Effect of ammonium-based, non-sulfate fertilizers on CH4 emissions from a paddy field with a typical Chinese water management regime

The effects of ammonium-based, non-sulfate fertilizers, such as urea and/or ammonium phosphate (NH4H2PO4), on methane (CH4) emissions from paddy rice fields deserve attention, as they are being used increasingly for rice cultivation. A four-year field campaign was conducted in the Yangtze River Delta from 2004 to 2007 to assess the effects of different application rates of urea plus NH4H2PO4 on the CH4 emissions from a paddy rice field. The experimental field was under a typical Chinese water regime that follows a flooding-midseason drainage-reflooding-moist irrigation mode. Over the course of four years, the mean cumulative CH4 emissions during the rice seasons were 221, 136 and 112 kg C ha(-1) for nitrogen addition rates of 0, 150 and 250 kg N ha(-1), respectively. Compared to the treatment without nitrogen amendments, the 150 kg N ha(-1) decreased the CH4 emissions by 6-59% (P < 0.01 in one year, but not statistically significant in the others). When the addition rate was further increased to 250 kg N ha(-1), the CH4 emissions were significantly reduced by 35-53% (P < 0.01) compared to the no-nitrogen treatment. Thus, an addition rate of 250 kg N ha(-1), which has been commonly adopted in the delta region in the past two decades, can be regarded as an effective management measure as regards increasing rice yields while reducing CH4 emissions. Considering that doses of ammonium-based, non-sulfate fertilizers higher than 250 kg N ha(-1) currently are, and most likely will continue to be, commonly applied for paddy rice cultivation in the Yangtze River Delta and other parts of China, the inhibitory effects on CH4 emissions from rice production are expected to be pronounced at the regional scale. However, further studies are required to provide more concrete evidence about this issue. Moreover, further research is needed to determine whether N management measures are also effective in view of net greenhouse gas fluxes (including CH4, nitrous oxide, ammonia emissions, nitrate leaching and N loss from denitrification). (C) 2010 Elsevier Ltd. All rights reserved.