Changes in fertilizer categories significantly altered the estimates of ammonia volatilizations induced from increased synthetic fertilizer application to Chinese rice fields

Abstract As the primary rice-producing country in the world, China has applied increasing amounts of synthetic fertilizers on rice fields, which has a large impact on environmental pollution and human health. In this study, a comprehensive inventory of fertilizer application to rice fields was compiled for China from 1979–2015. In 2015, fertilizer application was estimated to be 0.96 × 109 kg for early rice, 2.67 × 109 kg for single rice, and 1.11 × 109 kg for late rice. Based on the fertilizer application and region-specific emissions factors, ammonia (NH3) volatilizations from growing-season rice fields were estimated over the same period. We found that the total NH3 emissions increased during 1979–1998, while decreased during 1998–2015 with fluctuations. The decreasing trend of NH3 emission was likely attributed to changes of application proportions of ammonium bicarbonate (ABC) and other fertilizers. ABC and urea were the two dominant contributors, and contributed over 90% of the total NH3 emissions. Spatially, high emissions were identified in the Middle-lower Yangtze River Plain, Huaihe River Basin, Taihu Lake region, Pearl River delta and Sichuan basin. Monthly emissions patterns were estimated according to rice calendars. The damage from NH3 emissions was estimated as 26.79 billion yuan and accounted for 0.04% of the Gross Domestic Production of China in 2015. Finally, we discussed the NH3 reduction strategies from the perspective of both the government and farmers and suggested that an incentive scheme should be established to guide farmers to optimize traditional agricultural management.