Physico-chemical, microbial and phytotoxicity evaluation of composts from sorghum, finger millet and soybean straws

Purpose Composting is an environmentally sustainable alternative for bioconversion of agricultural residues into a nutrient-rich 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 (finger 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 efficient decomposition pattern of the agricultural residues characterized by high temperature profiles (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 final 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 significant GIs. It was difficult to attribute a single threshold GI value to indicate maturity of compost and could not further be applied to different types of composts as different seeds responded differently to the same compost

Physico-chemical, microbial and phytotoxicity evaluation of composts from sorghum, finger millet and soybean straws

Purpose Composting is an environmentally sustainable alternative for bioconversion of agricultural residues into a nutrient-rich 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 (finger 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 efficient decomposition pattern of the agricultural residues characterized by high temperature profiles (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 final 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 significant GIs. It was difficult to attribute a single threshold GI value to indicate maturity of compost and could not further be applied to different types of composts as different seeds responded differently to the same compost

Effect of macro- and micro-nutrients addition during anaerobic mono-digestion of grass silage in leach-bed reactors

The effect of macro- (NH4Cl) (set I) and micro-nutrients (Fe, Ni, Co and Mo) (set II) addition on chemical oxygen demand (COD) solubilisation during anaerobic mono-digestion of grass silage was investigated in two sets of leach bed reactor experiments at 35°C. Results showed that addition of NH4Cl and micro-nutrients improved COD solubilisation by 18% (0.56 g SCOD g−1 volatile solids) and 7% (0.45 g SCOD g−1 VS), respectively than control. About 20–50% of the added micro-nutrients were bioavailable in the produced leachates, while the rest (50–80%) were adsorbed onto the grass silage. Results of biological methane potential assays showed that, specific methane yields of grass silage were improved by 17% (0.36 ± 0.02 m3 CH4 kg−1 VSadded) when NH4Cl was supplemented while Fe, Ni, Co and Mo addition improved methane yields by 15% (0.33 ± 0.005 m3 CH4 kg−1 VSadded) when compared to control