Synergistic and independent effects of crop residue and nitrogen fertilizer incorporation on nitrogen dynamics and GHG emissions

Crop residues with a high carbon-to-nitrogen (C/N) ratio immobilise nitrogen (N) released during decomposition in soil, thereby reducing nitrogen losses through leaching, denitrification and nitrous oxide (N2O) emissions. As microbial decomposition is mainly governed by C:N ratio, residues with wider C:N ratio promote nitrogen immobilisation, limit mineral N availability and slow down nitrification-denitrification pathways, ultimately influencing both CO2 and N2O fluxes. A laboratory incubation experiment was conducted over 120 days to investigate the influence of crop residues (paddy, maize, red gram, green gram and cotton) and mineral nitrogen additions on nitrogen immobilisation and greenhouse gas emissions. The experiment was laid out in a completely randomised design (CRD) with three replications and data were analysed using ANOVA to determine treatment differences. The experiment was performed under controlled conditions at room temperature with a moisture content of 55 % water-filled pore space. Residues were added at the rate of harvest biomass typically available to farmers in Telangana. Results indicated that maximum N2O emissions occurred within the first 30 days of incubation across all treatments. On average, incorporating residues into the soil increased N2O emissions by 66.78 % over control. Soil amended with residues exhibited significantly lower nitrate (NO3−–N) levels, with minimum values of 21 mg N kg-1 for maize and 27 mg N kg-1 for paddy observed on day 30. There was an increase in soil CO2 fluxes immediately following residue incorporation, with the highest CO2 emissions recorded in soil treated with cotton residue and nitrogen (19.95 µg C g-1 of soil). Cumulative CO2 emissions were highest in soil amended with green gram residue and inorganic nitrogen, which is attributed to the lower C:N ratio (21.81) of the residue, which enhanced the decomposition process and increased CO2 emissions. Cumulative N2O emissions were significantly higher when inorganic fertilizer nitrogen was applied along with residues, accounting for approximately 79.75 % more cumulative N2O emissions, compared to soil amended with residues alone.