Persistent Ammonia Volatilization Under Conservation Tillage and Slow-Release Fertilization

Ammonia (NH3) emissions from fertilized cropland are influenced by conservation tillage practices, yet the underlying mechanisms remain insufficiently understood in the black soil region of northeastern China. In this study, field observations were conducted in a maize cropland to compare NH3 volatilization under conventional tillage, no-tillage, and straw incorporating treatments following application of urea and slow-release fertilizer. Results showed that compared with conventional tillage, no-tillage-straw mulching (T1) and ridge tillage-straw mulching (T3) treatments significantly reduced soil temperature while increasing soil moisture and decreasing the estimated soil resistance to NH3 transport. These changes were accompanied by higher NH3 emission factors (EFs) in the T1 and T3 treatments, although differences in EFs among tillage treatments were not statistically significant. Compared with urea, slow-release fertilizer delayed the occurrence of peak NH3 volatilization and reduced cumulative NH3 emissions by approximately 54%. Notably, measurements under slow-release fertilizer application revealed that elevated NH3 volatilization persisted for more than 40 days after fertilization, indicating that conventional monitoring periods may underestimate cumulative NH3 losses in conservation tillage systems using slow-release fertilizers. Overall, conservation tillage substantially altered soil environmental conditions associated with NH3 volatilization, while fertilizer types strongly influenced the temporal dynamics and magnitude of NH3 emissions. These findings provide useful insights for improving NH3 emission monitoring, process understanding, and inventory estimation in conservation tillage systems.