Irrigation amount dominates soil mineral nitrogen leaching in plastic shed vegetable production systems

Flood irrigation and over fertilization lead to a large amount of nitrogen (N) leaching in conventional plastic shed vegetable production systems, resulting in low N use efficiency and huge environmental costs. Drip fertilization can significantly reduce N leaching by reducing irrigation and N application; however, the respective roles of each factor in reducing N leaching remain unknown. In this study, structural equation modeling was carried out to determine the direct and indirect relationships among factors related to N leaching in plastic shed tomato production across six consecutive growing seasons. Treatments were as follows: conventional flooding irrigation and fertilization (CIF); CIF + corn straw (CIF + C); CIF + wheat straw (CIF + W); drip irrigation and fertilization (DIF); DIF + corn straw (DIF + C); and DIF + wheat straw (DIF + W). The results showed that the most important contributing factor to N leaching in this study was water percolation, which is mainly controlled by irrigation amount. This suggests that irrigation amount has a greater effect than N input rate and straw addition. Compared to CIF, DIF significantly reduced N leaching by an average of 63.9% without compromising tomato yield, with significant increases of 52.9% and 28.1% in the water use efficiency (WUE) and partial factor productivity of applied N (PFP N ), respectively. Meanwhile, application of straw also resulted in a significant reduction in N leaching by reducing water percolation, with wheat straw having a greater effect than corn straw. Overall, excessive irrigation rather than N input was found to be the main cause of significant N leaching, highlighting the importance of optimal irrigation schemes. We therefore recommend precise drip irrigation and fertilization combined with straw addition for sustainable and environmentally-friendly plastic shed vegetable production. • Irrigation has greater effect on N leaching compared to N input and straw addition. • Water percolation and leachate N concentration were mainly controlled by irrigation. • Drip irrigation significantly reduced N leaching without compromising tomato yield. • Adding straw significantly reducing N leaching mainly by reducing water percolation.