘Strawberry Festival’ and ‘Camino Real’ in the sunn hemp treatments were firmer than in

the summer fallow treatment (Data not shown). The results indicated that the major

differences in strawberry postharvest quality over time were among strawberry cultivars

but not nutrient management practices. ‘Strawberry Festival’ tended to lose fruit mass

faster but maintained lighter red external color than ‘Camino Real’ during storage at 1˚C

and 95% relative humidity.

Overall acceptability by consumers did not differ among ‘Strawberry Festival’ fruit

harvested from full or reduced preplant fertilization plots with sunn hemp and summer

fallow plots (Table 3-4). Additionally, consumers did not perceive any pronounced

differences in terms of strawberry flavor, sweetness, texture, or firmness between

‘Strawberry Festival’ fruit harvested from sunn hemp treatments with full or reduced

preplant N fertilization rates and the summer fallow control (Table 3-4 and 3-5). These

results from the consumer sensory evaluation were consistent with the results from the

instrumental measurements (Table 3-1), which concurred with Schwieterman et al.

(2014) who suggested that hedonic ratings of strawberry fruit are highly related to

specific compounds.

Conclusions

The findings from the present study demonstrate that cultivar effects outweigh

the influence of the tested nutrient management practices with respect to strawberry

fruit quality attributes and postharvest quality during shelf life. While more research

efforts are directed towards optimizing nutrient management for organic strawberry

production including the use of cover crops and other organic amendments to improve

crop growth and yield performance, it would also be important to assess different

58

cultivars in terms of any fruit quality modifications as affected by these nutrient

management systems.

59

Table 3-1. Nutrient management and cultivar effects on total soluble solids (TSS), titratable acidity (TA), pH, total monomeric anthocyanins (TMA), total phenolic content (TPC), and vitamin C (VC) of strawberry fruit from four harvests: 3 Jan. (81 DAT), 2 Feb. (111 DAT), 16 Mar. (153 DAT), and 30 Mar. 2015 (167 DAT) in the field trial at Citra, FL.

Quality attributes DAT

Management Cultivar

M x C interactiony

SF with full N

SH with full N

SH with reduced N

Strawberry Festival

Camino Real

TSS (% soluble solids)

81 8.4 7.9 7.9 8.5 a 7.7 b NS 111 10.1 9.6 9.7 10.1 a 9.5 b NS 153 6.6 6.1 6.3 6.8 a 5.8 b NS 167 7.2 az 6.4 b 6.2 b 6.8 6.4 NS

TA (% citric acid)

81 0.72 0.74 0.74 0.74 0.74 NS 111 0.86 0.84 0.87 0.91 a 0.80 b NS 153 0.67 0.76 0.67 0.74 a 0.66 b NS 167 0.55 0.52 0.54 0.56 0.51 NS

pH

81 3.62 3.56 3.56 3.62 a 3.53 b NS 111 3.58 3.61 3.56 3.58 3.59 NS 153 3.67 3.59 3.69 3.66 3.64 NS 167 3.86 3.80 3.82 3.81 3.85 NS

TMA (mg/100 g FW)

81 15.7 15.4 16.3 13.8 b 17.9 a NS 111 20.9 19.9 21.3 19.7 21.7 NS 153 20.6 a 16.9 b 19.3 ab 19.5 18.3 NS 167 16.5 15.2 15.1 15.8 15.4 NS

TPC (mg GAE/g FW)

81 1.47 1.54 1.49 1.53 1.47 NS 111 1.59 1.82 1.72 1.78 1.64 NS 153 1.73 1.80 1.59 1.80 a 1.61 b NS 167 1.85 2.04 1.97 1.89 2.02 NS

VC (mg/100 g FW)

81 43.4 46.4 41.5 44.9 42.6 NS 111 46.0 45.3 45.2 48.5 42.5 NS 153 46.8 40.5 43.8 43.6 43.8 NS 167 36.3 32.9 30.1 34.7 31.6 NS

DAT: Days After Transplanting; SH: Sunn Hemp; SF: Summer Fallow. z Means within the same row followed by the same letter do not differ significantly by Fisher’s least significant difference test at p ≤ 0.05. y NS, *, **, *** Nonsignificant or significant at P ≤ 0.05, 0.01, or 0.001, respectively.

60

Table 3-2. Demographic information about consumers participating in sensory analysis of ‘Strawberry Festival’ fruit.

Characteristic Category Consumersz (%)

Gender Male 38.4

Female 61.6

Age (years)

Under 18 1.8 18-29 66.1 30-44 11.6 45-65 17.9

Over 65 0.9

Fresh strawberry consumption frequency

Once a day 1.8 2-3 times a week 19.6

Once a week 24.1 2-3 times a month 31.3

Once a month 15.2 Twice a year 8.0 Once a year 0.0

Never 0.0 z 112 consumers participated on 30 Jan. 2015.

61

Table 3-3. Changes in strawberry fruit color during storage at 1˚C and 95% relative humidity.

Color DOS

Management Cultivar

M x C interactiony

SF with full N

SH with full N

SH with reduced N

Strawberry Festival

Camino Real

L*

1 25.72 25.99 25.74 26.95 az 24.68 b NS 3 25.56 25.68 26.05 26.47 a 25.05 b NS 5 26.52 27.26 27.18 27.17 26.80 NS 7 25.15 24.70 25.77 26.44 a 23.98 b NS 9 25.83 25.54 25.18 26.29 a 24.74 b NS

C*

1 31.94 33.35 32.24 33.22 31.80 NS 3 31.47 32.22 32.40 32.12 31.94 NS 5 28.52 28.96 31.13 28.10 30.97 NS 7 27.86 28.47 30.45 29.69 28.16 NS 9 31.50 30.38 30.13 30.56 30.78 NS

H*

1 29.98 31.08 30.06 32.01 a 28.73 b NS 3 29.65 29.56 29.03 31.14 a 27.68 b NS 5 27.53 28.09 28.95 28.74 27.64 NS 7 29.58 28.05 29.43 31.03 a 27.00 b NS 9 29.65 28.24 30.91 29.48 29.72 NS

DOS: Days of Storage; SH: Sunn Hemp; SF: Summer Fallow. z Means within the same row followed by the same letter do not differ significantly by Fisher’s least significant difference test at p ≤ 0.05. y NS, *, **, *** Nonsignificant or significant at P ≤ 0.05, 0.01, or 0.001, respectively.

62

Table 3-4. Consumer sensory ratingsz of strawberry fruit quality attributes for ‘Strawberry Festival’ grown under different nutrient management practices.

Management Overall

acceptability Strawberry

Flavor Texture Sweetness

SF with full N 6.43 6.69 6.56 6.22 SH with full N 6.35 6.40 6.44 5.97 SH with reduced N 6.66 6.45 6.41 6.00 Significancey NS NS NS NS

SF: Summer Fallow; SH: Sunn Hemp. z Overall acceptability, strawberry flavor and sweetness were scored using a nine-point hedonic scale (1 = dislike extremely, 2 = dislike very much, 3 = dislike moderately, 4 = dislike slightly, 5 = neither like nor dislike, 6 = like slightly, 7 = like moderately, 8 = like very much, 9 = like extremely); 112 consumers participated on 30 Jan. 2015. y NS, *, **, *** Nonsignificant or significant at P ≤ 0.05, 0.01, or 0.001, respectively.

63

Table 3-5. Percentage distribution of panelists in sensory evaluation of strawberry fruit firmness levelz for ‘Strawberry Festival’ grown under different nutrient management practices on 30 Jan. 2015.

Firmness level (%) Management 1 2 3 4 5

SF with full N 0.0 3.6 61.6 27.1 7.1 SH with full N 0.9 2.7 57.1 27.7 11.6 SH with reduced N 0.0 7.1 51.8 35.7 5.4

SF: Summer Fallow; SH: Sunn Hemp. z Firmness level was evaluated with a Just-About-Right scale (1 = much too soft, 2 = somewhat too soft, 3 = just about right, 4 = somewhat too firm, 5 = much too firm); 112 consumers participated on 30 Jan. 2015.

64

Figure 3-1. Strawberry fruit fresh mass loss and external lightness change over time

during storage at 1˚C and 95% relative humidity. SF: ‘Strawberry Festival’; CR: ‘Camino Real’. Dots followed by the same upper or lower case letter on the same sampling date do not differ significantly by Fisher’s least significant

difference test at P ≤ 0.05. Upper case letters denote comparisons in

lightness between cultivars, lower case letters denote comparisons in mass loss between cultivars. Mass loss percentage was calculated with sample mass at Day 1 as baseline.

23

23.5

24

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%)

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65

Figure 3-2. Visual fruit quality ratings of strawberries and fruit firmness of ‘Strawberry

Festival’ and ‘Camino Real’ during storage at 1˚C and 95% relative humidity. SF: ‘Strawberry Festival’; CR: ‘Camino Real’. A 1-5 visual fruit quality and decay rating scale was used: 5.0 = excellent, 4.5 = very good, 4.0 = good, 3.5 = good to acceptable, 3.0 = acceptable, 2.5 = acceptable to poor, 2.0 = poor/non-salable under normal conditions, 1.5 = poor to very poor/not salable, 1.0 = very poor. Dots followed by the same upper or lower case letter on the same sampling date do not differ significantly by Fisher’s least significant

difference test at P ≤ 0.05. Upper case letters denote comparisons in

subjective rating of fruit quality between cultivars, lower case letters denote comparisons in fruit firmness between cultivars.

1

1.5

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kg-f

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CR Quality Rating

a

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CHAPTER 4 INFLUENCE OF FERTILIZERS FROM DIFFERENT NITROGEN SOURCES ON

STRAWBERRY GROWTH, YIELD AND QUALITY

Introduction

Organic fertilizers are an important nutrient source for organic crop production at

present, and different forms of organic fertilizers of various nutrient compositions have

been used by organic growers. In addition to preplant application in solid fertilizer forms,

organic fertilizers with greater solubility are used for in-season fertigation during crop

production to meet nutrient demand at different plant growth and development stages.

Common organic fertilizers and amendments are derived from plant- or animal-based

materials and natural mineral substances (Gaskell and Smith, 2007; Guertal and Green,

2012; Mikkelsen and Hartz, 2008). Among various types of organic fertilizers, fish-based

fertilizers have been studied as a N source in horticultural crops such as blackberry

(Rubus L.), tomato and long bean (Vigna unguiculata L.) (Aranganathan and Rajasree,

2016; Fernandez-Salvador and Strik, 2015; Staley et al., 2013), whereas humate

fertilizer or humic acid was brought to the attention of organic growers, as the substance

was proven to be growth stimulator for most horticultural crops (Adani et al., 1998;

Haghighi et al., 2013; Orlova and Arkhipchenko, 2009). Particularly rich in potassium (K)

and micronutrients as well as growth stimulators (Blunden, 1991; Papenfus et al., 2013;

Reitz and Trumble, 1996), seaweed and seaweed-derived products have been explored

in okra (Abelmoschus esculentus L.), tomato, and lettuce (Lactuca sativa L.) (Divya et

al., 2015; Illera-Vives et al., 2015; Zodape et al., 2008).

Fertilizers from different nutrient sources may vary in nutrient form, composition,

and availability, thus showing different impact on plant growth, fruit yield and quality.

