Understanding soil nitrogen processes in diversified vegetable systems through agroecosystem modelling

Vegetable production systems are typically tillage- and input-intensive, though they may vary widely in production practices utilized. Improved understanding of soil water and nitrogen (N) processes with the use of agroecosystem models may aid in the optimization of crop yields and reduction of N losses. The objectives of this study were to (1) apply the RZ-SHAW model to diversified vegetable systems of varying production intensity, and (2) to elucidate soil N processes key loss pathways to inform opportunities for improving N cycling and sustainable intensification in these systems. The systems included conventional (CONV), low input organic (LI), and organic high tunnel (HT) vegetable systems. Soil water content and temperature were simulated well (rRMSE < 0.30) in all systems. Simulated soil NO₃¯-N content was closer to measured values in the CONV than other systems. On average, the soil NO₃¯-N content was underpredicted by 8 kg N ha⁻¹ in the 0–0.15 m, and 5 kg N ha⁻¹ in the 0.30–0.50 m soil layer in the LI system. In all systems, simulated daily N₂O flux followed the trends in the measured values, but model predicted greater peaks than measured. Nitrate leaching was the greatest N loss pathway in all systems, though timing and driving factors varied by system. Asynchrony between N mineralization and crop uptake was observed throughout the LI rotation, indicating opportunities for targeted N and irrigation inputs to increase crop yields. Simulation results indicate the need for additional study of soil microbial and N processes in HT systems.