Effects of biochar in combination with varied N inputs on grain yield, N uptake, NH volatilization, and NO emission in paddy soil.

Biochar application can improve crop yield, reduce ammonia (NH) volatilization and nitrous oxide (NO) emission from farmland. We here conducted a pot experiment to compare the effects of biochar application on rice yield, nitrogen (N) uptake, NH and NO losses in paddy soil with low, medium, and high N inputs at 160 kg/ha, 200 kg/ha and 240 kg/ha, respectively. The results showed that: (1) Biochar significantly increased the rice grain yield at medium (200 kg/ha) and high (240 kg/ha) N inputs by 56.4 and 70.5%, respectively. The way to increase yield was to increase the rice N uptake, rice panicle number per pot and 1,000 grain weight by 78.5-96.5%, 6-16% and 4.4-6.1%, respectively; (2) Under low (160 kg/ha) N input, adding biochar effectively reduced the NH volatilization by 31.6% in rice season. The decreases of pH value and NH-N content in surface water, and the increases of the abundance of NH-N oxidizing archaea and bacteria (AOA and AOB) communities contributed to the reduction of NH volatilization following the biochar application; (3) Under same N input levels, the total NO emission in rice season decreased by 43.3-73.9% after biochar addition. The decreases of K and S gene abundances but the increases of Z gene abundance are the main mechanisms for biochar application to reduce NO emissions. Based on the results of the current study, adding biochar at medium (200 kg/ha) N level (N200 + BC) is the best treatment to synchronically reduce NH and NO losses, improve grain yield, and reduce fertilizer application in rice production system.