Optimal Nitrogen Management Enhanced External Chemical Nitrogen Fertilizer Recovery and Minimized Losses in Soil-Tomato System

Excess chemical nitrogen (N) fertilization is widespread in intensive greenhouse vegetable production in China and has resulted in low recovery efficiency and high losses of chemical N fertilizer. Understanding the fate of chemical N fertilizer is crucial for best management of chemical N fertilizer. Using the technique of stable isotope 15N-labeled urea, a micro-plot experiment was conducted to estimate the recovery of 15N-labeled urea in tomato, residues in soil and losses in soil-tomato system. The treatments included the conventional N management with chemical N rate (1000 kg N/ha), named FP and optimal N management with chemical N rate (500 kg N/ha), combined with maize straw and drip irrigation, named OPT. Compared with the FP, total dry matter yield increased by 6.5%–9.3% for the OPT in the autumn-winter season (AW) and winter-spring seasons (WS), respectively. There was a significantly higher recovery efficiency (20.7%) of 15N-labeled urea in the OPT compared to the FP (11.3%; P < 0.05). The amount of residual NO3--N derived from 15N-labeled urea was significantly higher in the FP than in the OPT (P < 0.05). More inorganic N derived from 15N-labeled urea was incorporated into the stable fraction of organic matter in the OPT and had a positive effect on reducing the N leaching with increased time during the season. The loss rate of N derived from 15N-labeled urea was 46.8% in the FP, 25.8% greater than in the OPT. Optimal N management improved tomato yields, enhanced chemical N recovery efficiency, while minimizing losses in the soil-tomato system. It will be practical for maintaining the sustainability of greenhouse-based intensive vegetable systems.