Compost derived from seaweed and fish waste at 66 t/ha resulted in higher tomato

67

yield, as well as increased yield of subsequent lettuce (Illera-Vives et al., 2015). In

addition, liquid seaweed fertilizer was indicated to promote growth, yield, and quality of

okra as shown by increased leaf and flower numbers, fresh and dry weight of plant, as

well as fruit yield and mineral contents (Divya et al., 2015; Zodape et al., 2008). Khan et

al. (2009) indicated that seaweed extracts benefit crop growth and yield as a result of

alleviating environmental stresses and promoting soil health as shown by enhancing soil

moisture-holding capacity and beneficial soil microbial activity. Fish-based organic

fertilizer was discovered to promote growth of tomato plants by enriching soil organic C

compared with chemical fertilizer (Aranganathan and Rajasree, 2016). However, plant

growth, yield, and fruit quality of blackberry did not differ between two organic fertilizer

treatments: corn steep liquor with fish waste and fish/molasses blend, and sufficient

nutrients were provided from both fertilizers (Fernandez-Salvador and Strik, 2015).

Arancon et al. (2004a) found that strawberry growth and yield were improved

significantly by vermicompost application, which might be related to the enhanced

earthworm and microbial activity and the increased level of humic substances in the

soil. Atiyeh et al. (2002) illustrated that humic acids from vermicomposts had promoting

effects on growth of tomato and cucumber (Cucumis sativus L.) plants concerning plant

height, leaf area, and plant dry weight.

In addition to organic fertilizers from plant- and animal-related sources, natural

deposit products, particularly mineral deposits, have been employed to provide N, P,

and K for growing organic crops. Major mineral products that have been approved for

organic use include rock phosphate, potassium chloride, and kainite [Organic Materials

Review Institute (OMRI), 2016]. Sulfate of potash (SOP) containing 50% K2O and 18%

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S is natural mineral which provides reliable K to meet plant need for fruit quality

development, and can also be used in organic production. Ali and Rab (2016) found that

supplemental K from SOP resulted in better growth of tomato in terms of fresh and dry

root and shoot weights as well as leaf counts than K from muriate of potash (MOP) and

no potash control. Sodium nitrate is a naturally occurring mined product from surface

deposits. It is an effective nutrient source because all of the N present in the substance

is readily available for crop uptake, and as a matter of fact, it resembles the behavior of

conventional chemical fertilizer in the form of NaNO3. The mineralization of carbon-

based organic N sources is not always rapid enough to meet the N demand of the

growing crop, while sodium nitrate has been preferred by some organic growers as a

fast release fertilizer to cope with such a situation. Prior to 21 Oct. 2012, sodium nitrate

was identified by the National Organic Program (NOP) as a prohibited nonsynthetic

substance that may not be used in organic production unless its use is restricted to no

more than 20% of the crop’s total nitrogen requirement (7 CFR 205.602). With the

expiration of this rule due to the sunset provision in the Organic Foods Production Act of

1990, sodium nitrate is not currently listed as a prohibited substance by NOP and the

20% restriction has been removed. However, the usage of sodium nitrate under organic

production is subject to all requirements of the soil fertility and crop nutrient

management practice standard (7CFR 205.203) to maintain or improve natural

resources including soil and water quality (7CFR 205.602) (OMRI, 2016). As a

supplemental source of N nutrition, it is still not widely adopted by organic growers due

to concerns such as that excessive sodium residue may damage the soil structure.

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Although the comparisons between organic and conventional fertilizers on

vegetable and fruit production have been studied in the past, updated research

information regarding organic fertilizers derived from various N sources is limited. In this

greenhouse study, the effects of fertilizers from different nutrient sources on strawberry

growth, yield, and fruit quality were examined.

Materials and Methods

Experimental Design and Greenhouse Strawberry Production

This experiment was carried out during the 2014-2015 strawberry season in a

greenhouse on the University of Florida campus, Gainesville, FL (lat. 29.64˚N, long.

82.35˚W). The soil (classified as Candler sand) used in this study was from a certified

organic field in Citra, FL. Three organic fertilizers including Jobe’s Organics Bone Meal

2N-6.1P-0K (Easy Gardener Products, Inc., Waco, TX), MicroSTART60 3N-0.9P-2.5K

(Perdue AgriRecycle, LLC., Seaford, DE), and Meat & Bone meal 7N-5.2P-0K (Howard

Fertilizer & Chemical Co., Inc., Orlando, FL) were mixed at the ratio of 1:1:1 (w/w/w)

and then incorporated into the soil as preplant fertilizer, which accounted for

approximately 20% (33.6 kg/ha) of the total N required for strawberry production based

on the N fertilization recommendation for Florida strawberry production (Santos et al.,

2012). An identical amount of preplant fertilizer (11.6 g) was mixed into each pot before

transplanting the strawberry plants. Strawberry plug transplants (Luc Lareault Nursery,

Quebec, Canada) were planted into the black plastic pots (7.6 L) on 30 Oct. 2014 with

one plant in each pot. All the pots were placed on the benches inside a greenhouse with

an average air temperature of 20.4˚C.

The experiment was arranged in a randomized complete block design with 4

blocks/replications and 12 plants per treatment per replication. There were 6 treatment

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combinations consisting of 2 strawberry cultivars and 3 fertilizer treatments. The two

strawberry cultivars included SensationTM ‘Florida127’ and WinterstarTM ‘FL 05-107’,

which were released from the University of Florida strawberry breeding program in 2013

and 2011, respectively. ‘Florida127’ was bred with a focus on good flavor while ‘FL 05-

107’ is an early cultivar with the ability to adapt winter plasticulture growing systems

(Whitaker et al., 2012; Whitaker et al., 2015). The three fertilizer treatments (Table 4-1)

were: 1) Howard Organic [GATOR 96002 Organic Liquid 3N-0P-5.0K (Howard Fertilizer

& Chemical Co., Inc., Orlando, FL)], 2) Neptune Organic [Neptune’s Harvest Fish

Fertilizer 2N-0P-1.7K (Neptune’s Harvest, Gloucester, MA) with Potassium Sulfate 0N-

0P-41.5K (Compass Minerals, Overland Park, KS)], and 3) Mayo Conventional [Mayo

Fertilizer 6N-0P-6.6K (Mayo fertilizer, Inc., Lee, FL) with Potassium Chloride 0N-0P-

49.8K (Potash Corp, Northbrook, IL)]. All the fertilizers were applied through a

fertigation system. Soil testing prior to this study showed a high level of soil P2O5.

Therefore, the three fertilizer treatments in this study did not contain P. All three fertilizer

treatments had a N:K ratio of 1:1.7. Fertilizer application took place twice a day at 200

mg/L N, 1-3 min each event based on the weather, through a fertigation system

equipped with four Dosatron injectors (Dosatron, Clearwater, FL) from 29 Nov. 2014 (29

DAT) till the end of the experiment (11 May 2015, 192 DAT). A single pressure-

compensation drip emitter with a flow rate of 2 L/h was used for each plant. The total

amount of N, P, and K applied during the season was 6.8, 7.0, and 7.5 g on a per plant

basis for each fertilizer treatment. To address poor pollination in the greenhouse, an

electric pollinator – “Petal Tickler” Ultima Pollinator (Progressive Solutions, Shreve, OH)

and ventilation fans were used during flowering to facilitate pollination. Predatory mites

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Phytoseiulus persimilis and Neoseiulus californicus (Spidex and Spical; Koppert

Biological Systems, Inc., Howell, MI) were released on 19 Nov. 2014 to control

twospotted spider mites.

Soil and Tissue Analyses

Soil samples were collected at the depth of 30 cm in the field for nutrient analysis

before planting strawberry (16 Oct. 2014) and analyzed by Waters Agricultural

Laboratories, Inc., Camilla, GA. The fertilization rates, including preplant application and

fertigation were developed based on the soil test results and the fertilization

recommendation for Florida strawberry production. A soil health test was conducted

only on soil from pots with ‘Florida127’ after final harvest (28 Apr. 2015) by Woods

End® Laboratories, Inc., Mt Vernon, ME. The soil health score (0-35) was calculated

based on several measurements of soil biological properties including respiration of

CO2-C (aggregate microbial activity), total water soluble C (quantity of organic C

extractable by water), solvita labile amino-N (N present in the alkaline extract of the

soil), and aggregate stability (soil textural quality) (Woods End® Laboratories, 2016).

Strawberry leaf tissue nutrient analysis was conducted at the early stage (26 Nov. 2014,

26 DAT), middle season (15 Jan. 2015, 76 DAT), and late season (20 Apr. 2015, 171

DAT) using 14 of the most recently matured leaves by Waters Agricultural Laboratories,

Inc., Camilla, GA.

Plant Growth Assessment

Plants with open flowers were counted on 24 Nov. and 1 Dec. 2014 and runners

were removed on 1 Dec., 6 Dec., 16 Dec., 26 Dec., 31 Dec. 2014 and 20 Jan. 2015.

Plant growth parameters including leaf number, canopy size, crown diameter, and

chlorophyll content index were measured at early stage (25 Nov. 2014, 25 DAT), peak

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harvest (9 Jan. 2015, 70 DAT), and late season (20 Apr. 2015, 171 DAT). The above-

and below-ground biomass amounts were evaluated on 11 May 2015 (192 DAT) after

the final harvest.

Strawberry Yield Evaluation

Strawberry harvests were carried out from 16 Dec. 2014 (46 DAT) to 21 Apr.

2015 (172 DAT), with around four harvests conducted each month and 18 harvests in

total. Ripe strawberries with over 80% red color were picked with calyces attached. A

marketable strawberry was defined as over 5 g in weight and no signs of disease or

pest damage, decay or mechanical injury. Marketable and cull fruit were counted and

weighed to determine marketable and total yields, while unmarketable fruit were also

recorded by different categories: deformed, small, damage (due to pests and rodents),

rot (caused by botrytis and soft rot), and others. Marketable fruit were then sorted to

obtain samples of uniform size and color for fruit quality analysis.

Detailed procedures of strawberry growth and yield assessment were described

in Chapter 2.

Fruit Quality Evaluation

Fresh fruit quality parameters including color and firmness were evaluated on

fruit samples harvested on 16 Feb., 10 Mar., and 31 Mar. 2015 (108, 130, 151 DAT)

within 24 hours of harvest. Fruit external color was assessed using a chroma meter

(Model CR-400, Konica Minolta Sensing Americas, Inc., NJ) and expressed as C.I.E.

lightness, chroma, and hue (L*c*h*). Two color readings from the opposite sides of fruit

were recorded. Fruit firmness was measured using a hand-held penetrometer (Fruit

TestTM FT, Wagner Instruments, Greenwich, CT) with an 8 mm Magness-Taylor-type

probe and expressed as kg-force.

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Strawberry fruit for composition analyses including TSS, TA, TMA, TPC, and VC

were harvested on 11 Feb., 23 Feb., 10 Mar., and 31 Mar. 2015 (104, 116, 131, 152

DAT), kept at 1˚C and 95% relative humidity immediately after harvest, and frozen at

minus 20˚C within 24 hours of harvest until analysis. The detailed analysis protocols

were described previously in Chapter 3.

