mulching comparison for sweet potato production

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of 3 January 2013PRACTICAL FARMERS OF IOWAwww.practicalfarmers.org

Horticulture

About the Cooperators

Andy and Melissa Dunham own and oper-ate Grinnell Heritage Farm near Grinnell,Iowa. They grow USDA-certied organicvegetables, owers and herbs on their 80acre farm which has been in the fam-ily for over 150 years. They also tend asmall herd of beef cows raised on pasture.They market their produce through a CSA(Community Supported Agriculture), IowaCity Farmers Market, and through selectgrocery stores.

Scattergood Friends School is a smallQuaker boarding school about 15 mileseast of Iowa City, with approximately 10acres of IDALS-certied organic gardensand orchards and about 30 acres of pas-tures, upon which they grass-nish beef and lamb. Scattergood also raises heritagebreed Guinea hogs, a small ock of tur-keys, occasional broiler ocks, and a layingock of about 100 chickens. Scattergoodprimarily grows food for their school, butalso markets some products through New

Pioneer Coop in Iowa City and Coralville.

Background

Weed control is one of the primaryconcerns in vegetable production as itis labor-intensive and time-consuming.Mulches are often used to suppress weedgrowth as well as to prevent soil erosionand conserve soil moisture. While plasticmulch has been a standard mulch optionby many farmers, it raises waste disposalconcerns (Ingman et. al., 2012). The

purpose of this study was to investigatean effective and affordable alternativeto plastic mulch appropriate for sweetpotato production. To do so, cooperatorskept records of weed count, yield, andlabor involved for different types of mulchapplication as well as for the control plot(bare soil).

Methods

For this project, cooperators tested baresoil (control), common black plastic mulch,and paper mulch (WeedGuardPlus©)

in sweet potato production (Table 1).Because BioTELO©, a biodegradablemulch, is still in process of being approvedfor organic use in the United States (it hasbeen approved in Europe and Canada)and both cooperators’ farms are certiedorganic, we did not test BioTELO© thisyear.

At Grinnell Heritage Farm, plastic mulchwas laid with a raised-bed shaper, plastic

mulch layer. They tried to lay the papermulch with the same machine, but themulch ripped at the edges of raised beds,so rolled it out by hand and buried theedges.

At Scattergood Farm, beds were preparedwith a Maschio rototiller and dripirrigation lines were laid out. A mulchlayer was used for both the paper andthe plastic. Adjusting the irrigation hosesunder the paper caused many tears, sothey simply laid an additional soaker hose

Mulching Comparison for Sweet Potato Production

ork n together, a lwa s learn ng

Staff Contact:Tomoko Ogawa – (515) 232-5661

[email protected]

Cooperators:• Andy & Melissa Dunham – Grinnell

• Mark Quee – West Branch

Funding By:

CERES

Web Link:http://bit.ly/pf_horticulture

Research

Sweet potato mulch trial at Scattergood Friends School farm, West Branch, Iowa.

In a Nutshell

• Weed control is one of the primaryconcerns in vegetable production as it

is labor-intensive and time-consuming.• Cooperators tested bare soil, common

black plastic mulch, and paper mulch(WeedGuardPlus©) in sweet potatoproduction.

• Cooperators planted four replicationsof sweet potato rows.

• Both mulches resulted in fewer weeds.

• The plastic mulch resulted in thegreatest yields.

Project timeline:

May 2012 - September 2012




for the paper treatments. Next they pokedholes in the mulches and transplanted

the slips by hand. Cooperators plantedfour replications of sweet potato rows.Grinnell Heritage Farm planted thevariety ‘Beauregard’, and ScattergoodFriends School planted ‘Beauregard’ and‘Georgia Jet’. Plots were 100 feet long for‘Beauregard’ and 60 feet long for ‘GeorgiaJet’ at Scattergood Friends School.‘Beauregard’ plots were 40 feet long atGrinnell Heritage Farm. Each row wastreated with different mulch options or wasleft bare as the control. There was three tofour foot spacing between the rows. Plotswere replicated four times. Sweet potato

seedlings were planted with 12-inchspacing between plants.

Mulches were laid manually. After layingthe mulches, holes were manually punchedto transplant sweet potatoes by hand. Thetime required to apply different types of mulch was also recorded. Cooperator AndyDunham took a weed count once duringthe season by counting four randomlyselected one square foot quadrates withineach treatment. Cooperator Mark Queedid not take weed counts but alternativelyrecorded the hours spent weeding. He also

kept observation notes.

Cooperators harvested sweet potatoeswhen they reached peak maturity, andtook measurements for marketable yieldand the number of marketable versus culltubers. At Scattergood Farm, no edge rowswere planted, as they did not have enoughslips to ll the allocated space. ThereforeMark Quee and his students collecteddata on all of the rows. They dug eightcrowns from each row and weighed themindividually. Then they used a potato plowon the tractor to retrieve the rest of thesweet potatoes.

At Grinnell Heritage Farm, two differenttypes of mulches were applied on5/18/2012 followed by sweet potatoplanting on 5/21/2012. At ScattergoodFarm, the mulches were applied on5/23/2012 and they planted sweetpotatoes one week later on 5/30/2012.

Results

Labor Hours

At Scattergood Friends School, cooperator

Mark Quee reported that laying the

paper mulch required about two hours

more labor than the other treatments

due to complications with laying it down

and trying to work around the drip tape.

Beyond that, few differences in labor were

noted. Very little time was required for

weeding the mulched treatments but some

was required for the control treatment;

harvest times did not differ.

