Biochar as a tool to reduce environmental impacts of nitrogen loss in water-saving irrigation paddy field

Nitrogen (N) loss caused by excessive and incorrect application of N fertilizer in traditional rice-growing agriculture contributed to rural non-point source pollution and greenhouse gas emission, reduced crop N utilization efficiency. The objective of this study is to explore the response of N loss (leaching, NH3 volatilization and N2O emission) to different biochar applications (0,20,40 t/hm(2)) and irrigation patterns (controlled irrigation, flooding irrigation) in paddy fields of the Taihu Lake region (TLR) with the combination of field experiments and laboratory analysis. Based on the long-term observation of rice growth period, the ammonium N (NH4+-N), nitrate N (NO3--N) and total N (TN) leaching of paddy fields applied with water-saving irrigation (WSI) and biochar was measured in the plots of lysimeter. The impact of biochar application on NH3 volatilization, N2O emission in different water-carbon modes were clarified and the effect of water-carbon management modes on rice yield and yield components was analyzed. The results showed that the application of biochar reduced the NO3--N and TN leaching by 29.98% -38.63% and 12.77%-13.36%, increased rice seed setting rate and actual yield by 12.15%-15.28% and 1.67%-5.54%. Biochar addition inhibited NH3 volatilization and N2O emission. Under low-volume biochar (20 t/hm(2)), the main form of N leaching in rice fields was NO3--N, the NO3--N leaching accounted for 33.67% - 50.24% of the TN leaching; under high-volume biochar (40 t/hm(2)), N leaching in rice field was dominated by NH4+-N, the NH4+-N leaching accounted for 16.50% - 47.47% of the TN leaching. Controlled irrigation can not only reduce the water leakage in paddy fields but also reduce the N concentration in water leakage compared with flooding irrigation so that the total leaching of NH4+-N, NO3--N and TN in rice fields can be reduced by 23.44%, 47.89% and 50.69%. This study suggests that to make biochar beneficial for reducing environmental impacts of soil N effluxes and realizing cleaner production in rice cultivation, WSI technique and adapted use of biochar are of great importance. (C) 2021 Elsevier Ltd. All rights reserved.

Automated summary

This study investigated the response of nitrogen loss in paddy fields in the Taihu Lake region to different biochar applications and irrigation patterns. It found that biochar application can reduce nitrogen leaching and increase rice yield, while water-saving irrigation and proper use of biochar are crucial for reducing environmental impacts and achieving cleaner production in rice cultivation.