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

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 (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.

Assessment of Physico-chemical, Microbial and Phytotoxic Changes of Various Organic Wastes During their Composting Process

“…For all the studied composts, there was an increase in electrical conductivity (EC) as the composting process progressed. These results confirmed those of Mupondi et al (2006) and Jagadabhi et al (2019). EC of all the compost materials increased from 5.51-8.27 mS/cm to 8.36-9.34 mS/cm after 170 days.…”

“…The increase in N content can be attributed to the loss of dry matter (as carbon) in the form of CO2 and water vapor loss during microbial decomposition and natural evaporation and processes. Several other studies reported similar results for N contents (Jagadabhi et al, 2019). However, the reduction of the N content could be due to the assimilation processes carried out by the utilization of inorganic nitrogen by microorganisms and the conversion of nitrogen into proteins, the mineralization and the volatilization (Cáceres et al, 2006;Pan and Sen, 2013).…”

Simulatenous evaluation of composting experiments and metagenome analyses to illuminate the effect of Streptomyces spp. on organic matter degradation

“…Hence the change of organic matter % was the rst set of measurements conducted during composting trials. The determination of germination index (GI %) was also adopted as a plant-based approach to evaluate the effect of degraded compost (Jagadabhi et al 2019;Pampuro et al 2017). GI % values were determined with 20 g samples diluted with 200 ml of de-ionized water for 5 h. The extract obtained after centrifugation at 10000 rpm was utilized with cucumber (Cucumis sativus) and wheat (Triticum) seeds.…”

Ecotoxicological Assessment of the Soilfertilized With Sewage Sludge

“…The GI values of all tested substrates reached values below 25%, which according to the scale developed by Wong, qualifies them as very phytotoxic (Wong et al, 2001). Phytotoxicity in the soil sewage extract typically results from the presence of partially degraded organic acids, fermentation intermediates, ammonia, salts and heavy metals (Jagadabhi et al, 2019).…”