Forage conservation is a neglected nitrous oxide source

Agricultural activities are the major anthropogenic source of nitrous oxide (N 2 O), an important greenhouse gas and ozone-depleting substance. However, the role of forage conservation as a potential source of N 2 O has rarely been studied. We investigated N 2 O 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 N 2 O could be generated, which potentially places forage conservation as the third largest N 2 O source in the agricultural sector. Notably, the application of chlorate as an additive significantly reduced N 2 O production, but neither acetylene nor intermittent exposure to oxygen showed any impact. Overall, the results highlight that denitrifiers, rather than nitrifiers, are responsible for N 2 O production from silage, which was confirmed by molecular analyses. Our study reveals a previously unexplored source of N 2 O and provides a crucial mechanistic understanding for effective mitigation strategies. Significance Statement N 2 O is the third most important greenhouse gas (GHG) and agriculture contributes 80% of the total anthropogenic emissions in the US. The major sources of N 2 O 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 N 2 O, surpassing the field burning by 30. Our study provides a mechanistic understanding of N 2 O production and a simple and effective remedy for reducing N 2 O 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.