Integrating site-specific biophysical and economic models to assess trade-offs in sustainable land use and soil quality

In this paper we describe the sustainability of a production system in terms of trade-offs between present and future outcomes such as crop productivity. Based on the observed site-specificity of the relationship between soil characteristics and productivity, we hypothesise that to accurately assess the sustainability of an agricultural production system we must measure the interactions between farmers’ management decisions and soil quality on a site-specific basis and then aggregate the resulting relationships. The analysis of linked, site-specific economic and biophysical models shows that soil quality at a point in space and time depends on both fixed site characteristics and on the history of farmers’ management decisions. Aggregation then shows that both on farm productivity and potential productivity are functions of parameters that define the distributions of physical and economic variables in a region. Using this result, we show that measurements of sustainability based on ‘representative’ data such as mean soil characteristics will generally be biased and thus may lead to inaccurate assessment of a system’s productivity and sustainability.