Swine operations are important sources of greenhouse gases, primarily methane (CH_4) and nitrous oxide (N20). The objective of the study was to provide a systematic review of the literature on GHG emissions from land following swine manure applicationthrough a meta-analysis that integrates results of individual previous studies. Results showed that, for CH_4 emissions, land applied swine manure generate more emissions than land with no N added or land applied commercial N fertilizer. For N_2O emissions, there was no significant difference between land applied with swine manure and that applied with commercial fertilizer of the same N amount. The CH_4 and N_2O emissions from swine manure land applications were commonly of the similar scale. Generally N_2O emissions deserve more attention than CH_4 emissions in swine manure land application, considering that the global warming potential of N_2O is about 12 times higher than that of CH_4 while CH_4 and N_2O emissions from swine manure land applications were commonly of the similar scale. The wide variations in reported N_2O emission factors (0.7 to 2.2%, 95% CI in North American studies) indicate great potential in mitigating N_2O emissions through optimized management practices. The N_2O emissionsfrom land applications can be affected by many factors, while factors affecting CH_4 emissions were less studied. Results of meta-analysis indicated that CH_4 emissions had an increasing trend with increasing annual average temperature and a deceasing trend with increasing annual precipitation.
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