Effects of fertilizer management practices on yield-scaled ammonia emissions from croplands in China: A meta-analysis

China is the world’s largest emitter of gaseous ammonia (NH 3 ), a compound carrying severe human health and ecosystem risks. Fertilizer N application is a major source of this atmospheric NH 3 . Although many studies have measured NH 3 emissions from croplands in China, the effect of fertilizer management on yield-scaled NH 3 emissions (i.e., NH 3 intensity defined as NH 3 emissions per unit crop yield) is not so clear. Thus, we performed a meta-analysis to quantify the effect of fertilizer management on NH 3 emissions and NH 3 intensity in China’s croplands. Results showed that the increases in NH 3 emissions and NH 3 intensity over a control were greater at high N rates (averaging 305 kg N ha −1 ) than at low and moderate N rates (average of 130 and 206 kg N ha −1 , respectively), while crop yields stayed flat over this range. Rice had greater increases in NH 3 emissions and NH 3 intensity in response to inorganic N addition than other crops. The emission factor for NH 3 was also higher for rice than other crops, and increased with increasing proportions of basal N and soil organic carbon and total N content. Relative to surface application, deep placement of fertilizer N significantly decreased NH 3 emissions and NH 3 intensity. Increasing the number of split applications of fertilizer N significantly reduced NH 3 emissions and NH 3 intensity. Organic manure amendments substituting for all or part of inorganic fertilizer N significantly mitigated NH 3 emissions and led to a reduction in NH 3 intensity but without statistical significance. The use of slow release fertilizers (SR) and urease inhibitors (UI) significantly reduced NH 3 emissions and NH 3 intensity, whereas application of nitrification inhibitors actually increased both. Overall, this meta-analysis demonstrates that appropriate fertilizer management practices such as reducing inorganic N rates, deep placement and split applications of fertilizer N, and using SR and UI can all reduce NH 3 emissions and NH 3 intensity in China’s croplands.