Soil Type Determines Whether Added Carbon and Nitrogen Curb or Intensify Nitrous Oxide Emissions

Agricultural soils are a major source of nitrous oxide, a powerful greenhouse gas produced largely through microbial nitrogen transformations. A new study comparing five representative Chinese farmland soils reveals that the same carbon and nitrogen inputs can produce sharply different emission outcomes depending on soil acidity, nutrient conditions, and microbial function.

Researchers examined black soil, lime concretion black soil, yellow-cinnamon soil, red soil, and fluvo-aquic soil collected from agricultural regions across China. The soils represented contrasting physicochemical properties and histories of low or high fertilizer application.

The team combined bacterial community sequencing, measurements of key denitrification genes, and controlled laboratory incubations that continuously monitored nitrous oxide and nitrogen gas production. Their results showed that soil pH and nitrate availability were the strongest factors shaping bacterial community structure, with pH alone explaining nearly half of the observed variation.

“Our findings show that agricultural soils cannot be treated as if they respond uniformly to fertilizer and carbon inputs,” said corresponding author Xiaojun Zhang. “The local soil environment determines how microbial communities process nitrogen and whether denitrification ends with nitrous oxide or proceeds to harmless nitrogen gas.”

Denitrification is a microbial process that converts nitrate into gaseous nitrogen compounds. Although the final product, nitrogen gas, is environmentally benign, incomplete denitrification can release nitrous oxide. Understanding what controls this balance is essential for reducing agricultural greenhouse gas emissions.

Among the five soils, fluvo-aquic soil consistently produced the lowest proportion of nitrous oxide and showed the greatest capacity to complete denitrification to nitrogen gas. This soil contained relatively high abundances of several denitrification genes, particularly nosZ, which encodes the enzyme responsible for reducing nitrous oxide to nitrogen gas.