Simulating variable fertilizer application ‘rates’ of synthetic and bio-based fertilizers in potato and maize fields to optimize nutrient management and validate environmental sustainability

Agricultural systems are inherently complex, as they are influenced by the interlinkages between biological, physical, and chemical processes, alongside uncontrollable factors such as weather and soil conditions. To overcome these challenges, dynamic system models have emerged as indispensable tools that can be effectively implemented in precision agriculture. Such dynamic models enable the optimization of variable-rate fertilization and, consequently, enhance crop management strategies while fostering environmental sustainability.

Given the significant increase in fertilizer use over the past decades, there is an ongoing effort to enhance better nutrient management and sustainable development in agriculture within the European Union. This includes the integration of nutrient recovery technologies, such as anaerobic digestion (AD) that converts organic waste into bio-based fertilizers, helping mitigate excessive nutrient loss in Nitrate Vulnerable Zones (NVZs). Additionally, introducing circularity into the fertilizer production system offers a viable solution by replacing the traditional, emission-intensive nitrogen fertilizer production methods with innovative, low-emission alternatives. However, improper application of these pre-processed fertilizers can lead to environmental issues, such as N and/or phosphorus leaching and greenhouse gas (GHG) emissions. Therefore, it is essential to (i) select the right product with least N loss (via leaching or emissions) to the environment among selected (ammonium sulphate, pig urine, liquid fraction of digestate and mineral concentrate) pre-processed bio-based fertilizers, (ii) opt the right application techniques (injection, drag hose, spraying, etc.) available for the variable-rate fertilization, (iii) provide farmers with the best optimal rate and timing for performing precision applications under changing climate.

To address this issue, we implement the CANDY (Carbon And Nitrogen DYnamics) model in a site-specific manner. The model is applied to ongoing field experiments in maize and potato fields (2023–present) at the 3-hectare Bottelare research farm, as well as two commercial farms in Lamstraat and northwest France (2.7 and 8 hectares, respectively). Different application rates of selected bio-based fertilizers (ammonium sulphate, pig urine, liquid digestate, mineral concentrate) are simulated for soil mineral and organic nitrogen (minN, SON), soil organic carbon (SOC), nitrous oxide (N2O) emission dynamics, and validated with observed values from soil properties (e.g. NH₄/NO₃, OC, etc.) and GHG measurements (N₂O, CO₂). This provides valuable data-driven insights of potential mitigation measures regarding N losses and further can be used to inform stakeholders (i.e. farmers).