Reducing nitrogen leaching in a subtropical vegetable system

Nitrogen (N) leaching is considered a substantial problem in South China vegetable production because of the heavy rainfall and the excessive application of N fertilizer, but quantitative data and effective countermeasures are lacking. A systematic approach to reducing N leaching while maintaining or increasing vegetable yields is urgently needed. A 2-year field study was conducted to quantify N leaching in a subtropical vegetable system (bitter gourd, Momordica charantia L.) in South China and to evaluate how leaching is affected by the following three N management strategies: zero N application (Nno, 0 kg N ha−1), conventional N management (Ncon, 377 kg N ha−1, with NH4+), and optimized N management (Nopt, 300 kg N ha−1, with a combination of NH4+ and NO3− at a reduced rate plus nitrapyrin, a nitrification inhibitor). Lysimeter data indicated that 139 kg N ha−1 per growing season was lost by leaching with Ncon, this represented 36% of the N applied. With Nopt, leaching was reduced by 27.1%, and yield was increased by 25.1%. A combination of NH4+ and NO3− plus nitrapyrin at a reduced rate increased plant N uptake, maintained a high NH4+/NO3− ratio in the soil, and thereby reduced leaching. The alternative N management strategy exemplifies a new way to achieve high yields with low environmental costs in intensive vegetable production systems.