Aerated irrigation improves soil gross nitrogen transformations in greenhouse tomato: Insights from a ¹⁵N-tracing study

Aerated irrigation (AI) significantly influences soil nitrogen (N) dynamics and biochemical characteristics, which are crucial for enhancing N absorption and utilization efficiency. However, AI's potential effects and mechanisms on gross soil N transformations remain unclear. In this study, a ¹⁵N tracing incubation experiment was conducted with four treatments, each receiving an equivalent N input (150 kg N ha^–1): (1) AINPK, chemical fertilizer under AI; (2) AIOM, organic fertilizer (OM) under AI; (3) AINPK+OM, chemical fertilizer (75 % of applied N) with organic fertilizer (NPK+OM) under AI; (4) NPK, chemical fertilizer (NPK) under traditional drip irrigation. The results revealed that AINPK significantly increased crop yield by 12.42 %, gross N mineralization by 2.58-fold, and gross nitrification by 1.27-fold compared to NPK. The AIOM and AINPK+OM significantly increased yield by 18.74–12.34 %, gross N mineralization by 1.14–1.27-fold, and autotrophic nitrification by 1.05–1.11-fold compared to AINPK. The AIOM exhibits the highest rate of NH₄⁺ immobilization, being 1.16–1.26-fold greater than the other three treatments. Moreover, AINPK significantly reduced the turnover time of organic N compared to NPK, and the turnover time of organic N of AIOM and AINPK+OM was shorter than AINPK. Overall, AI increased gross N mineralization and gross nitrification rates, enhancing soil N availability. AINPK and AIOM elevated the NH₄⁺ immobilization rates compared to NPK, while the AIOM and AINPK+OM also enhanced NO₃^– immobilization rates, stimulating inorganic N retention capacity. Therefore, based on the N transformation dynamics observed in this study, AIOM and AINPK+OM, which accelerate organic N turnover, enhance N availability and retention capacity, and increase crop yields, are recommended for crop production in greenhouse tomato.