Physico‑chemical, microbial and phytotoxicity evaluation of composts from sorghum, fnger millet and soybean straws

Authors

1 International Crops Research Institute for the Semi-Arid Tropics (ICRISAT)

2 International Institute of Tropical Agriculture (IITA)

Abstract

Purpose Composting is an environmentally sustainable alternative for bioconversion of agricultural residues into a nutrientrich product that can enhance soil fertility/microbial diversity and thereby improve agricultural productivity. The goal of the current study was to evaluate the decomposition pattern of the agro-residues and assess the maturity and phytotoxicity of the composts obtained using physico-chemical, microbial and statistical analyses. The study also attempted to determine a threshold germination index (GI) to serve as a maturity index for the composts by conducting seed germination assays with tomato, chickpea and soybean seeds. Methods Three agricultural residues/straws of Eleusine coracana (fnger millet), Sorghum bicolor (sorghum) and Glycine max (soybean) were subjected to aerobic composting for a period of 60 days to study the impact of saw dust on the decomposition pattern and the ultimate compost quality/characteristics. Results The results showed efcient decomposition pattern of the agricultural residues characterized by high temperature profles (up to 70 °C), high microbial activity, a sharp decrease in C/N ratio of the composting materials, i.e., from an initial 41–61 to fnal 10–17. Conclusions Statistical evaluation of seed germination assays showed that only the compost obtained from sorghum straw+saw dust was mature and free from any phytotoxicity as all the tested seeds showed higher and statistically signifcant GIs. It was difcult to attribute a single threshold GI value to indicate maturity of compost and could not further be applied to diferent types of composts as diferent seeds responded diferently to the same compost.

Keywords