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  • Author or Editor: Archana Pant x
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Previous work has demonstrated the potential of compost tea to enhance plant growth and nutritional status. One factor thought to contribute to variability in the efficacy of compost tea is the amount of compost per unit volume of water. To address these gaps in our understanding, two greenhouse trials and two field trials were conducted to investigate the effects of various extraction ratios on the growth, mineral nitrogen (N), and phytonutrient content of pak choi (Brassica rapa, Chinensis) and on soil biological properties. In greenhouse experiments, plants were fertilized with a single rate of chicken manure-based thermophilic compost. In field trials, three fertilizer treatments: 1) rendered meat byproduct or Tankage (Island Commodities, Honolulu, HI); 2) soluble fertilizer (16:16:16); and 3) chicken manure-based thermophilic compost were applied. Aerated vermicompost teas were prepared using chicken manure-based vermicompost and water at various ratios. Pak choi plants were treated weekly for 4 weeks with 10%, 5%, 3%, and 1% vermicompost teas in the greenhouse experiments and 10% and 5% teas in the field trials. Applications of vermicompost tea significantly increased plant growth, N content, total carotenoids, and total glucosinolates in plant tissue; this response was greatest in chicken manure-fertilized treatments. Increases in yield and phytonutrient content were associated with increased N uptake. Vermicompost tea also increased soil respiration and dehydrogenase activity over the control (water). Plant growth, phytonutrient content, and microbial activities in soil increased with increasing concentrations of vermicompost tea. Within the range of concentrations evaluated (1%–10%), greatest plant growth response was observed with 5% and 10% vermicompost tea, indicating that the optimal water-to-vermicompost ratio for extraction is lower than 50:1 and is likely in the range of 10:1 to 20:1. The findings suggest that vermicompost tea could be used to improve plant nutrient status and enhance soil biological properties in vegetable production.

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Greenhouse experiments were conducted to evaluate the effects of different concentrations of vermicompost water extracts (teas) and seed soaking duration on germination of tomato (Solanum lycopersicum) and lettuce (Lactuca sativa) seeds. In the first experiment, tomato and lettuce seeds were soaked in vermicompost teas prepared from chicken manure-based vermicomposts for 9 hours. The concentrations of the extracts used were 10%, 5%, 3%, 1% (1:10, 1:20, 1:33, and 1:100 vermicompost-to-water ratio by volume), and 0% (water control). Seeds were sown in peat–perlite medium, and seedlings were harvested after 4 weeks. Soaking seeds in vermicompost teas significantly (P < 0.0001) increased germination percentage and seedling growth of tomato and lettuce compared with control. The response to concentrations of the vermicompost tea was generally linear. In another experiment, tea produced from food waste-based vermicompost was used. Tomato seeds were soaked in 20%, 10%, 5%, 1%, and 0% teas after 24 hours of soaking and sown into a sphagnum moss-based medium. Plant responses were linear and quadratic for germination and growth, respectively, with 1% vermicompost tea increasing germination, whereas 5% vermicompost tea significantly promoted growth. A third experiment was done to evaluate the interaction of a range of vermicompost tea concentrations (20%, 10%, 5%, 1%, and 0%) and length of soaking (24, 12, 8, 4, 1 hours, and 0: no soaking) on the germination of tomato seeds. There was a significant interaction (P < 0.001) between the concentration of vermicompost teas and lengths of soaking. Soaking duration generally had a significantly positive and linear effect on germination of tomato seeds across the concentrations of vermicompost tea. Germination rates of tomato seeds were significantly greater after 8, 12, and 24 hours of soaking. However, within each soaking duration, concentrations of vermicompost teas had variable effects on seed germination. The presence of N-indole-3-acetic acid (IAA), cytokinin, gibberellins, and humic acids in the teas could have been responsible for the faster germination of tomato seeds when soaked at lower concentrations and longer soaking times.

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Reducing grower reliance on off-island inputs to promote plant nutrition was identified by industry as a high priority in efforts to improve agricultural sustainability in Hawai’i. A variety of knowledge gaps exist that prevent producers from using locally produced amendments in the fertility program. This study will focus on recent transdisciplinary efforts at the University of Hawai’i to improve understanding of factors that affect variability in the quality, application, efficacy, and cost-effectiveness of locally produced composts, vermicomposts, rendered animal products, and algae in Hawai’i. A series of greenhouse, experiment station, and on-farm trials have supported several conclusions, including 1) aqueous extracts of vermicomposts and high-quality, farmer-produced thermophilic composts can effectively improve crop growth and reduce costs associated with the use of these inputs; 2) replacement of peat and other imports with local materials in vegetable seedling production have the potential to improve seedling vigor and reduce costs in the long term; 3) commercially produced rendered meat products, alone and in combination with commercial composts, are a valuable local source of nitrogen (N); and 4) invasive algae from coral reef remediation may provide a significant source of potassium (K) in the near term, but K content of algae is highly dependent on species and location of growth.

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