At Grinnell Heritage Farm, plastic mulchrequired the fewest hours overall (1.3 h),

followed by paper mulch (1.67 h) and bare

ground (1.82h). While bare ground did not

require installation or set-up time, more

time was spent weeding.

Weed Count

At Scattergood Farm, both mulch

treatments equally suppressed weed

growth. There were weeds present in

Descriptions of mulch products for the study

Product Description

Black plastic Black polyethylene plastic lm

WeedGuardPlus©Dark brown colored paper mulch. 100% biodegradable. Al-lows water, air and nutrients to permeate

Table 1

Average crown weight and yields between mulch

Mulch

‘Beauregard’ ‘Georgia Jet’

AverageCrown Weight

(lb)

Total RowYield (lb)

AverageCrown Weight

(lb)

Total RowYield (lb)

None (bare ground) 5.4 c 368.2 b 3.3 186.6

Paper 6.5 b 327.7 b 5.4 284.8

Plastic 8.5 a 522.4 a 10.1 354.2

Standard Error 0.57 42.13

P-value 0.0009 0.0634

Table 3

the bare ground control, but fewer than

normal due to the drought, according tocooperator Mark Quee.

At Grinnell Heritage Farm, weed counts

differed between the mulch types (P <

0.0001) and between the four replications

(P = 0.0037), as shown in Table 2. Bare

ground had the most weeds (89.9 per foot

of the bed), and like at Scattergood, the

mulches did not differ (7.3/ft for paper and

7.5/ft for plastic). Likely because of minor

soil gradients, there were more weeds

in the third rep than in other reps. Weed

counts in the bare soil varied between repsbut counts did not vary between reps in

either paper or plastic mulch

(mulch*rep P = 0.0149, data not shown).

Marketable Tubers and Yield

At Scattergood because of limited

replications within the ‘Georgia Jet’ variety,

results were unable to be included in

statistical analysis and are presented

as observations only. Eight randomly-

Marketable tubers, cull tubers, and weed cou

Mulch

MarketableTubers (#)

MarketableTubers (lb)

Cull Tubers(#)

Cull Tubers(lb)

WeedCount(per ft

None(bare ground)

41.8 38.5 b 0.5 b 0.5 c 89.9 a

Paper 39.8 38.3 b 1.5 ab 2.3 b 7.3 b

Plastic 41.5 42.3 a 2.0 a 3.8 a 7.5 b

Standard Error 2.47 0.49 0.37 0.45 3.85

P-value 0.8275 0.0020 0.0723 0.0064 < 0.000

Table 2

*means with different letters are statistically different

*means with different letters are statistically different




selected crowns (vines and all attached

tubers) were weighed within each replicate

of each treatment. Average crown weight

for the ‘Beauregard’ plants differed between

mulches (P = 0.0009) but not between reps

(P = 0.7733), as shown in Table 3. A similar

trend was noted in the ‘Georgia Jet’ crowns.

Total yield of sweet potatoes differed between

mulches in ‘Beauregard’ plants, being greatest

for plastic, and not differing between bare

ground and paper mulch (P = 0.0634).

Similarly, ‘Georgia Jet’ with plastic mulch

yielded the greatest numerically, but statistical

difference cannot be determined. No data

was available for cull tubers or pounds of cull

from Scattergood.

At Grinnell Heritage Farm, the mulch treatment

did not affect the number of marketable

tubers (P = 0.8275) but did affect the total

pounds of marketable sweet potatoes (P =

0.0020), as shown in Table 2. The plastic

mulch resulted in more marketable pounds

than did the bare ground or paper mulch

treatments, which did not differ. As with weedcount, there were rep differences in the total

marketable yield (P = 0.0032, data not shown),

probably due to within-eld variation. Where

weed pressure was the greatest within a

replicate the sweet potatoes yielded the least

and vice versa in the other replicates.

Conclusions and Next Steps

Data from the two farms indicate that mulchin either a plastic or paper form results infewer weeds during sweet potato growth,and the increased labor of laying the mulchmay be balanced out by the reduced weeding

labor. However, Mark Quee noted that themulches tended to blow around, leaving therows and sometimes damaging the plants.At both farms, the plastic mulch resultedin the greatest yields. At Grinnell HeritageFarm, however, it also resulted in more cullplants, though this may simply be due togreater production and not a greater percentof cull tubers. Paper mulch did not seem toimprove yields in the same way that plasticmulch did, but did reduce weeds equally aswell. More replications in future trials andexperimentation with additional mulch typesmay elucidate more differences.

Porter, D.O. WVU Extension Service. Are Mulches a Good Idea? <http://www.wvu.edu/~agexten/ageng/resource/mulch.htm>

Ingman, M., K. DiFrancesco, A. Doniger, T. Selko, D. Degeorge, I., Mil ler, and M. Anderson. 2012.Developing a Biodegradable Alternative to Plastic Mulch Film. Organic Broadcaster. Volume 20 • Number 3. Midwest Organic and Sustainable Education Service.

< http://www.mosesorganic.org/attachments/broadcaster/obonline203.pdf>

References PFI Cooperators’ ProgramPFI’s Cooperators’ Program givesfarmers practical answers to ques-tions they have about on-farmchallenges through research,record-keeping, and demonstrationprojects. The Cooperators’ Programbegan in 1987 with farmers lookingto save money through more judi-cious use of inputs.

Mulch May 2012

Mulch and sweet potatoes June 2012

Sweet potatoes July 2012

mulching comparison for sweet potato production

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