Statistical Analysis

Data analysis was performed using the Glimmix procedure of SAS statistical

software package for Windows (Version 9.2; SAS Institute, Cary, N.C.) according to the

RCBD used. Multiple comparisons were conducted following the two-way analysis of

variance (ANOVA), using Fisher’s Least Significant Difference (LSD) test at P ≤ 0.05.

Results and Discussion

Soil and Strawberry Leaf Tissue Analyses

Soil nutrient and health tests conducted after the strawberry final harvest

demonstrated interesting results. ‘Florida127’ plants fertilized with Neptune Organic

treatment had significantly higher soil health scores (12.58) than ‘Florida127’ with Mayo

Conventional (5.38) and Howard Organic (5.18) treatments, whereas Na level in

Howard Organic treated soil was much higher than in the other two treatments. N, P,

and K availability in all treatments were medium or high (Data not shown).

In terms of strawberry leaf tissue analysis, fertilizer treatments demonstrated

marked effects on nutrient levels of strawberry tissue at middle and late season, while

cultivars differed in Mg and Fe at 76 DAT (15 Jan. 2015) as well as Ca and Mn at 171

DAT (20 Apr. 2015), with fertilizer x cultivar interactions for P and Mn at 171 DAT (20

Apr. 2015) (Table 4-2). Fertilizer treatments differed in P, Mn, Zn, Cu, and B contents at

76 DAT (20 Apr. 2015), as well as levels of most of the analyzed elements except Fe

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and Cu at 171 DAT (20 Apr. 2015) (Table 4-2). Strawberry fertilized with Neptune

Organic consistently showed higher levels of P and Mn, while Howard Organic

treatment produced strawberries with lower Mn and Zn content in the leaf tissue

compared with the other fertilizer treatments at both 76 and 171 DAT (15 Jan. and 20

Apr. 2015) (Table 4-2). Interestingly, B level was found to be the highest under Mayo

Conventional treatment while it did not differ between the other two organic fertilizer

treatments at either 76 or 171 DAT (15 Jan. and 20 Apr. 2015) (Table 4-2). Neptune

Organic treated strawberry also had higher levels of N and Ca than Howard Organic

grown strawberry in late season but it did not differ significantly from Mayo

Conventional, while it showed higher levels of Mg and S with no differences between

the other two fertilizer treatments (Table 4-2). In contrast, plants fertilized with Howard

Organic exhibited higher levels of K in late season with no differences detected between

the other two fertilizer treatments (Table 4-2). ‘Florida127’ had higher levels of Mg and

Fe at 76 DAT (15 Jan. 2015) and also higher Ca and Mn contents at 171 DAT (20 Apr.

2015) (Table 4-2). The tissue analysis results at early season indicated that plants were

adequate in N, Ca, Mg, S, Fe, Mn, Zn, B and Cu, high in P and K, according to Santos

et al. (2012).

Plant Growth

Leaf number and crown diameter of strawberry plants differed between cultivars

at 25 DAT (25 Nov. 2014), while fertilizer treatments had influence on leaf number,

canopy size, and crown diameter at 171 DAT (20 Apr. 2015). Strawberry plants grown

with Howard Organic had fewer leaf count than Neptune Organic treatment, whereas

both organic fertilizer treatments did not differ from Mayo Conventional treatment;

Neptune Organic resulted in bigger canopy size while Howard Organic did not differ

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from Mayo Conventional in terms of canopy size; smaller crown diameter was observed

in Howard Organic treatment, whereas no differences were detected between Mayo

Conventional and Neptune Organic treatments at 171 DAT (20 Apr. 2015) (Table 4-3).

‘Florida127’ had more leaves per plant whereas ‘FL 05-107’ had larger crowns at 25

DAT (25 Nov. 2014) (Table 4-3). Cultivar by fertilizer interaction was also found in leaf

number and canopy size such that Mayo Conventional fertilized ‘FL 05-107’ had more

leaf counts than strawberry plant fertilized with Howard Organic, but ‘Florida127’ with

Mayo Conventional presented lowest leaf count; Howard Organic fertilized ‘Florida127’

had larger canopy than Mayo Conventional treatment but Howard Organic fertilized ‘FL

05-107’ produced smallest canopy size (Data not shown). Except for the higher value in

‘Florida127’ than ‘FL 05-107’ at 171 DAT (20 Apr. 2015), cultivars or fertilizer treatments

did not differ significantly in leaf chlorophyll content index (Table 4-3). At 70 DAT (9 Jan.

2015), ‘FL 05-107’ presented bigger canopy than ‘Florida127’ (Table 4-3). ‘FL 05-107’

had more plants with open flowers and more runner counts than ‘Florida127’ in Nov.

and Dec. 2014 cumulatively, whereas plants fertilized with Neptune Organic had lowest

below-ground biomass at the end of the season (Data not shown).

Fruit Yield

With respect to whole season fruit yield, the two strawberry cultivars differed in

both marketable and total fruit yields, whereas the only difference among fertilizer

treatments was found in total fruit number per plant (Table 4-4). ‘Florida127’

demonstrated higher marketable and total fruit yields, as well as greater average

marketable fruit weight, while ‘FL 05-107’ had higher total fruit number per plant (Table

4-4). Strawberries fertilized with Neptune Organic exhibited greater total fruit number

per plant in comparison with the other two fertilizer treatments (Table 4-4). In terms of

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monthly yields, cultivar effects were more consistent than fertilizer impacts throughout

the harvest season. Both marketable and total fruit number and yields of the two

cultivars increased from Jan. to Apr. 2015; however, it was surprising that fruit number

and yield tended to decrease from Dec. 2014 to Jan. 2015 (Figures 4-1 and 4-2).

‘Florida127’ showed higher marketable and total fruit numbers in Feb. 2015, while ‘FL

05-107’ exhibited higher total fruit numbers in Mar. and Apr. 2015, as well as greater

numbers of marketable and total fruit in Dec. 2015 (Figure 4-1). ‘Florida127’

demonstrated significantly higher marketable and total fruit yields per plant compared

with ‘FL 05-107’ from Feb. to Apr. 2015; however, no differences were observed in fruit

yield between cultivars in Dec. 2014 and Jan. 2015 (Figure 4-2). The average weight of

marketable ‘Florida127’ fruit was significantly higher than ‘FL 05-107’ throughout the

season (data not shown). With regards to fertilizer impact on monthly yields, strawberry

plants fertilized with Neptune Organic had higher total fruit yield per plant than plants

fertilized with Howard Organic in Dec. 2014, while Howard Organic treatment resulted in

lower total fruit yield than other two fertilizer treatments in Mar. and Apr. 2015 (Figure 4-

3). As for unmarketable fruit yield during the season, no cultivar or fertilizer effects were

found; however, ‘FL 05-107’ had higher cull percentage of small fruit but lower cull

percentage of fruit with Botrytis than ‘Florida127’ (Figure 4-4).

The results demonstrated pronounced cultivar effects on strawberry yield.

‘Florida127’ showed higher marketable and total yields, while ‘FL 05-107’ demonstrated

early yielding with greater marketable and total fruit numbers in Dec. 2014. As the

season progressed, ‘FL 05-107’ was lower in fruit yield during Feb.–Apr. 2015. The

lower total fruit yield but greater total fruit number of ‘FL 05-107’ was likely attributed to

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the smaller size of fruit as compared with ‘Florida127’ (Table 4-4). Overall, ‘Florida127’

demonstrated better yield performance under organic fertilization in this study. The

larger fruit size of ‘Florida127’ would probably make the fruit more appealing in the

marketplace and might save some harvest labor as the strawberry fruit are sold by

weight. However, ‘FL 05-107’ might be more resistant to Botrytis (Figure 4-4), a

common strawberry fugal disease affecting fruit yield and quality. Whitaker et al. (2012)

indicated that the relative susceptibility to Botrytis is ‘Strawberry Festival’ > ‘FL 05-107’

> ‘Camino Real’. In addition, ‘Florida127’ may be more vulnerable to Botrytis than

‘Florida Radiance’ (Whitaker et al., 2014). Organic and conventional fertilizer treatments

did not differ in terms of strawberry marketable yield, which concurred with the findings

reported by Hargreaves et al. (2008) and Herencia et al. (2007) that yields of strawberry

and multiple other crops were not affected differentially by organic and conventional

fertilizers. However, it was not consistent with results of others that organically grown

strawberry was lower in vegetative and reproductive development as well as marketable

fruit yield than conventional strawberry (Gliessman et al., 1996).

Fruit Quality

The differences in fruit color between cultivars tended to occur towards the end

of the season. ‘Florida127’ fruit generally had higher L, C, and H values than ‘FL 05-

107’ especially at 151 DAT (31 Mar. 2015), indicating lighter, brighter, and less red

external color for ‘Florida127’ (Table 4-5). Cultivar did not show any effects on fruit

firmness but fertilizer treatments differed significantly in fruit firmness at harvest at 151

DAT (31 Mar. 2015). Howard Organic treatment enhanced strawberry firmness while

strawberries fertilized with Mayo Conventional were the softest (Table 4-5).

78

In terms of fruit composition, neither cultivar nor fertilizer treatments exhibited

any significant influence on VC from 103 to 151 DAT (11 Feb.–31 Mar. 2015) (Table 4-

6). Fertilizer effects appeared mostly in TSS from 103 to 130 DAT (11 Feb.–10 Mar.

2015), with Howard Organic promoting higher fruit TSS content compared with Neptune

Organic or Mayo Conventional treatments. The cultivar effects were primarily in pH from

103 to 130 DAT (11 Feb.–10 Mar. 2015) with ‘FL 05-107’ showing significantly higher

pH than ‘Florida127’ (Table 4-6). The only fertilizer and cultivar interaction was found in

TPC at 115 DAT (23 Feb. 2015): Mayo Conventional fertilization showed the higher

TPC among other fertilizer treatments in the case of ‘FL 05-107’, but TPC was the

lowest with Mayo Conventional in ‘Florida127’ (Data not shown). Fertilizer treatments

demonstrated significant impacts on TA and TPC at 130 DAT (10 Mar. 2015) as well as

TPC at 103 DAT (11 Feb. 2015). Howard Organic grown strawberries had higher TA

than the other two fertilizer treatments, while the two organic fertilizer treatments

showed higher levels of TPC than that of Mayo Conventional at 103 DAT (Table 4-6). At

130 DAT (10 Mar. 2015), Howard Organic resulted in an elevated level of TPC than

Mayo Conventional. Cultivar showed some effects in TSS, TA, and TPC with

‘Florida127’ fruit containing higher levels of TSS, TA, and TPC at 130 DAT but a lower

level of TMA at 151 DAT (31 Mar. 2015) in comparison with ‘FL 05-107’ (Table 4-6).

Strawberry fruit pH ranged from 3.6 to 4.0 with a declining trend over time. Strawberries

at 130 DAT (10 Mar. 2015) appeared to have lower TSS level compared with other

sampling dates (Table 4-6).

