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
Treatment effect on plant growth, mineral nutrients and phytonutrients
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.
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).
Soluble mineral nutrients extracted from compost would have positive effect on
plant growth.
Increase in yield and total carotenoids corresponded to N uptake under both
fertilizer regimes (Fig. 3).
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.
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. 2. Treatment effects on above ground fresh across fertilizer regime
Fig. 4. Total phenolics relative to above ground dry weight across treatments
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.
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.
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.
ACKNOWLEGDMENTS
We gratefully acknowledge the cooperation of Dr. Norman Arancon. This project
has been funded by the USDA WSARE and TSTAR programs.
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) nonaerated compost tea (NCT); (ii) aerated compost tea (ACT); and, (iii) aerated
compost tea augmented with microbial enhancer (ACTME)6.
Fig. 3. Above ground dry weight relative to N uptake across treatments
Table 1. Effects of compost tea on total carotenoids, total phenolics and
antioxidant activities (n = 20)
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.
Compost
Plants were harvested 5 weeks after emergence, and aboveground fresh and
dry weight were recorded.
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
Osmocote
305.2 ± 72.5
3398.0 ± 436.6
341.7 ± 118.4
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.
Extraction method
Extraction method
Total Carotenoids
(mg kg -1)
Total Carotenoids
(mg kg -1)
Total Phenolics
(mg kg -1)
Total Phenolics
(mg kg -1)
ORAC
(µmole TE g -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
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