Biochemical properties of compost tea associated with compost quality and effects on pak choi growth

Abstract

This study investigated the links between variability in compost quality, the biochemical characteristics of their extracts (compost tea) and plant growth indicator through a series of experiments. Five different commercially produced composts were selected for quality evaluation. They were: (i) chicken manure-based thermophilic compost (ii) green waste thermophilic compost (iii) food waste vermicompost; (iv) chicken manure-based vermicompost (aged); and (v) chicken manure-based vermicompost (fresh). Compost teas were prepared from each compost using aerated extraction method with compost to water ratio of 1:10 (v:v), and were applied weekly for four weeks to pak choi (Brassica rapa cv Bonsai, Chinensis group) grown in a peat-perlite medium. The results demonstrated that compost quality generally impacted: (i) nutrient extraction efficiency (ii) microbial activity (iii) phytohormones and (iv) total nutrient content of the extracts. These differences in extract quality similarly impacted growth and mineral nutrient status of pak choi. Applications of compost tea increased growth and mineral nutrient content of pak choi. The responses were greater with aged chicken manure-based vermicompost tea, chicken manure-based thermophilic compost tea, and food waste vermicompost tea. The positive influence on plant growth was largely associated with mineral N and gibberellin (GA4) present in the teas. In vitro cultivation of pak choi with GA4 concentrations similar to those measured in the teas confirmed a direct positive effect of GA4 on growth. These findings suggest that either vermicompost or thermophilic compost can be used for the production of compost tea but the tea quality and its effect on plant may be predicted based on compost quality.