To date, some studies have indicated that organic substances derived from

diverse sources help promote crop growth and yield, while the effects are dose sensitive

79

(Atiyeh et al., 2002; Schulz and Glaser, 2012; Togun and Akanbi, 2003; Valdrighi et al.,

1996), and vary by plant part (Atiyeh et al., 2002; Chen and Aviad, 1990) as well as

sampling time (Liu et al., 2009). The observed effects of fertilizers from different N

sources could be explained by different nutrient-retention capacity of ingredients, in

addition to influence on soil quality and N mineralization and uptake dynamics as a

whole. Combining organic amendments from various sources with inorganic fertilizer

has been reported to enhance soil microbial population, organic C, and nutrient

availability (Barzegar et al., 2002; Hao et al., 2008; Herencia et al., 2007; Liu et al.,

2009; Nayak et al., 2007; Schulz and Glaser, 2012; Zhong and Cai, 2007), therefore

improving crop growth and yield (Ayoola and Makinde, 2007; Akanbi and Togun, 2002).

Organic nutrient sources of different ingredients from animal, plant, or mineral based

materials might have differential influence on N dynamics, such as mineralization rate of

organic matter, leaching rate of NO3-, and nitrification rate. The N mineralization from

organic substances might not meet crop N uptake needs during the peak demand

period, thus leading to reduced plant growth and fruit yield (Pang and Letey, 2000).

Muramoto et al. (2004) indicated that in total approximately 120 kg/ha N was absorbed

by strawberry plants and most of the uptake happened later in the season. Gagnon and

Berrouard (1994) demonstrated that organic fertilizers derived from blood, feathers,

meat, crab shells, fish, and cottonseed had positive effects on shoot biomass of tomato

transplants, whereas the fertilizers derived from vegetation including alfalfa, canola, and

wheat bran had no or negative effects on tomato growth compared with the without

fertilizer control. Rathore et al. (2009) found that seaweed extract promoted N, P, and K

uptake in soybean and plants were significantly taller with 10-15% seaweed extract

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application. Togun and Akanbi (2003) reported that compost from maize (Zea mays L.),

guinea grass (Panicum maximum Jacq.), and cowpea (Vigna unguiculata L.) resulted in

various tomato plant growth and yield performance but more favorable than chemical

fertilizer alone in general. Soumare et al. (2003) indicated that municipal solid waste

compost with mineral fertilizer application increased ryegrass (Lolium perenne L.) yield.

Vigorous strawberry plant growth in Neptune Organic treatment towards the end of the

season was supported by Arancon et al. (2004 b) that humic acid fertilizer resulted in

better strawberry plant growth. It can also be explained by stress alleviation as a result

of using seaweed extract. Plant amended with seaweed extracts showed enhanced

tolerance to extreme temperature in grape (Vitis vinifera L.) and winter barley (Hordeum

vulgare L.) (Burchett et al., 1998; Mancuso et al., 2006). Continuous events of high

temperature (over 32˚C) occurred during the late season in greenhouse conditions,

which may inhibit strawberry plant growth in Howard Organic and Mayo Conventional

treatments, while Neptune Organic containing seaweed extract help mitigating high

temperature stress.

Research-based information on strawberry quality as affected by organic

fertilizers derived from various sources is limited. In the present study, strawberry grown

with organic or conventional fertilizers had similar levels of fruit pH, VC, and total

anthocyanins. The organic fertilizer consisting of NaNO3 and K2SO4 from natural deposit

showed a tendency to enhance fruit soluble solids content, and to a lesser extent a

tendency to increase titratable acidity. Higher total phenolic content in strawberry fruit

was also observed in the two organic fertilizer treatments from one of the Feb. harvests

compared with the conventional fertilizer. Some previous studies demonstrated fruit

81

quality improvement in some organically grown crops in contrast to the conventional

counterpart such as higher vitamin C content in of vegetables, fruits, and grains

(Reganold et al, 2010; Worthington, 2001), higher total antioxidant activity and total

phenolics in tomato, strawberry, and other horticultural crops (Abu-Zahra et al., 2006;

Asami et al., 2003; Mitchell et al., 2007; Olsson et al., 2006; Reganold et al, 2010;

Wang et al., 2008), and longer shelf-life and preferable sensory properties (Reganold et

al, 2010). On the other hand, some indicated that organic fertilizers or amendments did

not affect strawberry fruit quality, such as total phenolics (Häkkinen and Törrönen,

2000), or sugar and total antioxidant capacity (Hargreaves et al., 2008). Humic acids

were found to improve nutrient use efficiency and enhance strawberry fruit quality by

increasing sugar content (Ameri and Tehranifar, 2012; Neri et al., 2002). Strawberry had

significant higher TSS content when receiving humic acid or vermicompost than mineral

fertilizer treatment (Azarmi et al., 2009; Farahi et al., 2013; Gharib et al., 2011), which is

inconsistent with the results from our study that TSS content was not elevated by

Neptune Organic compared with Mayo Conventional.

Conclusions

In this study, the two types of organic fertilizers from different sources did not

differ greatly from the conventional fertilizer in terms of strawberry fruit yield; however,

plants fertigated with the organic fertilizer containing sea weed extract showed more

vigorous growth at the end of the production season. Fruit total soluble solids, titratable

acidity, and total phenolic content were affected by the fertilizer treatments with the

greater impact shown in total soluble solids. Neptune Organic improved soil health

greatly considering soil microbial activity, textural quality, organic C and N as a whole.

Overall, strawberry cultivar exhibited more influence than fertilizer treatment on fruit

82

yield and quality attributes. It is likely that sodium nitrate will be completely prohibited in

organic production in the near future and other soluble organic fertilizer options for in-

season fertigation will need to be explored towards meeting crop nutrient demand and

improving crop and soil quality.

83

Table 4-1. Ingredients and N-P-K composition of three fertilizer treatments for in-season fertigation for strawberry production.

Treatment name Fertilizers

Grade (N-P-K) % Ingredients

Howard Organic

GATOR 96002/3-0-6 0-0 Organic Liquid

3-0-5.0 Derived from organic sulfate of potash, sodium nitrate

Neptune Organic

Neptune’s Harvest Fish Fertilizer

2-0-1.7 Hydrolyzed fish, molasses, seaweed, humate, and yucca extract

Potassium Sulfate 0-0-41.5

Mayo conventional

Mayo Fertilizer 6-0-6.6 Derived from ammonium nitrate, calcium nitrate, disodium octaborate, magnesium nitrate solution, potassium nitrate, urea nitrate, muriate of potash, and zinc sulfate

Potassium Chloride 0-0-49.8

84

Table 4-2. Fertilizer and cultivar effects on nutrient concentration of most recently mature leaves at early stage (26 DAT), middle season (76 DAT), and late season (171 DAT).

Early stage

N P K Ca Mg S Fe Mn Zn Cu B Treatment (%) (%) (%) (%) (%) (%) (ppm) (ppm) (ppm) (ppm) (ppm)

Cultivar Florida127 3.17 0.64 2.58 1.03 0.43 0.19 80 47 32 4.7 37 FL 05-107 3.25 0.52 2.57 1.09 0.33 0.19 78 118 43 5.7 22

Middle season Fertilizer

MC 3.01 0.41bz 2.61 1.38 0.51 0.14 73 67b 18a 4.3 67a HO 3.08 0.44b 2.59 1.47 0.56 0.13 68 45c 14b 3.6 27b NO 2.97 0.85a 2.67 1.43 0.53 0.14 67 148a 17a 4.0 29b Significancey NS *** NS NS NS NS NS *** ** NS ***

Cultivar Florida127 3.07 0.55 2.58 1.57a 0.58a 0.13 73a 85 17 3.9 43 FL 05-107 2.97 0.58 2.66 1.29b 0.48b 0.13 66b 88 16 4.0 39 Significance NS NS NS * * NS * NS NS NS NS

F x C interaction NS NS NS NS NS NS NS NS NS NS NS Late season Fertilizer

MC 2.22ab 0.16b 2.51b 1.54a 0.38b 0.19b 59 135b 20a 5.3 133a HO 1.99b 0.15b 2.80a 1.14b 0.35b 0.19b 55 19c 14b 4.1 26b NO 2.46a 0.66a 2.58b 1.45a 0.47a 0.39a 60 291a 21a 4.0 21b Significance * *** * *** *** *** NS *** *** NS ***

Cultivar Florida127 2.25 0.32 2.61 1.47a 0.40 0.26 58 161a 19 4.2 62 FL 05-107 2.19 0.33 2.65 1.28b 0.40 0.25 58 134b 18 4.8 58 Significance NS NS NS ** NS NS NS ** NS NS NS

F x C interaction NS ** NS NS NS NS NS ** NS NS NS

MC: Mayo Conventional; HO: Howard Organic; NO: Neptune Organic; N: Nitrogen; P: Phosphorus; K: Potassium; Ca: Calcium; Mg: Magnesium; S: Sulfur; Cu: Copper; Fe: Iron; Mn: Manganese; Zn: Zinc. z Means within the same column followed by the same letter do not differ significantly by Fisher’s least significant difference test at P ≤ 0.05. y NS, *, **, *** Nonsignificant or significant at P ≤ 0.05, 0.01, or 0.001, respectively.

85

Table 4-3. Fertilizer and cultivar effects on strawberry growth parameters at 25, 70, and 171 DAT throughout the production season.

z Means within the same column followed by the same letter do not differ significantly by Fisher’s least significant difference test at P ≤ 0.05. y NS, *, **, *** Nonsignificant or significant at P ≤ 0.05, 0.01, or 0.001, respectively.

Leaf number per plant

Canopy size (cm)

Crown diameter (mm) Chlorophyll content index

(SPAD value)

Treatment 25 DAT 70 DAT 171 DAT 25 DAT 70 DAT 171 DAT 25 DAT 70 DAT 171 DAT 25 DAT 70 DAT 171 DAT

Fertilizer

MC 3.0 10.5 21.5ab 17.2 37.2 27.6b 12.1 21.5 49.7a 43.8 50.4 54.5

HO 2.9 10.9 20.1b 17.7 36.2 27.2b 12.1 22.2 38.8b 43.4 51.0 54.4

NO 3.1 11.5 24.0a 18.9 37.9 30.5a 12.2 22.4 46.2a 43.9 50.2 54.3

Significancey NS NS * NS NS ** NS NS ** NS NS NS

Cultivar

Florida127 3.2az 11.4 21.3 17.6 36.2b 29.1 11.7b 22.5 46.4 43.7 50.4 55.2a

FL 05-107 2.9b 10.5 22.4 18.3 37.9a 27.8 12.6a 21.5 43.4 43.6 50.6 53.6b

Significance ** NS NS NS * NS * NS NS NS NS *

F x C interaction NS NS ** NS NS * NS NS NS NS NS NS

86

Table 4-4. Fertilizer and cultivar effects on total and marketable strawberry yields during the production season.

Marketable fruit number

Marketable fruit yield

Total fruit number

Total fruit yield

Average marketable fruit weight

Cull percentage

(%) Treatment (no./plant) (g/plant) (no./plant) (g/plant) (g/fruit)

Fertilizer MC 15.4 275.6 22.9 bz 349.8 17.9 21.5 HO 16.0 255.1 23.4 b 328.5 16.0 22.4 NO 17.4 296.9 26.0 a 377.9 17.3 21.8 Significancey NS NS * NS NS NS Cultivar

Florida127 15.9 312.7 a 23.0 b 395.4 a 19.7 a 21.1 FL 05-107 16.6 239.1 b 25.2 a 308.7 b 14.4 b 22.7

Significance NS *** * *** *** NS F x C interaction NS NS NS NS NS NS

MC: Mayo Conventional; HO: Howard Organic; NO: Neptune Organic.

z Means within the same column followed by the same letter do not differ significantly by Fisher’s least significant difference test at P ≤ 0.05. y NS, *, **, *** Nonsignificant or significant at P ≤ 0.05, 0.01, or 0.001, respectively.

