Dilemmas in circular agriculture: A spatially explicit optimization of nutrient flows

Circular agriculture is widely regarded as a promising strategy for reducing environmental impacts of agriculture. Using optimization modelling, this dissertation examines how different strategies for improving and localizing the reuse of residual biomass and nutrient streams affect the spatial distribution of agricultural systems, environmental pressures, and costs. It further analyses the trade-offs between these objectives across different regions in the Netherlands. A central finding is that spatial variability is a key factor influencing the trade-offs between agricultural circularity on the one hand and environmental and economic objectives on the other. Reducing external nitrogen inputs had clear spatial consequences: lower feed imports led to shifts in livestock densities, manure allocation, and land use across regions. Furthermore, improved nutrient recovery from manure changed the spatial distribution of mineral fertilizers and recovered nutrient products. These changes affected nutrient losses and emissions differently across regions, depending on livestock type, location, manure processing methods, and local agroecosystem characteristics such as soil type and land use.