Simultaneous effects of biochar and nitrogen fertilization on nitrous oxide and methane emissions from paddy rice.

Synthetic fertilizers are major agents of gaseous emissions including nitrous oxide (NO), and rice cultivation is a primary source of methane (CH) emission. Biochar (BC) addition to agricultural soils is a potential approach to mitigate NO and CH emissions. This greenhouse study was conducted to assess the simultaneous effects of BC and nitrogen (N) fertilization to reduce NO and CH emissions along with higher biomass accumulation in rice under controlled conditions. Nine treatment combinations of BC amendments at 0, 2 and 4% by weight (weight of BC/weight of soil) mixed into 3500 g of unsterile soil with 0, 70 and 140 kg N ha were used in growing rice. Results show that BC-only treatments enhanced the volumetric water contents (VWC) by 9-14% and soil pH by 5-7% coupled with higher daily and cumulative seasonal CH-C fluxes by 85-95% and 48-51%, respectively, compared with control treatment. Under 2% and 4% BC amendments, N at 140 kg ha lowered the daily and cumulative seasonal CH-C fluxes by 24-42% and 20-30%, respectively as compared to 70 kg N ha. Furthermore, BC amendments in N-treated soils reduced the daily and total seasonal NO-N emissions by 27-67% and 49-61%, respectively, relative to N-only treatments. However, N addition in BC-amended soils showed 10-16% decreased VWC compared with the BC-only treated soils. In terms of rice growth, BC-only reduced the above- and below-ground biomass accumulation, delayed the tillering phase, and resulted in fewer vegetative tillers except for BC-treated pots with 140 kg N ha. Thus, this study suggests that the use of BC amendment at 2% with 140 kg N ha may be a beneficial strategy to reduce the net GHG emissions from paddy rice in an Alfisol.