Returning corn stalks to the field is an important and widely used soil management practice which is conducive to the sustainable development of agriculture. In this study, the effects of corn stalks and urea on N₂O production in corn field soil were investigated through a 21-day incubation experiment. This study showed that increasing amounts of urea added to soil with a history of corn cultivation leads to increasing overall N₂O emissions, by increasing both the intensity and the duration of emissions. Although N₂O production was affected primarily by urea-derived NH₄⁺-N and NO₃⁻-N, its main source was native soil nitrogen, which accounted for 78.5 to 94.5% of N₂O. Returning corn stalk residue to the field reduced the production of N₂O, and the more urea was applied, the stronger the effect of corn residue on reducing N₂O emissions. Combining the application of corn stalks and urea could reduce the concentration of NH₄⁺-N and NO₃⁻-N derived from urea, and then reduce the substrate required for N₂O production in nitrification and denitrification processes. In addition, the combined application of corn stalks and urea could effectively inhibit the abundance of key N₂O-producing genes AOA amoA, nirS and nirK.

Reducing greenhouse gas (GHG) emissions and ammonia (NH₃) volatilization by improving fertilization methods to increase crop yield is beneficial for the green and sustainable development of agriculture. This study evaluated the effects of farmer practice fertilization (FP), nutrient expert optimized fertilization (NE—optimized fertilizer usage and time), the application of stable compound fertilizer (SF), and the application of controlled-release coated urea (CRU) on greenhouse gases, NH₃ volatilization, and corn yield through field experiments set up in the corn planting area in western Liaoning Province. The results showed that compared with FP treatment, NE could significantly reduce NH₃ volatilization by 28% and increase N₂O release by 41%. Compared with FP treatment, SF could significantly reduce NH₃ volatilization by 48.54%, N₂O release by 38.54%, CO₂ release by 13.96%, global warming potential (GWP) by 16.60%, and greenhouse gas emission intensity (GHGI) by 27.23%, and could significantly increase corn yield by 15.86%. Compared with FP treatment, CRU could significantly reduce NH₃ volatilization by 63.46%, CO₂ release by 11.98%, GWP by 10.73%, and GHGI by 13.77%, while increasing N₂O release by 6.71%. Overall, NE, SF, and CRU treatments all showed better effects than FP treatment in increasing corn yield or reducing NH₃ volatilization and GHG emissions. Among them, SF treatment demonstrated superior performance over NE and CRU treatments in terms of NH₃ volatilization, corn yield, and GHGI. Therefore, the application of stable compound fertilizer is the optimal choice for corn planting in western Liaoning, with broad application prospects.

The denitrification process is the main process of the soil nitrogen (N) cycle in paddy fields, which leads to the production of large amounts of nitrous oxide (N₂O) and increases N loss in paddy soil. Plant-derived bio denitrification inhibitor procyanidins are thought to inhibit soil denitrification, thereby reducing N₂O emissions and soil N loss. However, the denitrification inhibition effect of procyanidins in paddy soils with high organic matter content remains unclear, and their high price is not conducive to practical application. Therefore, this study conducted a 21-day incubation experiment using low-cost proanthocyanidins (containing procyanidins) and paddy soil with high organic matter content in Northeast China to explore the effects of proanthocyanidins on N₂O emissions and related microorganisms in paddy soil. The results of the incubation experiment showed that the application of proanthocyanidins in paddy soil in Northeast China could promote the production of N₂O in the first three days but inhibited the production of N₂O thereafter. Throughout the incubation period, proanthocyanidins inhibited the enzyme nitrate reductase (NaR) activity and the abundance of nirS and nirk denitrifying bacteria, with a significant dose-response relationship. Although the application of proanthocyanidins also reduced the soil nitrate nitrogen (NO₃⁻-N) content, the soil NO₃⁻-N content increased significantly with increasing incubation time. In addition, the application of proanthocyanidins increased soil microbial respiration, ammonia-oxidizing archaea (AOA) amoA gene abundance, and soil ammonium nitrogen (NH₄⁺-N) content. Therefore, the application of proanthocyanidins to paddy soil in Northeast China can effectively regulate denitrification. However, in future studies, it is necessary to explore the impact of proanthocyanidins on the nitrification process and use them in combination with urease inhibitors and/or nitrification inhibitors to better regulate soil N transformation and reduce N₂O emissions in paddy soil.