87

Table 4-5. Fertilizer and cultivar effects on strawberry fruit color and firmness at 108, 130, 151 DAT (16 Feb., 10 Mar., and 31 Mar. 2015) throughout the production season.

Quality attributes DAT

Fertilizer Cultivar M x C interactiony MC HO NO Florida127 FL 05-107

L*

108 40.26 40.76 42.28 42.76 39.44 NS

130 38.79 38.56 38.56 39.56 az 37.72 b NS

151 36.24 37.04 36.61 38.20 a 35.06 b NS

C*

108 53.30 53.35 51.98 53.84 51.92 NS

130 36.07 35.42 35.96 35.55 36.08 NS

151 41.74 45.70 43.38 45.63 a 41.58 b NS

H*

108 40.08 39.04 40.39 40.80 38.87 NS

130 27.13 25.58 25.89 26.32 26.08 NS

151 32.30 33.84 32.98 33.98 a 32.09 b NS

Firmness (kg-force)

108 0.66 0.73 0.66 0.65 0.71 NS

130 0.55 0.56 0.49 0.51 0.55 NS

151 0.47 b 0.60 a 0.51 ab 0.52 0.54 NS

DAT: Days After Transplanting; MC: Mayo Conventional; NO: Neptune Organic; HO: Howard Organic. z Means within the same column followed by the same letter do not differ significantly by Fisher’s least significant difference test at P ≤ 0.05. y NS, *, **, *** Nonsignificant or significant at P ≤ 0.05, 0.01, or 0.001, respectively.

88

Table 4-6. Fertilizer and cultivar effects on strawberry compositional quality attributes at

104, 116, 131, 152 DAT (11 Feb., 23 Feb., 10 Mar., and 31 Mar. 2015) throughout the production season.

Quality attributes DAT

Fertilizer Cultivar M x C interactiony MC HO NO Florida127 FL 05-107

TSS (% soluble solids)

104 9.7 b 10.8 az 10.2 ab 10.1 10.4 NS

116 11.0 ab 11.8 a 10.8 b 11.3 11.1 NS

131 7.3 b 8.2 a 7.5 b 8.1 a 7.3 b NS

152 10.1 10.1 9.6 10.1 9.7 NS

TA (% citric acid)

104 0.71 0.75 0.68 0.73 0.70 NS

116 0.74 0.77 0.68 0.76 0.71 NS

131 0.65 b 0.81 a 0.60 b 0.73 a 0.65 b NS

152 0.81 0.91 0.82 0.84 0.86 NS

pH

104 3.90 3.92 3.97 3.86 b 4.00 a NS

116 3.73 3.83 3.78 3.71 b 3.85 a NS

131 3.67 3.63 3.71 3.61 b 3.73 a NS

152 3.66 3.68 3.63 3.63 a 3.68 a NS

TMA (mg/100 g FW)

104 2.16 2.28 1.82 1.81 2.37 NS

116 2.82 3.02 2.46 2.44 3.09 NS

131 1.95 2.19 1.95 1.95 2.12 NS

152 3.37 3.46 2.76 2.61 b 3.78 a NS

TPC (mg GAE/g FW)

104 1.74 b 1.91 a 1.94 a 1.82 1.91 NS

116 2.42 2.63 2.83 2.57 2.68 *

131 1.59 b 1.80 a 1.71 ab 1.77 a 1.63 b NS

152 1.90 2.26 2.21 1.98 2.26 NS

VC (mg/100 g FW)

104 39.0 39.7 44.0 39.4 42.4 NS

116 38.6 40.1 40.4 40.5 38.8 NS

131 36.0 36.4 36.6 38.2 34.5 NS

152 37.5 35.7 38.0 37.6 36.5 NS

DAT: Days After Transplanting; MC: Mayo Conventional; NO: Neptune Organic; HO: Howard Organic. z Means within the same column followed by the same letter do not differ significantly by Fisher’s least significant difference test at P ≤ 0.05. y NS, *, **, *** Nonsignificant or significant at P ≤ 0.05, 0.01, or 0.001, respectively.

89

Figure 4-1. Marketable and total fruit numbers of ‘Florida127’ and ‘FL 05-107’ by month

during production season from Dec. 2014 to Apr. 2015. S: ‘Florida127’; W: ‘FL 05-107’; MFN: Marketable Fruit Number; TFN: Total Fruit Number. Values for each month period followed by the same upper or lower case letter do not differ significantly by Fisher’s least significant difference test at P ≤ 0.05. Upper case letters represent comparisons in total fruit number per plant between cultivars, lower case letters represent comparisons in marketable fruit number per plant between cultivars.

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

16.0

18.0

Dec Jan Feb Mar-Apr

Fru

it n

um

be

r/p

lan

t

Harvest month

S MFN

S TFN

W MFN

W TFN

B

a

a A

B

A

B

a

b

a

A

A

A

a a

b

90

Figure 4-2. Marketable and total fruit yields of ‘Florida127’ and ‘FL 05-107’ by month

during production season from Dec. 2014 to Apr. 2015. S: ‘Florida127’; W: ‘FL 05-107’; MFW: Marketable Fruit Weight; TFW: Total Fruit Weight. Values for each month period followed by the same upper or lower case letter do not

differ significantly by Fisher’s least significant difference test at P ≤ 0.05.

Upper case letters represent comparisons in total fruit weight per plant between cultivars, lower case letters represent comparisons in marketable fruit weight per plant between cultivars.

0.0

50.0

100.0

150.0

200.0

250.0

Dec Jan Feb Mar-Apr

g/p

lan

t

Harvest month

S MFW

S TFW

W MFW

W TFW

A A

a a

A

B

a

b

A

B

a

b

A A a

a

91

Figure 4-3. Marketable and total fruit yields of three fertilizer treatments by month during

production season from Dec. 2014 to Apr. 2015. MC: Mayo Conventional; HO: Howard Organic; NO: Neptune Organic; MFW: Marketable Fruit Weight; TFW: Total Fruit Weight. Values for each month period followed by the same letter do not differ significantly by Fisher’s least significant difference test at P

≤ 0.05. No letter indicates no significant differences.

0

50

100

150

200

250

Dec Jan Feb Mar-Apr

MC MFW 27.6 15.3 87.9 144.8

HO MFW 22.9 17.1 74.6 140.5

NO MFW 28.8 14.6 86.8 166.6

MC TFW 35.7 24.5 107.3 182.3

HO TFW 28.3 25.9 98.1 176.1

NO TFW 46.6 23.5 106.5 207.3

g/p

lant

b

a

ab

b

ab

a

92

Figure 4-4. Classifications and percentage of strawberry cull fruit weight among all

treatments during Dec. 2014 – Apr. 2015 production season. MC: Mayo Conventional; NO: Neptune Organic; HO: Howard Organic.

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

MC NO HO MC NO HO

Cull

pe

rcen

tage

Florida127

Deformed Botrytis Insect Damage Rodent Soft Rot Small other

FL 05-107

93

CHAPTER 5 SUMMARY

The findings from the present study indicate that growing sunn hemp during the

summer off-season before the fall planting of strawberry does not show any promoting

effects on plant growth and fruit yield. Compared with the summer fallow control using

the same amount of fertilization for strawberry production, the sunn hemp treatment

actually reduced the marketable and total fruit numbers and weight in December. When

nutrient release from sunn hemp was considered and preplant fertilization was reduced,

the sunn hemp treatment further decreased the full season total fruit number and

weight. In contrast, the sunn hemp treatments did not exhibit any consistent adverse

impacts on strawberry fruit quality attributes including color, firmness, total soluble

solids, titratable acidity, pH, total anthocyanins, total phenolics and vitamin C, as well as

consumer perceived sensory properties and postharvest quality during shelf life.

Organic fertilizers from diverse sources had little influence on strawberry yield although

plants fertigated with the organic fertilizer containing sea weed extract showed more

vigorous growth at the end of the production season. Greater fertilizer effects were

found in fruit quality attributes particularly total soluble solids, titratable acidity, and total

phenolic content. In both the sunn hemp field study and the organic fertilizer

greenhouse experiment, strawberry cultivars demonstrated more pronounced effects

than nutrient management in terms of plant growth, yield, and fruit quality.

The dynamic of nutrient release from sunn hemp when it is in rotation with

strawberry grown in sandy soils in Florida is still unclear and more in-depth studies are

warranted to obtain a better understanding of the nutrient contribution from sunn hemp

to benefit organic strawberry nutrient management and crop performance. Nutrient

94

needs of crops vary during different growth and development stages. Hence, matching

nutrient supply with crop need is the key to optimizing crop yield potential. Long-term

effects of cover crops need to be measured in order to elucidate the impacts of summer

legumes on plant growth and yield performance of strawberry under organic production.

More studies are warranted to optimize soil fertility and nutrient management for organic

strawberry when cover crops are integrated into the cropping system. More research is

also needed to develop recommendations for efficient and cost-effective use of organic

fertilizers and amendments to enhance long-term sustainability of organic strawberry

production.

95

LIST OF REFERENCES

Abu-Zahra, T.R., K. Al-Ismail, and F. Shatat. 2006. Effect of organic and conventional systems on fruit quality of strawberry (fragaria× ananassa Duch.) grown under plastic house conditions in the Jordan Valley. I International Symposium on Fresh Food Quality Standards: Better Food by Quality and Assurance 741:159-171.

Adani, F., P. Genevini, P. Zaccheo, and G. Zocchi. 1998. The effect of commercial humic acid on tomato plant growth and mineral nutrition. Journal of Plant Nutrition 21:561-575.

Agehara, S. and D.D. Warncke. 2005. Soil moisture and temperature effects on nitrogen release from organic nitrogen sources. Soil Science Society of America Journal 69:1844-1855.

Akanbi, W.B. and A.O. Togun. 2002. The influence of maize–stover compost and nitrogen fertilizer on growth, yield and nutrient uptake of amaranth. Scientia Horticulturae 93:1-8.

Ali, S.G. and A. Rab. 2016. Effect of potash application on the growth and yield of tomato crop grown in saline condition. Pure and Applied Biology 5:287.

Ameri, A., A. Tehranifar. 2012. Effect of humic acid on nutrient uptake and physiological characteristic Fragaria ananassa var: Camarosa. Journal of Biodiversity and Environmental Sciences 6:77–79.

Arancon, N.Q., C.A. Edwards, P. Bierman, C. Welch, and J.D. Metzger. 2004 a. Influences of vermicomposts on field strawberries: 1. Effects on growth and yields. Bioresource Technology. 93:145-153.

Arancon N.Q., S. Lee, C.A. Edwards, R. Atiyeh. 2004 b. Effects of humic acids derived from cattle, food and paper-waste vermicomposts on growth of greenhouse plants. Pedobiologia 47:741-744.

Aranganathan, L. and S.R.R. Rajasree. 2016. Bioconversion of marine trash fish (MTF) to organic liquid fertilizer for effective solid waste management and its efficacy on tomato growth. Management of Environmental Quality 27:93-103.

