Meta-Analysis of Greenhouse Gas Emissions from Swine Manure Land Application

Swine operations are important sources of greenhouse gases, primarily methane (CH4) and nitrous oxide (N2O). The objective of the study was to provide a systematic review of the literature on GHG emissions from land following swine manure application through a meta-analysis that integrates results of individual previous studies. Results showed that, for CH4 emissions, land applied swine manure generate more emissions than land with no N added or land applied commercial N fertilizer. For N2O emissions, there was no significant difference between land applied with swine manure and that applied with commercial fertilizer of the same N amount. The CH4 and N2O emissions from swine manure land applications were commonly of the similar scale. Generally N2O emissions deserve more attention than CH4 emissions in swine manure land application, considering that the global warming potential of N2O is about 12 times higher than that of CH4 while CH4 and N2O emissions from swine manure land applications were commonly of the similar scale. The wide variations in reported N2O emission factors (0.7 to 2.2%, 95% CI in North American studies) indicate great potential in mitigating N2O emissions through optimized management practices. The N2O emissions from land applications can be affected by many factors, while factors affecting CH4 emissions were less studied. Results of meta-analysis indicated that CH4 emissions had an increasing trend with increasing annual average temperature and a deceasing trend with increasing annual precipitation.