Effect of fertilizer–air-coupled drip irrigation on soil microbial carbon and nitrogen cycling functions

Abstract

To mitigate water shortages, mulched drip irrigation disrupts soil-air gas exchange, disturbing the balance between gas production and diffusion in the soil. This study explored the effects of nitrogen (N) application and aerated irrigation on the soil microenvironment, greenhouse gas emissions in the root zone, and processing tomato yields. The objective was to offer a theoretical framework and scientific evidence to guide fertilization practices, improve the soil microenvironment, and enhance crop productivity, especially under aerated irrigation. Two irrigation methods (non-aerated [A0] and aerated [A1]) and two N rates (150 kg·hm⁻² [N1] and 270 kg·hm⁻² [N2]) were tested. Results showed that aerated irrigation increased soil organic carbon (SOC), dissolved organic carbon (DOC), total nitrogen (TN), and ammonium nitrogen (NH₄⁺-N), while N application enriched soil nitrogen content. Both aeration and N application elevated N₂O and CH₄ emissions. Path analysis revealed that fertilization-coupled drip irrigation indirectly influences carbon-nitrogen cycling genes by altering soil nutrient levels, affecting greenhouse gas emissions. Soil nutrients and functional gene abundance directly impacted yield, with nitrate nitrogen (NO₃⁻-N) showing the most substantial direct effect on processing tomato yield (direct path coefficient = −1.047***). Under A1N2 (aerated irrigation with 270 kg hm⁻² N), soil nutrient levels improved (total carbon: 25.19 g·kg⁻¹, SOC: 18.25 g·kg⁻¹, DOC: 93.65 mg·kg⁻¹, TN: 0.97 g·kg⁻¹, NH₄⁺-N: 2.64 mg·kg⁻¹, and NO₃⁻-N: 1.18 mg·kg⁻¹), resulting in a yield of 32.05 t hm⁻², a 23.69% increase over increase over A0N1. Aerated irrigation combined with moderate nitrogen application is recommended for sustainable production to enhance soil fertility and crop yields. However, mitigation strategies such as nitrification inhibitors or optimized irrigation schedules should be employed to minimize greenhouse gas emissions.