Which greenhouse gas is notably emitted from soil and manure management and fertilizer application, contributing to its potency?

• A. Methane
• B. Carbon dioxide
• C. Nitrogen gas
• D. Nitrous oxide

Answer: (D)

The main concept here is that nitrous oxide is released from soils when nitrogen is added through fertilizer and from manure management, due to microbial processes in the nitrogen cycle. When fertilizer is applied, soil microbes carry out nitrification (converting ammonium to nitrate) and denitrification (reducing nitrate to nitrogen gases). In these steps, nitrous oxide is produced and can escape into the atmosphere. It tends to be higher when soils are warm and moisture-rich or when there’s excess soil nitrogen. Nitrous oxide has a global warming potential about 300 times that of carbon dioxide over a century and lasts in the atmosphere for many decades, so even relatively small agricultural emissions can have a large warming impact. This combination of sources and high potency is what makes nitrous oxide the gas most notably linked to soil and fertilizer practices. In contrast, methane mainly comes from other agricultural pathways like enteric fermentation and anaerobic manure handling, and carbon dioxide comes from a wide range of sources, so they don’t specifically pinpoint this soil-fertilizer emission pattern. Nitrogen gas itself is not a greenhouse gas in this context.