Vermicompost extracts influence growth, total carotenoids, phenolics and antioxidant activity in Pak choi (Brassica rapa cv.

Bonsai, Chinensis group) grown under two fertilizer regimes Pant, A.1, T.J.K. Radovich1, N.V. Hue1, S.T. Talcott2, and K.A. Krenek2.

1Department of Tropical Plant and Soil Sciences, University of Hawai‘i, Honolulu, HI, USA 2Dept of Nutrition and Food Science, Texas A&M University, College Station, TX, USA

INTRODUCTION

Aqueous extracts of compost (compost tea), have been demonstrated to improve plant health, yield and nutritive quality when applied as a foliar spray or soil drench1.

Soluble mineral nutrients extracted from compost would have positive effect on plant growth.

It is also postulated that the action of microorganisms and microbial metabolites stimulate plant growth.

Multiple studies have reported on the effect of compost tea on suppression of certain plant diseases2,3,4,5.

Relatively little work has been done to investigate the effect of compost tea on yield and nutritional quality of vegetable crops.

Also, a lack of conclusive agreement on the effect of compost tea extraction methods on quality of compost tea stresses the need of this study.

OBJECTIVES

1) Determine the effects of extraction method on mineral nutrient content, chemical quality and biological activity of compost tea.

2) Evaluate the independent and interactive effects of compost tea type and fertilizer regime on plant yield, mineral nutrient concentration, phytonutrient content and antioxidant activity (ORAC).

Fig. 1. Treatment effects on plant growth under compost fertilization

MATERIALS AND METHODS

Two greenhouse full factorial experiments were arranged in completely randomized design for a total number of 8 treatments with 10 replications per treatment on Jan-Feb and April-May 2008.

Pak choi plants were grown under compost (chicken manure vermicompost) and chemical (Osmocote 16-16-16: N-P-K) fertilization at the rate of 135 kg N ha -1.

Compost teas were prepared with three different extraction methods: (i) non-aerated compost tea (NCT); (ii) aerated compost tea (ACT); and, (iii) aerated compost tea augmented with microbial enhancer (ACTME)6.

Compost teas and aerated water (control) were applied at the rate of 150 mL per pot weekly for four weeks starting 5 days after seed emergence to the root zone and foliage of plants.

Plants were harvested 5 weeks after emergence, and aboveground fresh and dry weight were recorded.

Chemical and microbial analysis of compost and compost tea were performed.

Mineral nutrients, phytonutrients, and antioxidant activities in plant tissue were analyzed.

RESULTS

Chemical and microbial properties of compost tea

Dissolved oxygen was lower and pH and mineral nutrients were higher in ACTME compared with the other teas. Total microbial population and activity did not differ with extraction method.

Treatment effect on plant growth, mineral nutrients and phytonutrients

All compost tea consistently increased above ground fresh and dry weight, total N P K per plant, and total carotenoids under both fertilizer regimes, however, the magnitude of the treatment effect was higher under compost compared to Osmocote (Fig 1 & 2).

Increase in yield and total carotenoids corresponded to N uptake under both fertilizer regimes (Fig. 3).

Fig. 2. Treatment effects on above ground fresh across fertilizer regime

Plant growth was positively associated with carotenoids and negatively associated with total phenolics and antioxidant activities (Fig 4 & Table 1).

The effect of compost tea extraction methods on fresh and dry weight, total N P K per plant and total carotenoids was not significantly different across fertilizer regimes.

Fig. 3. Above ground dry weight relative to N uptake across treatments

There was a significant interaction effect of compost tea and fertilizers on total phenolics.

The treatment effect on ORAC was not significant under Osmocote for all types of compost tea except NCT.

The effect of all compost tea on ORAC was lower than that of control under compost.

Fig. 4. Total phenolics relative to above ground dry weight across treatments

DISCUSSION AND CONCLUSIONS

All compost teas similarly enhanced plant production, mineral nutrient content and total carotenoids, and the effect was most prominent under organic fertilization.

The compost tea effect on crop attributes was attributed largely to a nutrient effect.

Antioxidant activity and total phenolics were higher under organic compared to synthetic fertilization.

Compost teas generally decreased phenolics under organic fertilization, and increased them slightly under synthetic fertilization.

Non significant differences among extraction methods on plant response within fertilizer regimes suggests that aeration and additives are not necessary for growth promotion and nutrient quality under the conditions reported here.

ACKNOWLEGDMENTSWe gratefully acknowledge the cooperation of Dr. Norman Arancon. This project has been funded by the USDA WSARE and TSTAR programs.

REFERENCES

1. Edwards CA, Arancon NQ and Greytak S, Effects of vermicompost teas on plant growth and disease. BioCycle 47:28-31 (2006).

2. Hoitink HAJ, Stone AG and Han DY, Suppression of plant diseases by composts. HortScience 32:184-187 (1997).

3. Scheuerell SJ and Mahaffee WF, Compost tea: Principles and prospects for plant disease control. Comp Sci Util 10:313-338 (2002).

4. Scheuerell SJ and Mahaffee WF, Variability associated with suppression of gray mold (Botrytis cinerea) on Geranium by foliar applicationsof non-aerated and aerated compost teas. Plant Disease 90:1201-1208 (2006).

5. Weltzien HC, Biocontrol of foliar fungal disease with compost extracts, in Microbial Ecology of Leaves, ed. by Andrews JH and Hirano SS. Springer-Verlag, New York, pp 430-450 (1991).

6. Ingham E, The Compost Tea Brewing Manual; Latest Methods and Research. Soil Food Web Inc., Corvallis, OR (2005).

Table 1. Effects of compost tea on total carotenoids, total phenolics and antioxidant activities (n = 20)

Compost

Extraction methodTotal Carotenoids

(mg kg -1)Total Phenolics

(mg kg -1)ORAC

(µmole TE g -1)

NCT 478.5 ± 35.3† 2313.4 ± 166.5 202.9 ± 18.8

ACTME 501.6 ± 38.6 2561.4 ± 209.0 178.4 ± 14.8

ACT 591.1 ± 46.7 2829.2 ± 231.5 240.2 ± 18.8

Control 305.2 ± 72.5 3398.0 ± 436.6 341.7 ± 118.4Osmocote

Extraction methodTotal Carotenoids

(mg kg -1)Total Phenolics

(mg kg -1)ORAC

(µmole TE g -1)

NCT 548.8 ± 45.7 2098.0 ± 97.6 171.2 ± 11.9

ACTME 517.3 ± 30.9 2363.6 ± 173.2 214.7 ± 18.7

ACT 566.9 ± 53.9 2433.8 ± 188.8 238.9 ± 16.0

Control 477.7 ± 38.2 1999.6 ± 147.3 223.3 ± 14.9

† Standard Error