Forage conservation is a neglected source of nitrous oxide

Abstract

Agricultural activities are the major anthropogenic source of nitrous oxide (N2O), an important greenhouse gas and ozone-depleting substance. However, the role of forage conservation as a potential source of N2O has rarely been studied. We investigated N2O production from the simulated silage of the three major crops--maize, alfalfa, and sorghum--used for silage in the US, which comprises over 90% of the total silage production. Our findings revealed a substantial N2O could be generated, which potentially places forage conservation as the third largest N2O source in the agricultural sector. Notably, the application of chlorate as an additive significantly reduced N2O production, but neither acetylene nor intermittent exposure to oxygen showed any impact. Overall, the results highlight that denitrifiers, rather than nitrifiers, are responsible for N2O production from silage, which was confirmed by molecular analyses. Our study reveals a previously unexplored source of N2O and provides a crucial mechanistic understanding for effective mitigation strategies. Significance StatementN2O is the third most important greenhouse gas (GHG) and agriculture contributes 80% of the total anthropogenic emissions in the US. The major sources of N2O in the agricultural sector identified by the USEPA include agricultural land management, manure management, and the field burning of agricultural residues. Here, we show that forage conservation could be a significant unaccounted source of N2O, surpassing the field burning by 30. Our study provides a mechanistic understanding of N2O production and a simple and effective remedy for reducing N2O emissions. The findings have substantial implications for mitigating climate change, informing policy-makers, and guiding future research on reducing greenhouse gas emissions from livestock production.