Asami, D.K., Y.J. Hong, D.M. Barrett, and A.E. Mitchell. 2003. Comparison of the total phenolic and ascorbic acid content of freeze-dried and air-dried marionberry, strawberry, and corn grown using conventional, organic, and sustainable agricultural practices. Journal of Agricultural and Food Chemistry 51:1237-1241.

Atiyeh, R.M., S. Lee, C.A. Edwards, N.Q. Arancon, and J.D. Metzger. 2002. The influence of humic acids derived from earthworm-processed organic wastes on plant growth. Bioresource Trabechnology 84:7-14.

96

Avila, L., J. Scholberg, N. Roe, and C. Cherr. 2006. Can sunn hemp decrease nitrogen fertilizer requirements of vegetable crops in the Southeastern United States? HortScience 41:1005-1005.

Ayoola, O.T. and E.A. Makinde. 2007. Complementary organic and inorganic fertilizer application: influence on growth and yield of cassava/maize/melon intercrop with a relayed cowpea. Australian Journal of Basic and Applied Sciences 1:187-192.

Azarmi, R., M.T. Giglou, B. Hajieghrari. 2009. The effect of sheep-manure vermicompost on quantitative and qualitative properties of cucumber (Cucumis sativus L.) grown in the greenhouse. African Journal of Biotechnology 8:4953-4957.

Barzegar, A.R., A. Yousefi, and A. Daryashenas. 2002. The effect of addition of different amounts and types of organic materials on soil physical properties and yield of wheat. Plant and Soil 247:295-301.

Batte, M.T., N.H. Hooker, T.C. Haab, and J. Beaverson, 2007. Putting their money where their mouths are: consumer willingness to pay for multi-ingredient, processed organic food products. Food Policy 32:145-159.

Battino, M., J. Beekwilder, B. Denoyes-Rothan, M. Laimer, G.J. McDougall, B. Mezzetti. 2009. Bioactive compounds in berries relevant to human health. Nutrition Reviews 67:S145-S150.

Brennan, E.B. and R.F. Smith. 2005. Winter cover crop growth and weed suppression on the central coast of California. Weed Technology 19:1017-1024.

Burchett S., M.P. Fuller, A.J. Jellings. 1998. Application of seaweed extract improves winter hardiness of winter barley cv Igri. The Society for Experimental Biology 22–27.

Cabrera, M.L., D.E. Kissel, and M.F. Vigil. 2005. Nitrogen mineralization from organic residues. Journal of Environmental Quality 34:75-79.

Canellas, L.P., F.L. Olivares, N.O. Aguiar, D.L. Jones, A. Nebbioso, P. Mazzei, and A. Piccolo. 2015. Humic and fulvic acids as biostimulants in horticulture. Scientia Horticulturae 196:15-27.

Cantliffe, D.J., J.Z. Castellanos, and A.V. Paranjpe. 2007. Yield and quality of greenhouse-grown strawberries as affected by nitrogen level in coco coir and pine bark media. Proceedings of the Florida State Horticultural Society 120:157-161.

Capocasa, F., J. Scalzo, B. Mezzetti, and M. Battino. 2008. Combining quality and antioxidant attributes in the strawberry: The role of genotype. Food Chemistry 111:872-878.

97

Chen, Y. and T. Aviad, 1990. Effects of humic substances on plant growth. Humic substances in soil and crop sciences: Selected readings 161-186.

Cherr, C.M., J.M.S. Scholberg, and R. McSorley. 2006. Green manure as nitrogen source for sweet corn in a warm–temperate environment. Agronomy Journal 981173-1180.

Cline, G.R. and A.F. Silvernail. 2002. Effects of cover crops, nitrogen, and tillage on sweet corn. HortTechnology 12:118-125.

Crespo, P., J.G. Bordonaba, L.A. Terry, and C. Carlen. 2010. Characterisation of major taste and health-related compounds of four strawberry genotypes grown at different Swiss production sites. Food Chemistry 122:16-24.

Dabney, S.M., J.A. Delgado, and D.W. Reeves. 2001. Using winter cover crops to improve soil and water quality. Communications in Soil Science and Plant Analysis 32:1221-1250.

Decker, A.M., A.J. Clark, J.J. Meisinger, F.R. Mulford, and M.S. McIntosh. 1994. Legume cover crop contributions to no-tillage corn production. Agronomy Journal 86:126-135.

Dhima, K.V., I.B. Vasilakoglou, I.G. Eleftherohorinos, A.S. Lithourgidis. 2006. Allelopathic potential of winter cereals and their cover crop mulch effect on grass weed suppression and corn development. Crop Science 46:345-352.

Dimitri, C. and C. Greene. 2000. Recent growth patterns in the US organic foods market. Agriculture Information Bulletin, USDA Economic Research Service (ERS), Washington, D.C. <http://www.ers.usda.gov/media/249063/aib777_1_.pdf>. Accessed 22 Apr. 2016.

Divya, K., N.M. Roja, and S.B. Padal. 2015. Influence of seaweed liquid fertilizer of ulva lactuca on the seed germination, growth, productivity of Abelmoschus esculentus (L.). International Journal of Pharmacological Research 5:344-346.

Ebelhar, S.A., W.W. Frye, and R.L. Blevins. 1984. Nitrogen from legume cover crops for no-tillage corn. Agronomy Journal 76:51-55.

Fan, X.H. and Y.C. Li. 2010. Nitrogen release from slow-release fertilizers as affected by soil type and temperature. Soil Science Society of America Journal 74:1635-1641.

Farahi, M.H., A. Aboutalebi, S. Eshghi, M. Dastyaran, and F. Yosefi. 2013. Foliar application of humic acid on quantitative and qualitative characteristics of 'aromas' strawberry in soilless culture. Agricultural Communications 1:13-16.

98

FAWN (Florida Automated Weather Network). University of Florida. <http://fawn.ifas.ufl.edu>. Accessed 1 May 2016.

Fernandez-Salvador, J., B.C. Strik, and D.R. Bryla. 2015. Liquid corn and fish fertilizers are good options for fertigation in blackberry cultivars grown in an organic production system. HortScience 50:225-233.

Gagnon, B. and S. Berrouard. 1994. Effects of several organic fertilizers on growth of greenhouse tomato transplants. Canadian Journal of Plant Science 74:167-168.

Garland, B.C., M.S. Schroeder-Moreno, G.E. Fernandez, and N.G. Creamer. 2011. Influence of summer cover crops and mycorrhizal fungi on strawberry production in the southeastern United States. HortScience 46:985-991.

Gaskell, M. and R. Smith. 2007. Nitrogen sources for organic vegetable crops. HortTechnology 17:431–441.

Gharib, S.A., M.M. El-Mogy, A. Gawad, and E.A. Shalaby. 2011. Influence of compost, amino and humic acids on the growth, yield and chemical parameters of strawberries. Journal of Medicinal Plants Research 5:2304-2308.

Giampieri, F., J.M. Alvarez-Suarez, L. Mazzoni, S. Romandini, S. Bompadre, J. Diamanti, F. Capocasa, B. Mezzetti, J.L. Quiles, M.S. Ferreiro, and S. Tulipani. 2013. The potential impact of strawberry on human health. Natural Product Research 27:448-455.

Giampieri, F., S. Tulipani, J.M. Alvarez-Suarez, J.L. Quiles, B. Mezzetti, and M. Battino. 2012. The strawberry: composition, nutritional quality, and impact on human health. Nutrition 28:9-19.

Gliessman, S., M. Werner, S. Swezey, E. Caswell, J. Cochran, and F. Rosado-May. 1996. Conversion to organic strawberry management changes ecological processes. California Agriculture 50:24-31.

Guan, W., X. Zhao, D.J. Huber, and C.A. Sims. 2015. Instrumental and sensory analyses of quality attributes of grafted specialty melons. Journal of the Science of Food and Agriculture 95:2989-2995.

Guertal, E.A. and B.D. Green. 2012. Evaluation of organic fertilizer sources for south-eastern (USA) turfgrass maintenance. Acta Agriculturae Scandinavica 62:130-138.

Gündüz, K. and E. Özdemir. 2014. The effects of genotype and growing conditions on antioxidant capacity, phenolic compounds, organic acid and individual sugars of strawberry. Food Chemistry 155:298-303.

99

Haghighi, M., M. Kafi, and A. Khoshgoftarmanesh. 2013. Effect of humic acid application on cadmium accumulation by lettuce leaves. Journal of Plant Nutrition 36:1521-1532.

Hao, X.H., S.L. Liu, J.S. Wu, R.G. Hu, C.L. Tong, and Y.Y. Su. 2008. Effect of long-term application of inorganic fertilizer and organic amendments on soil organic matter and microbial biomass in three subtropical paddy soils. Nutrient Cycling in Agroecosystems 81:17-24.

Hargreaves, J.C., M. Adl, P.R. Warman, and H.P. Rupasinghe. 2008. The effects of organic and conventional nutrient amendments on strawberry cultivation: Fruit yield and quality. Journal of the Science of Food and Agriculture 88:2669-2675.

Hartwig, N.L. and H.U. Ammon. 2002. Cover crops and living mulches. Weed Science 50:688-699.

Havlin, J.L., D.E Kissel, L.D. Maddux, M.M. Claassen and J.H. Long. 1990. Crop rotation and tillage effects on soil organic carbon and nitrogen. Soil Science Society of America Journal 54:448-452.

Herencia, J.F., J.C. Ruiz-Porras, S. Melero, P.A. Garcia-Galavis, E. Morillo, and C. Maqueda. 2007. Comparison between organic and mineral fertilization for soil fertility levels, crop macronutrient concentrations, and yield. Agronomy Journal 99:973-983.

Hewett, E.W. 2006. An overview of preharvest factors influencing postharvest quality of horticultural products. International Journal of Postharvest Technology and Innovation 1:4-15.

Hoyt, G.D. and W.L. Hargrove. 1986. Legume cover crops for improving crop and soil management in the southern United States. HortScience 21:397-402.

Häkkinen, S.H. and A.R. Törrönen. 2000. Content of flavonols and selected phenolic acids in strawberries and Vaccinium species: influence of cultivar, cultivation site and technique. Food Research International 33:517-524.

Illera-Vives, M., S.S. Labandeira, L.M. Brito, A. López-Fabal, and M.E. López-Mosquera. 2015. Evaluation of compost from seaweed and fish waste as a fertilizer for horticultural use. Scientia Horticulturae 186:101-107.

Jeppsson, N. 2000. The effects of fertilizer rate on vegetative growth, yield and fruit quality, with special respect to pigments, in black chokeberry (Aronia melanocarpa) cv. Viking. Scientia Horticulturae 83:127-137.

Kader, A.A. 2008. Flavor quality of fruits and vegetables. Journal of the Science of Food and Agriculture 88:1863-1868.

100

Khan, W., U.P. Rayirath, S. Subramanian, M.N. Jithesh, P. Rayorath, D.M. Hodges, A.T. Critchley, J.S. Craigie, J. Norrie, and B. Prithiviraj. 2009. Seaweed extracts as biostimulants of plant growth and development. Journal of Plant Growth Regulation 28:386-399.

Khanizadeh, S., B. Ehsani-Moghaddam, and A. Levasseur. 2006. Antioxidant capacity in June-bearing and day-neutral strawberry. Canadian Journal of Plant Science 86:1387.

