Pak Choi (Brassica rapa, Chinensis Group) Yield, Phytonutrient Content, and Soil Biological Properties as Affected by Vermicompost-to-water Ratio Used for Extraction

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: I) 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.