A spatially explicit assessment on the carrying capacity of livestock under minimum feed imports and artificial fertilizer use in Dutch agriculture

CONTEXT: Current agricultural systems in the Netherlands and other parts of Europe depend on large quantities of nutrients from imported feed and artificial fertilizers. This may result in unwanted nutrient accumulation and losses and negative environmental impacts. One way of making these systems more sustainable is to balance livestock numbers with the local feed supply and nutrient requirements for crop production. However, there is currently limited quantitative- and spatially-explicit insight into the effects of reduced imports on livestock numbers and nutrient balances. OBJECTIVE: The aim of this study is to quantify the number of livestock that can be sustained when minimizing nitrogen (N) imports of feed and artificial fertilizers into Dutch agriculture. METHODS: We developed a spatially-explicit mathematical programming model to optimize livestock numbers in different scenarios of allowed N imports. The model takes into account current flows of nutrients, related to nutrient supply from livestock manure, feed and fodder, and nutrient requirements in agricultural production. RESULTS AND CONCLUSIONS: Minimizing N feed imports and artificial N fertilizer use under current land use resulted in an overall reduction of livestock density of 57.4% compared to the current livestock density based on 2020 activity data. In addition, it led to an increase in artificial N fertilizer inputs of 20.5% to maintain the N requirements of agricultural land. In contrast, focusing on minimizing artificial fertilizer use led to a reduction in livestock density of 25.8% compared to the current livestock levels. Depending on the scenario, we found strong regional variation in nutrient balances and livestock numbers. For instance, while currently the application rates of artificial fertilizers and livestock manure are relatively constant in space, this was no longer the case when N import in the form of feed was minimized. In that case, the crop-dominated areas showed a deficit in livestock manure and a substantial increase of artificial fertilizers. SIGNIFICANCE: The presented model allows for assessing spatially explicit impacts of reduced N imports of feed and artificial fertilizers on livestock density. Using the Netherlands as case study, we show that reducing feed imports is a more effective leverage point to reduce N surplus and external N inputs into agriculture as compared to when reducing artificial fertilizer use. Our findings can inform the development of area-specific strategies that are aimed at reconnecting livestock and agricultural land.