Koyuncu, M.A. and T. Dilmaçünal. 2010. Determination of vitamin C and organic acid changes in strawberry by HPLC during cold storage. Notulae Botanicae Horti Agrobotanici Cluj-Napoca 38:95.

Kuo, S. and E.J. Jellum. 2002. Influence of winter cover crop and residue management on soil nitrogen availability and corn. Agronomy Journal 94:501-508.

Lee, S.K. and A.A. Kader. 2000. Preharvest and postharvest factors influencing vitamin C content of horticultural crops. Postharvest Biology and Technology 20:207-220.

Li, Y., E.A. Hanlon, W. Klassen, Q. Wang, T. Olczyk, and I.V. Ezenwa. 2009. Cover crop benefits for South Florida commercial vegetable producers. IFAS. SL-242. <http://edis.ifas.ufl.edu/ss461/>. Accessed 15 June 2016.

Linares, J., J. Scholberg, K. Boote, C.A. Chase, J.J. Ferguson, and R. McSorley. 2008. Use of the cover crop weed index to evaluate weed suppression by cover crops in organic citrus orchards. HortScience 43:27-34.

Liu, M., F. Hu, X. Chen, Q. Huang, J. Jiao, B. Zhang, and H. Li. 2009. Organic amendments with reduced chemical fertilizer promote soil microbial development and nutrient availability in a subtropical paddy field: the influence of quantity, type and application time of organic amendments. Applied Soil Ecology 42:166-175.

Macdonald, A.J., P.R. Poulton, M.T. Howe, K.W.T. Goulding, and D.S. Powlson. 2005. The use of cover crops in cereal-based cropping systems to control nitrate leaching in SE England. Plant and Soil 273:355-373.

Mancuso S., E. Azzarello, S. Mugnai. X. Briand. 2006. Marine bioactive substances (IPA extract) improve ion fluxes and water stress tolerance in potted Vitis vinifera plants. Advances in Horticultural Science 20:156–161.

Miner, G.S., E.B. Poling, D.E. Carroll, L.A. Nelson, and C.R. Campbell. 1997. Influence of fall nitrogen and spring nitrogen—potassium applications on yield and fruit quality of ‘Chandler' strawberry. Journal of the American Society for Horticultural Science 122:290-295.

Mikkelsen, R. and T.K. Hartz. 2008. Nitrogen sources for organic crop production. Better Crops 92:16–19.

101

Miller, M.R., P.J. Dittmar, G.E. Vallad and J.A. Ferrell. 2014. Nutsedge (Cyperus spp.) control in bell pepper (Capsicum annuum) using fallow-period weed management and fumigation for two years. Weed Technology 28:653-659.

Mishra, R., and A. Kar. 2014. Effect of storage on the physicochemical and flavour attributes of two cultivars of strawberry cultivated in northern India. The Scientific World Journal 2014.

Mitchell, A.E., Y.J. Hong, E. Koh, D.M. Barrett, D.E. Bryant, R.F. Denison, and S. Kaffka. 2007. Ten-year comparison of the influence of organic and conventional crop management practices on the content of flavonoids in tomatoes. Journal of Agricultural and Food Chemistry 55:6154-6159.

Moreno, F., M. Monagas, G.P. Blanch, B. Bartolomé, and M.L.R. Del Castillo. 2010. Enhancement of anthocyanins and selected aroma compounds in strawberry fruits through methyl jasmonate vapor treatment. European Food Research and Technology 230:989-999.

Muramoto, J., S.R. Gliessman, D. Schmida, R. Stephens, C. Shennan, and S.T. Swezey. 2004. Nitrogen dynamics in an organic strawberry production system. Proceedings of California Organic Production and Farming in the New Millennium: A Research Symposium 131-134.

Mukkun, L., Z. Singh, D. Phillips. 2000. Nitrogen nutrition affects fruit firmness, quality and shelf life of strawberry. IV International Conference on Postharvest Science 553:69-71.

Muramoto, J., R.F. Smith, C. Shennan, K.M. Klonsky, J. Leap, M.S. Ruiz, and S.R. Gliessman. 2011. Nitrogen contribution of legume/cereal mixed cover crops and organic fertilizers to an organic broccoli crop. HortScience 46:1154-1162.

Möller, K., W. Stinner, and G. Leithold. 2008. Growth, composition, biological N2 fixation and nutrient uptake of a leguminous cover crop mixture and the effect of their removal on field nitrogen balances and nitrate leaching risk. Nutrient Cycling in Agroecosystems 82:233-249.

Nayak, D.R., Y.J. Babu, and T.K. Adhya. 2007. Long-term application of compost influences microbial biomass and enzyme activities in a tropical Aeric Endoaquept planted to rice under flooded condition. Soil Biology and Biochemistry 39:1897-1906.

Neri, D., E.M. Lodolini, G. Savini, P. Sabbatini, G. Bonanomi, F. Zucconi. 2002. Foliar application of humic acids on strawberry (cv Onda). Acta Horticulturae 594:297-302.

Neuweiler, R., L. Bertschinger, P. Stamp, B. Feil. 2003. The impact of ground cover management on soil nitrogen levels, parameters of vegetative crop development,

102

yield and fruit quality of strawberries. European Journal of Horticultural Science 84:183-191.

Newman, Y.C., D.L. Wright, C. Mackowiak, J.M.S. Scholberg, C.M. Cherr, and C.G. Chambliss. 2010. Cover crops. IFAS. SS-AGR-66. <http://edis.ifas.ufl.edu/aa217>. Accessed 3 May 2016.

Noling, J.W. 2015. Nematode management in strawberries. UF/IFAS Extension Publication ENY-031. <https://edis.ifas.ufl.edu/pdffiles/NG/NG03100.pdf>. Accessed 2 Apr. 2016.

Nunes, M.C. 2015. Correlations between subjective quality and physicochemical attributes of fresh fruits and vegetables. Postharvest Biology and Technology 107:43-54.

O’Connell, S., W. Shi, J.M. Grossman, G.D. Hoyt, K.L. Fager and N.G. Creamer. 2015. Short-term nitrogen mineralization from warm-season cover crops in organic farming systems. Plant and Soil 396:353-367.

Oberholtzer, L., C. Dimitri, and C. Greene. 2005. Price premiums hold on as US organic produce market expands. <http://www.ers.usda.gov/media/865206/vgs30801.pdf>. Accessed 15 June 2016.

Olsson, M.E., C.S. Andersson, S. Oredsson, R.H. Berglund, and K.E. Gustavsson, K.E. 2006. Antioxidant levels and inhibition of cancer cell proliferation in vitro by extracts from organically and conventionally cultivated strawberries. Journal of Agricultural and Food Chemistry 54:1248-1255.

Olsson, M.E., J. Ekvall, K.E. Gustavsson, J. Nilsson, D. Pillai, I. Sjöholm, U. Svensson, B. Åkesson, and M.G. Nyman. 2004. Antioxidants, low molecular weight carbohydrates, and total antioxidant capacity in strawberries (Fragaria× ananassa): effects of cultivar, ripening, and storage. Journal of Agricultural and Food Chemistry 52:2490-2498.

OMRI (Organic Materials Review Institute). <http://www.omri.org/>. Accessed 15 June 2016.

Orlova, O.V. and I.A. Arkhipchenko. 2009. Humic substances of composts from municipal solid wastes as a promising plant growth stimulator. Russian Agricultural Sciences 35:175-178.

Osborne, S.L. and W.E. Riedell. 2006. Starter nitrogen fertilizer impact on soybean yield and quality in the northern Great Plains. Agronomy Journal 98:1569-1574.

Ozores-Hampton, M. 2012. Developing a vegetable fertility program using organic amendments and inorganic fertilizers. HortTechnology 22:743-750.

103

Pang, X.P. and J. Letey. 2000. Organic farming challenge of timing nitrogen availability to crop nitrogen requirements. Soil Science Society of America Journal 64:247-253.

Papenfus, H.B., M.G. Kulkarni, W.A. Stirk, J.F. Finnie, J. Van Staden. 2013. Effect of a commercial seaweed extract (Kelpak®) and polyamines on nutrient-deprived (N, P and K) okra seedlings. Scientia Horticulturae Amsterdam 151:142–146.

Parr, M., J.M. Grossman, S.C. Reberg-Horton, C. Brinton, and C. Crozier. 2014. Roller-crimper termination for legume cover crops in North Carolina: Impacts on nutrient availability to a succeeding corn crop. Communications in Soil Science and Plant Analysis 45:1106-1119.

Pascual, I., I. Azcona, J. Aguirreolea, F. Morales, F.J. Corpas, J.M. Palma, R. Rellan-Alvarez, and M. Sanchez-Diaz. 2010. Growth, yield, and fruit quality of pepper plants amended with two sanitized sewage sludges. Journal of Agricultural and Food Chemistry 58:6951-6959.

Perez, A. and K. Plattner. 2013. Organic Fruit and Berries. <http://www.ers.usda.gov/media/1229855/fts-356sa.pdf>. Accessed 10 Mar. 2016.

Portz, D.N. and G.R. Nonnecke. 2011. Rotation with cover crops suppresses weeds and increases plant density and yield of strawberry. HortScience 46:1363-1366.

Quemada, M. and M.L. Cabrera. 1997. Temperature and moisture effects on C and N mineralization from surface applied clover residue. Plant and Soil 189:127-137.

Raese, J.T., S.R. Drake, and E.A. Curry. 2007. Nitrogen fertilizer influences fruit quality, soil nutrients and cover crops, leaf color and nitrogen content, biennial bearing and cold hardiness of ‘Golden Delicious’. Journal of Plant Nutrition 30:1585-1604.

Ranells, N.N. and M.G. Wagger. 1996. Nitrogen release from grass and legume cover crop monocultures and bicultures. Agronomy Journal 88:777-882.

Rathore, S.S., D.R. Chaudhary, G.N. Boricha, A. Ghosh, A., B.P. Bhatt, S.T. Zodape, and J.S. Patolia. 2009. Effect of seaweed extract on the growth, yield and nutrient uptake of soybean (Glycine max) under rainfed conditions. South African Journal of Botany 75:351-355.

Reganold, J.P., P.K. Andrews, J.R. Reeve, L. Carpenter-Boggs, C.W. Schadt, J.R. Alldredge, C.F. Ross, N.M. Davies, and J. Zhou. 2010. Fruit and soil quality of organic and conventional strawberry agroecosystems. Plos one 5:12346.

Reitz S.R., J.T. Trumble. 1996. Effects of cytokinin-containing seaweed extract on Phaseolus lunatus L.: influence of nutrient availability and apex removal. Botanica Marina 39:33-38.

104

Robertson, G.P. and P.M. Groffman. 2007. Nitrogen transformations. Soil Microbiology, Ecology, and Biochemistry 3:341-364.

Sainju, U.M., B.P. Singh, and S. Yaffa. 2002. Soil organic matter and tomato yield following tillage, cover cropping, and nitrogen fertilization. Agronomy Journal 94:594-602.

Salinas-Garcia, J.R., F.M. Hons, and J.E. Matocha. 1997. Long-term effects of tillage and fertilization on soil organic matter dynamics. Soil Science Society of America Journal 61:152-159.

