Model-based approaches for fertilizer recommendations and their environmental impact due to nutrient leaching under variable weather conditions in open field horticultural production

Current farming practices in Flanders, Belgium use large amounts of inorganic fertilizers to attain high yield and quality. Especially in open field vegetable production the amount of applied nitrogen fertilizer exceeds the crop demand all too often. This practice in addition to the mineralization of soil organic matter and the use of organic fertilizer results in nitrate concentrations in ground and surface water that are frequently above the thresholds set by the European Union. In order to understand the impact of these legislative norms for farmers and in search of solutions for the growers, this work proposes a crop-soil-climate interaction model that enables studying the impact and interaction of weather variability and different nitrogen fertilization schemes on yield and environment for open field cauliflower and leek production systems. Data gathered over a period of 3 years in a specifically designed field experiment resulted into the development of two crop growth modules able to simulate the day-to-day biomass accumulation of a cauliflower and leek crop. A transport model for soil water and solutes that simulates soil nitrogen and carbon dynamics was adapted to the specific root distribution characteristics of these horticultural crops and adjusted to take into account common fertilizer practices of the production system at hand. Calibration results of the model parameters are presented and historical weather data was used to assess the variable impact of past weather conditions on a continuous annual cauliflower-leek production scheme. Besides the effect on crop production, the model was also able to calculate the year-to-year effect on the soil water and nitrogen balance. Subsequently, different fertilizer application scenarios were developed and used to determine the production cycle outcomes in terms of biomass production success in combination with soil nutrient losses and potential environmental impact. Broadcast, row applied and fertigation applications at different fertilizer rates were analysed in search of management solutions that assure adequate production levels without jeopardizing the surroundings. An assessment was made that determined the residual soil nitrate content by the end of the production cycle in order to evaluate the feasibility of these fertilizer strategies of compliance with the obligatory maximum threshold value of 90 kg N/ha (residual nitrate) as enforced by the government. The different fertilizer scenario simulations gave a clear indication of production limits and the model allowed the estimation of plausible production outcomes under variable weather. These outcomes were used to generate on-the-go information for pre-season decision support and in-season managerial recommendations, and included a real-time estimation of the likeliness of not complying with the environmental threshold under present weather conditions. Finally, the presented model allowed determining optimal fertilizer strategies and defining best-bet solutions to the growers depending on the production priorities.status: publishe