Comparative Effectiveness of Organic Substitution in Fertilizer Schedule: Impacts on Nitrous Oxide Emission, Photosynthesis, and Crop Productivity in a Tropical Summer Rice Paddy

Studies on replacement of inorganic fertilizer with organic residues to improve crop productivity and their impact on greenhouse gas emission from agricultural soil merit more attention. Two-year field experiments were conducted to study the impact of different organic residues with varied carbon (C)/nitrogen (N) ratios as substitutes of chemical fertilizer on emission reduction of nitrous oxide (N2O) and crop yield from a tropical summer rice paddy of India. Five treatments comprising of conventional N fertilizer (NPK), cow manure (CD), rice straw (RS), poultry manure (PM), and sugarcane bagasse (SCB) were applied in a rice field to estimate N2O emission. Application of CD (at 10 t ha(-1)) resulted in maximum reduction of seasonal N2O emissions (15 %) over NPK, RS, PM, and SCB. Application of CD and RS enhanced leaf photosynthetic rate and caused maximum utilization of photosynthates towards developing grains as evident from grain filling ability and higher grain yield. Substitution of NPK with organic residues enhanced soil nutrient availability in terms of C and N resulting in improved soil fertility and to some extent influenced soil nitrogen processes which in turn reduced N2O emissions. We conclude that suitable management of soil in agricultural ecosystem can reduce the emission of N2O and protect and preserve the soil health without compromising the agronomic productivity reducing the use of chemical fertilizer and maintaining the sustainability of rice ecosystem as evident from lower carbon equivalent emissions (CEE) and higher carbon efficiency ratio (CER) at CD in rice paddies in the present study.