This study utilized state-of-the-art measurements of nitrogen isotopes to evaluate nitrogen cycling and to assess the biological sources of the potent greenhouse gas, N₂O, in response to water-saving practices in rice systems. Water-saving practices did emit more N₂O, and high N₂O production had a lower ¹⁵N isotope signature. Modeling and visual interpretation indicate that these emissions mostly came from denitrification or nitrifier denitrification, controlled upstream by nitrification rates.