Effect of nitrogen application rate under organic and conventional systems on rice (Oryza sativa L.) growth, grain yield, soil properties, and greenhouse gas emissions

Abstract

The use of appropriate nitrogen (N) rates is important to optimize organic rice yield potential while minimizing environmental impact and input costs. A greenhouse experiment was conducted to identify the optimal N rate for organic and conventional rice and determine its effects on rice yield, soil properties, and greenhouse gas emissions. Six N rates (0, 50, 100, 150, 200, and 250 kg ha−1) and two cropping systems (organic, conventional) were included in this study. Plant dry biomass, panicle number, and yield of conventional rice linearly increased with increasing N rate from 0 to 250 kg ha−1, whereas those of organic rice increased significantly with increasing N rate until 200 kg ha−1. Conventional rice had a significantly taller plant, whereas organic rice had a significantly greater tiller number. At the optimal N rate, the panicle number and yield of organic rice were 77.3% and 92.7% of those of conventional rice, respectively. CO2 and CH4 emissions peaked at the reproductive stage, whereas N2O emissions peaked at the vegetative stage. Global warming potential (GWP) increased with increasing N rate and peaked at 200 and 250 kg N ha−1, respectively, in the organic and conventional system; however, greenhouse gas intensity (GHGI) was not affected by N rate in both systems. Of the measured soil parameters, total microbial biomass (TMB) was significantly correlated to plant growth, yield, and GWP. Our study indicated that the optimal N rate was 200 kg ha−1 for organic rice and 250 kg ha−1 or higher for conventional rice to approach yield potential.