Open windrow composting of lignocellulosic crop residues and neem litter: Accounting for reactive nitrogen and greenhouse gas emissions

Abstract

Crop residue management plays a key role in reducing the environmental impact of agriculture, particularly through composting. Compost application to soil replenishes organic matter. A study was conducted to quantify the greenhouse gas emissions (GHG) (carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O)) and reactive nitrogen (Nr) losses (ammonia (NH3) and oxides of nitrogen (NOx)) from the open windrow composting of crop residues from three cereal crops (rice, maize and pearl millet) and neem litter. The windrow moisture was maintained between 50 and 60% with mechanical turning every 25 days. Compost maturity was reached after 137 days, indicated by a germination index (GI) > 80% and the ratio of initial to final C/N ratio, which was <0.4. CO2 and N2O emissions increased after turning, while CH4 emissions declined. The global warming potentials of the composts were 169.71, 184.13, 200.15, and 217.3 g CO2 eq. kg⁻1 initial dry matter (DM) for rice straw, maize stover, pearl millet stover, and neem litter, respectively. NH3 emissions ranged from 1.13 to 2.13 mg kg⁻1 initial DM, with neem litter producing more NH3 and less N2O due to its lower C/N ratio and nitrification inhibitory properties. Rice straw emitted the highest NOx (75.48 mg kg⁻1 DM), while maize stover had the lowest (28.39 mg kg⁻1 DM). Nitrogen losses from compost ranged from 8.16% in paddy straw to 0.53% in neem compost, with carbon losses ranging from 82.35% to 85.57%. The study concluded that careful management of moisture and aeration is critical for minimizing gaseous emissions from open windrow composting.