Can biochar amendment be an ecological engineering technology to depress N2O emission in rice paddies?-A cross site field experiment from South China

Approaches to reduce N2O emission from crop ecosystems deserves urgent need for climate change mitigation in world agriculture. Yet, unique ecological measures to depress N emission while conserving crop productivity have not yet been well developed for wide ranges of crop ecosystems. In order to establish an ecological engineering option to mitigate N2O emission in rice ecosystems, we conducted a field experiment with biochar amendment on N2O emission from rice paddies in three sites across South China in 2010. This experiment was performed with 6 treatments of biochar rates of O. 20. and 40 t ha(-1) with and without N fertilization respectively. The rice ecosystem was managed with conventional crop production practices as seasonally man-managed wetlands, which were under flooding after seedling transplantation till panicling and drainage during spiking followed by a subsequent moist condition (F-D-M) till harvest across sites. Emission of N2O from rice soil was monitored with closed chambers at 7 days interval throughout the whole rice growing season (WRGS) and the gas samples analyzed with a gas chromatograph (Agilent 7890D) equipped with an electron capture detector (ECD). Total emission of N2O-N ranged from 1.5 kg N2O-N ha(-1) to 1.9 kg N2O-N ha(-1) without biochar, and from 0.8 kg N2O-N ha(-1) to 1.3 kg N2O-N ha(-1) and from 0.7 kg N2O-N ha(-1) to 0.9 kg N2O-N ha(-1) with biochar amendment at 20 t ha(-1) and 40 t ha(-1), respectively. Thus, biochar amendment depressed total N2O emission from chemical N fertilizer, as the calculated EF of N2O-N emission was reduced from 0.57 +/- 0.15% under chemical N fertilizer only to 0.36 +/- 0.08% and 0.22 +/- 0.04% under biochar amendment at 20 t ha(-1) and 40 t ha(-1) respectively. The value under biochar amendment at 40 t ha(-1) was found even much smaller than that of a continuously flooding rice ecosystem. As soil pH (H2O), content of soil organic carbon and total N were all upraised significantly, biochar amendment improved rice ecosystem functioning by decreasing N2O-N emission per metric ton of rice production from 0.17 +/- 0.02 kg N2O-N without biochar to 0.10 +/- 0.02 and 0.07 +/- 0.03 kg N2O-N under biochar respectively at 20 t ha(-1) and 40 t ha(-1). Thus, soil amendment of biochar from crop straw could be adopted as a unique ecological engineering measure to reduce N2O emission while enhancing soil fertility and sustaining rice productivity in rice ecosystems. (C) 2012 Elsevier B.V. All rights reserved.