Santos, B.M. 2010. Effects of preplant nitrogen and súlfur fertilizer sources on strawberry. HortTechnology 20:193-196.

Santos, B.M., N.A. Peres, J.F. Price, V.M. Whitaker, P.J. Dittmar, S.M. Olson and S.A. Smith. 2012. Strawberry Production in Florida. Vegetable Production Handbook. Gainesville, FL: University of Florida Institute of Food and Agricultural Sciences.

Santos, B.M. and M. Ramirez-Sanchez. 2009. Effects of preplant nitrogen fertilizer sources on strawberry. Proceedings of the Florida State Horticultural Society. 122:240-242.

Santos, B.M. and A.J. Whidden. 2007. Nitrogen fertilization of strawberry cultivars: Is preplant starter fertilizer needed? Univ. of Florida-IFAS. <http://edis.ifas.ufl.edu/pdffiles/HS/HS37000.pdf>. Accessed 16 Mar. 2016.

Sarrantonio, M. and E. Gallandt. 2003. The role of cover crops in North American cropping systems. Journal of Crop Production 8:53-74.

Schomberg, H.H., P.B. Ford, and W.L. Hargrove. 1994. Influence of crop residues on nutrient cycling and soil chemical properties. Managing Agricultural Residues. Lewis Publishers, Inc., Boca Raton, Florida, USA 99-122.

Schomberg, H.H., N.L. Martini, J.C. Diaz-Perez, S.C. Phatak, K.S. Balkcom, and H.L. Bhardwaj. 2007. Potential for using sunn hemp as a source of biomass and nitrogen for the Piedmont and Coastal Plain regions of the southeastern USA. Agronomy Journal 99:1448-1457.

Schulz, H. and B. Glaser. 2012. Effects of biochar compared to organic and inorganic fertilizers on soil quality and plant growth in a greenhouse experiment. Journal of Plant Nutrition and Soil Science 175:410-422.

Schwieterman, M.L., T.A. Colquhoun, E.A. Jaworski, L.M. Bartoshuk, J.L. Gilbert, D.M. Tieman, A.Z. Odabasi, H.R. Moskowitz, K.M. Folta, H.J. Klee, and C.A. Sims. 2014. Strawberry flavor: diverse chemical compositions, a seasonal influence, and effects on sensory perception. PLoS One 9:e88446.

105

Singh, R., R.R. Sharma, S. Kumar, R.K. Gupta, and R.T. Patil. 2008. Vermicompost substitution influences growth, physiological disorders, fruit yield and quality of strawberry (Fragaria x ananassa Duch.). Bioresource Technology 99:8507-8511.

Slinkard, K., and V.L. Singleton. 1977. Total phenol analysis: automation and comparison with manual methods. American Journal of Enology and Viticulture 28:49-55.

Smith, M.S., W.W. Frye, and J.J. Varco. 1987. Legume winter cover crops. Advances in Soil Science 95-139.

Soumare, M., F.M.G. Tack, and M.G. Verloo. 2003. Effects of a municipal solid waste compost and mineral fertilization on plant growth in two tropical agricultural soils of Mali. Bioresource technology 86:15-20.

Staley, L., D.G. Mortley, C.K. Bonsi, A. Bovell-Benjamin, and P. Gichuhi. 2013. Hydrolyzed organic fish fertilizer and poultry litter influence total phenolics and antioxidants content but not yield of amaranth, celosia, gboma, and long bean. HortScience 48:768-772.

Stewart, W., D. Dibb, A. Johnston, and T. Smyth. 2005. The contribution of commercial fertilizer nutrients to food production. Agronomy Journal 97:1-6.

Stivers-Young, L. 1998. Growth, nitrogen accumulation, and weed suppression by fall cover crops following early harvest of vegetables. HortScience 33:60-6.

Strik, B., T. Righetti, and G. Buller. 2004. Influence of rate, timing, and method of nitrogen fertilizer application on uptake and use of fertilizer nitrogen, growth, and yield of June-bearing strawberry. Journal of the American Society for Horticultural Science 129:165-174.

Teasdale, J.R. 1996. Contribution of cover crops to weed management in sustainable agricultural systems. Journal of Production Agriculture 9:475-479.

Terada, M., Y. Watanabe, M. Kunitomo, and E. Hayashi. 1978. Differential rapid analysis of ascorbic acid and ascorbic acid 2-sulfate by dinitrophenylhydrazine method. Analytical Biochemistry 84:604-608.

Thompson, G.D. and J. Kidwell. 1998. Explaining the choice of organic produce: cosmetic defects, prices, and consumer preferences. American Journal of Agricultural Economics 80:277-287.

Togun, A.O. and W.B. Akanbi. 2003. Comparative effectiveness of organic-based fertilizer to mineral fertilizer on tomato growth and fruit yield. Compost Science and Utilization 11:337-342.

106

Tonutare, T., U. Moor, and L. Szajdak. 2014. Strawberry anthocyanin determination by pH differential spectroscopic method–how to get true results? Acta Scientiarum Polonorum. Hortorum Cultus 13:35-47.

Touchton, J.T. and D.H. Rickerl. 1986. Soybean growth and yield responses to starter fertilizers. Soil Science Society of America Journal 50:234-237.

Tsao, R., D. Rekika, R. Yang, M.T. Charles, L. Gauthier, S. Khanizadeh, and A. Gosselin. 2007. Profile of antioxidant activities of selected strawberry genotypes. XII EUCARPIA Symposium on Fruit Breeding and Genetics 814:551-556.

Tulipani, S., G. Marzban, A. Herndl, M. Laimer, B. Mezzetti, and M. Battino. 2011. Influence of environmental and genetic factors on health-related compounds in strawberry. Food Chemistry 124:906-913.

Tulipani, S., B. Mezzetti, F. Capocasa, S. Bompadre, J. Beekwilder, C.R. De Vos, E. Capanoglu, A. Bovy, and M. Battino. 2008. Antioxidants, phenolic compounds, and nutritional quality of different strawberry genotypes. Journal of Agricultural and Food Chemistry 56:696-704.

USDA. 2015. Noncitrus Fruits and Nuts 2014 Preliminary Summary. 33. <http://www.usda.gov/nass/PUBS/TODAYRPT/ncit0115.pdf>. Accessed 1 May 2016.

USDA. 2010. Organic Production Survey (2008). 2010. 2007 Census of Agriculture. <https://www.agcensus.usda.gov/Publications/2007/Online_Highlights/Fact_Sheets/Practices/organics.pdf>. Accessed 2 Feb 2016.

USDA. 2016. Organic Survey (2014). 2016. 2012 Census of Agriculture. <https://www.agcensus.usda.gov/Publications/2012/Online_Resources/Organics/ORGANICS.pdf>. Accessed 1 May 2016.

USDA. 2013 b. USDA ERS-Organic Production. <http://www.ers.usda.gov/datafiles/Organic_Production/StateLevel_Tables_/Fruit.xls>. Accessed 12 Mar. 2016.

USDA. 2013 a. USDA ERS-Yearbook Tables. <http://www.ers.usda.gov/datafiles/Vegetable_and_Pulses_Yearbook_Tables/General/YRBK2016_Section%201_General.xlsx>. Accessed 12 Mar. 2016.

USDA National Agricultural Statistics Service. 2016. <https://quickstats.nass.usda.gov/>. Accessed 15 June 2016.

USDA Natural Resources Conservation Service. 2011. Carbon to Nitrogen Ratios in Cropping Systems. <http://www.nrcs.usda.gov/wps/PA_NRCSConsumption/download/?cid=nrcs142p2_052823&ext=pdf>. Accessed 1 May 2016.

107

Valdrighi, M.M., A. Pera, M. Agnolucci, S. Frassinetti, D. Lunardi, and G. Vallini. 1996. Effects of compost-derived humic acids on vegetable biomass production and microbial growth within a plant (Cichorium intybus)-soil system: a comparative study. Agriculture, Ecosystems and Environment 58:133-144.

Vetsch, J.A. and G.W. Randall. 2002. Corn production as affected by tillage system and starter fertilizer. Agronomy Journal 94:532-540.

Wang, S.Y., C.T. Chen, W. Sciarappa, C.Y. Wang, and M.J. Camp. 2008. Fruit quality, antioxidant capacity, and flavonoid content of organically and conventionally grown blueberries. Journal of Agricultural and Food Chemistry 56:5788-5794.

Wang, S.Y. and S.S. Lin. 2002. Composts as soil supplement enhanced plant growth and fruit quality of strawberry. Journal of Plant Nutrition 25:2243-2259.

Wang, S.Y., W. Zheng, and G.J. Galletta. 2002. Cultural system affects fruit quality and antioxidant capacity in strawberries. Journal of Agricultural and Food Chemistry 50:6534-6542.

Warner, J., T.Q. Zhang, X. Hao. 2004. Effects of nitrogen fertilization on fruit yield and quality of processing tomatoes. Canadian Journal of Plant Science 84:865-871.

Whitaker, V.M., C.K. Chandler, N. Peres, M.C. do Nascimento Nunes, A. Plotto, and C.A. Sims. 2015. Sensation™ ‘Florida127’Strawberry. HortScience 50:1088-1091.

Whitaker, V.M., C.K. Chandler, B.M. Santos, N. Peres, M.C. Nunes, A. Plotto, and C.A. Sims. 2012. Winterstar™ (‘FL 05-107’) strawberry. HortScience 47:296-298.

Whitaker, V.M., T. Hasing, C.K. Chandler, A. Plotto, and E. Baldwin. 2011. Historical trends in strawberry fruit quality revealed by a trial of University of Florida cultivars and advanced selections. HortScience 46:553-557.

Woods End® Laboratories. <https://woodsend.org/>. Accessed 15 June 2016.

Worthington, V. 2001. Nutritional quality of organic versus conventional fruits, vegetables, and grains. The Journal of Alternative and Complementary Medicine 7: 161-173.

Zheng, Y., C.Y. Wang, S.Y. Wang, and W. Zheng. 2005. Effect of superatmospheric oxygen on anthocyanins, phenolics and antioxidant activity of blueberries and strawberries. IX International Controlled Atmosphere Research Conference 857:475-482.

Zhong, W.H. and Z.C. Cai. 2007. Long-term effects of inorganic fertilizers on microbial biomass and community functional diversity in a paddy soil derived from quaternary red clay. Applied Soil Ecology 36:84-91.

108

Zodape, S.T., V.J. Kawarkhe, J.S. Patolia, and A.D. Warade. 2008. Effect of liquid seaweed fertilizer on yield and quality of okra (Abelmoschus esculentus L.). Journal of Scientific and Industrial Research 67:1115-1117.

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BIOGRAPHICAL SKETCH

Yurui was born and raised in Jiangsu, China. She received a Bachelor of Science

degree in Life Science and Technology from Nanjing Agricultural University (NJAU) in

2014. As an undergraduate student, she participated in a Student Research Training

project supported by NJAU on salt tolerance of inkberry (Ilex glabra L.) for a year.

During her senior year in 2013, she came to the University of Florida as an intern

and majored in Horticultural Sciences, through an internship program supported by the

China Scholarship Council.

In 2014, Yurui decided to pursue a master’s degree and was accepted into Gator

Nation in fall 2014 to work in Dr. Zhao’s lab.