The 2012 ASHS Annual Conference

This study investigated the links between variability in compost quality, the biochemical characteristics of their extracts (compost tea) and plant growth indicators through a series of experiments. Five composts that varied widely in feedstock and production methods were selected for quality evaluation. They were: (i) chicken manure-based thermophilic compost (ii) green waste thermophilic compost (iii) food waste vermicompost; (iv) aged chicken manure-based vermicompost; and (v) fresh chicken manure-based vermicompost. 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. 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 different GA₄ concentrations (0–3200 ng·L^-1) 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.