Wheat straw biochar reduces N2O emission by increasing denitrification in alkaline and acidic submerged paddy soils

Jun Shan1, Xu Zhao1, Shutan Ma1, Xiaoyuan Yan1

1 State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, China, Email: [email protected] or [email protected]

Abstract

Paddy fields are one of the most important N sinks in terrestrial ecosystems, and considerable N loss is caused by denitrification. Biochar has been recognized as useful soil amendment to paddy field in mitigating nitrous oxide (N2O) emission. However, the key mechanisms responsible for the reduced N2O emissions by biochar in paddy soils are still obscure. Here, using two paddy soils with contrasting pH, the denitrification and N2O emission were investigated in soil amened with different amounts of biochar (0%, 0.5% and 5%) via soil slurry incubation combined with N2/Ar technique. The results showed that biochar amendment significantly increased the pH values both in the alkaline and acidic soils. Biochar at 5% amendment rate significantly increased denitrification and significantly decreased N2O emission in soils. In the alkaline soil, biochar at 0.5% amendment rate significantly increased denitrification, but had no effect on N2O emission. Conversely, in the acidic soil, biochar at 0.5% amendment rate did not affect denitrification, but significantly reduced N2O emission. The N2O/(N2+N2O) ratio was significantly reduced by biochar amendment irrespective amendment rate both in alkaline and acidic soils. In the alkaline soil, biochar at 5% amendment rate significantly increased the abundance of nosZ genes, whereas biochar had no effect on the abundance of nosZ genes in the acidic soil irrespective of amendment rate. Our results suggested biochar effects in the alkaline soil were attributed to increase of denitrifying community, whereas biochar effects in the acidic soil was attributed to increase of pH.