Reducing nitrogen application through deep placement to optimize the nitrogen balance in a dryland maize cropping system

Abstract

Estimating nitrogen (N) balance in croplands is critical for optimizing N management and promoting sustainable agriculture. Deepening N placement while reducing application rates offers a promising strategy to improve N balance, but remains underrepresented in field studies, especially in semi-arid regions. Here, we used a two-year field experiment combining three N rates [conventional (225 kg N ha⁻¹) and two reduced rates (191 and 158 kg N ha⁻¹, representing 15 % and 30 % reductions)] with four placement depths (5, 15, 25, and 35 cm) to assess their interactive effects on N balance in dryland maize systems. We quantified N inputs (seed, fertilization, atmospheric deposition), outputs (crop uptake, NH₃ volatilization, N₂O emissions, and leaching), and soil N retention over two growing seasons with contrasting rainfall patterns. Reducing N inputs generally decreased gaseous N losses, crop N uptake, and grain yield, ultimately lowering overall N balance. Regardless of application rate, deep N placement significantly reduced gaseous N losses and improved crop N uptake compared to shallow placement (5 cm), effectively compensating for yield losses due to reduced N application. A 15 % N reduction combined with 25 cm placement resulted in the lowest N balance and highest economic return by minimizing both gaseous and hydrological N losses. This combination also increased crop N uptake and grain yield by 13.8 % and 12.5 %, respectively, relative to the conventional practice. Moreover, deep placement with reduced N demonstrated greater resilience to extreme rainfall, helping to stabilize N balance. These findings highlight the potential of optimized placement depth to reduce N use while enhancing environmental and economic benefits.