Assessment of fertilization strategies and policy measures for vegetables by simulation of a long-term cauliflower leek rotation

As the larger part of the residual soil nitrate in late autumn leaches out during the wet winter months, some regions monitor these residues to convince farmers to adopt improved fertilisation practices in order to reduce nitrate pollution. However, the reduction of the nitrate concentration in the surface and groundwater remains limited, especially in regions with intensive vegetable production. Soil-based advisory systems are recommended to reduce nitrate leaching, but it is unclear if this is sufficient to meet the EU nitrate directives. The objectives of this study were to assess localized fertilizer placement, soil-based fertilization, soil-based fertilizer recommendations and nitrate monitoring policies using a simulation with historical weather data. For this purpose, the ECOFERT model was proposed, a pseudo-2D expansion of the WAVE model to simulate the heterogeneity of vegetable root development. The model was calibrated and validated for a cauliflower-leek rotation on threeyear experimental data. The results show that a soil-based advisory system reduces nitrate leaching and residual soil nitrate while maintaining similar biomass production levels compared to a fixed high fertilisation rate. However, in most simulated cases, the fertilisation advice was still too high to meet the legal limits of 50 mg NO3 l-1 in the percolated water or 85 kg N ha-1 residual soil nitrate in autumn. This was attributed to considerable mineralisation and crop N-uptake variability caused by weather variation compared to fixed values. The simulations identified the potential of localised N-application and soil-based advisory systems but also showed some weaknesses. This will allow researchers to improve N-advisory systems to reduce nitrate pollution.

Automated summary

Some regions monitor the leaching of residual soil nitrate during winter months to persuade farmers to adopt better fertilization practices and reduce nitrate pollution. However, the reduction of nitrate concentration in surface and groundwater is limited, especially in areas with intensive vegetable production. This study used simulation with historical weather data to evaluate localized fertilizer placement, soil-based fertilization, recommendations, and nitrate monitoring policies. The results showed that soil-based advisory systems can reduce nitrate leaching and residual soil nitrate while maintaining similar biomass production levels, but the fertilization advice was still too high in most cases to meet legal limits.