Forage conservation is a neglected nitrous oxide source

Agricultural activities are the major anthropogenic source of nitrous oxide ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub><mml:mstyle><mml:mtext>N</mml:mtext></mml:mstyle> <mml:mn>2</mml:mn></mml:msub> <mml:mstyle><mml:mtext>O</mml:mtext></mml:mstyle> </mml:math> ), an important greenhouse gas and ozone-depleting substance. However, the role of forage conservation as a potential source of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub><mml:mstyle><mml:mtext>N</mml:mtext></mml:mstyle> <mml:mn>2</mml:mn></mml:msub> <mml:mstyle><mml:mtext>O</mml:mtext></mml:mstyle> </mml:math> has rarely been studied. We investigated <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub><mml:mstyle><mml:mtext>N</mml:mtext></mml:mstyle> <mml:mn>2</mml:mn></mml:msub> <mml:mstyle><mml:mtext>O</mml:mtext></mml:mstyle> </mml:math> production from the simulated silage of the three major crops-maize, alfalfa, and sorghum-used for silage in the United States, which comprises over 90% of the total silage production. Our findings revealed that a substantial <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub><mml:mstyle><mml:mtext>N</mml:mtext></mml:mstyle> <mml:mn>2</mml:mn></mml:msub> <mml:mstyle><mml:mtext>O</mml:mtext></mml:mstyle> </mml:math> could be generated, potentially placing forage conservation as the third largest <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub><mml:mstyle><mml:mtext>N</mml:mtext></mml:mstyle> <mml:mn>2</mml:mn></mml:msub> <mml:mstyle><mml:mtext>O</mml:mtext></mml:mstyle> </mml:math> source in the agricultural sector. Notably, the application of chlorate as an additive significantly reduced <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub><mml:mstyle><mml:mtext>N</mml:mtext></mml:mstyle> <mml:mn>2</mml:mn></mml:msub> <mml:mstyle><mml:mtext>O</mml:mtext></mml:mstyle> </mml:math> production, but neither acetylene nor intermittent exposure to oxygen showed any impact. Overall, the results highlight that denitrifiers, rather than nitrifiers, are responsible for <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub><mml:mstyle><mml:mtext>N</mml:mtext></mml:mstyle> <mml:mn>2</mml:mn></mml:msub> <mml:mstyle><mml:mtext>O</mml:mtext></mml:mstyle> </mml:math> production from silage, which was confirmed by molecular analyses. Our study reveals a previously unexplored source of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub><mml:mstyle><mml:mtext>N</mml:mtext></mml:mstyle> <mml:mn>2</mml:mn></mml:msub> <mml:mstyle><mml:mtext>O</mml:mtext></mml:mstyle> </mml:math> and provides a crucial mechanistic understanding for effective mitigation strategies.