What are some key agricultural sources of methane and nitrous oxide?

• A. Fossil fuel combustion for methane; fertilizer application for nitrous oxide.
• B. Soil erosion for methane; methane from rice paddies for nitrous oxide.
• C. Enteric fermentation in ruminant animals and rice paddies for methane; fertilizer application and manure management for nitrous oxide.
• D. Ocean upwelling for methane; plastic production for nitrous oxide.

Answer: (C)

The main idea is to connect specific farming activities to the two gases. Methane in agriculture mainly comes from enteric fermentation in ruminant animals (like cows, sheep, and goats) and from flooded rice paddies, where anaerobic conditions in the soil promote methanogenesis and methane release. Nitrous oxide from farming arises largely from nitrogen in soils after fertilizer application and from manure management, because soil and manure microbes convert nitrogen through nitrification and denitrification processes that release N2O. These pathways are well established as the principal agricultural sources for each gas: enteric fermentation and rice paddies for methane, fertilizer use and manure handling for nitrous oxide. Other options point to sources outside typical agricultural practices, such as fossil fuel burning or natural ocean processes, which are not the main agricultural contributors for these gases.