This article presents a modelling system for synthesising heterogeneous productivity and nutrient loading potentials inherent in agricultural cropland for policy use. Phosphorus abatement cost functions for cropland farmers in a southeastern Minnesota watershed are metamodelled using frontier analysis. These functions are used to evaluate policies aimed at reducing non point phosphorus discharges into the Minnesota River. Results indicate an efficiently targeted policy to reduce phosphorus discharge by 40% would cost US$ 167,700 or 844 per farm. © 2003 Elsevier B.V. All rights reserved.