Development of ReturN, a manure redistribution optimisation tool: Description and application context

CONTEXT: Collaborative agreements for manure management would enable intensive and specialized livestock farms to expand the agricultural area available for manure distribution by transporting manure to arable farms, thus increasing nitrogen and carbon recycling, reducing environmental pollution and decreasing farms' dependence on external inputs. The economic and environmental viability of such collaborative arrangements depends on the balance between the manure transport costs and emissions (and thus the distances between farms) and the saving in mineral fertiliser purchase costs and production emissions. OBJECTIVE: The objective of this study is to present a software tool (ReturN) designed to assess the opportunities for moving he nitrogen (N) in manure from locations where the amount exceeds the utilization capacity of the crops to locations with spare utilization capacity. ReturN allows the optimisation of manure fluxes at a local or regional scale, on the basis of a multi-criteria balance that considers both economic and environmental criteria. The tool is applied in three European case studies thus showcasing the tool applicability options. METHODS: The ReturN multi-criteria balance considers manure transport costs and emissions (and thus the distances between source and recipient locations) and the saving in mineral N fertiliser purchase costs and production emissions. The locations among which manure-N fluxes are optimised can be farms or municipalities, based on the aggregation level of the manure data. The tool outputs, linked to each flux of manure from a source to a recipient location, are the amount of transported N, the monetary costs, and the associated fossil carbon dioxide (CO2) emissions. The ReturN tool was applied to the optimisation of manure fluxes in 3 real European case studies, and the sensitivity of its outputs to parameters was assessed using the modified Morris sensitivity analysis method. RESULTS AND CONCLUSIONS: The application of the ReturN tool successfully optimised manure-N redistribution under varying conditions of deficits and surpluses and for different geographical areas shapes. The reduction in costs associated with the purchase of mineral N fertilisers and the decrease in fossil CO2 emissions (due to the transportation of manure and the production of mineral N fertilisers) achieved through the optimisation of manure-N fluxes were found to be primarily dependent on the initial manure surplus condition and secondly on mineral N fertiliser price and manure characteristics (density and N concentration). SIGNIFICANCE: The flexibility of the ReturN tool's settings, along with its limited input requirements, ensures its suitability for direct application by end users in practical contexts thus enabling both the economic and environmental assessment of the cost-effectiveness of manure transport.