A procedure to derive land quality indicators for sustainable agricultural production

A land quality indicator, defined as a ratio between actual and potential production of wheat under Dutch conditions with acceptable leaching of nitrates and risks, is proposed. Production was simulated for 30 years, expressing temporal weather variability, using a wide range of nitrogen fertilization scenarios and including nitrate leaching to the groundwater. Yields were calculated considering probabilities ('implied risks') that yield potentials were not reached and that nitrate leaching exceeded environmental threshold values. Calculations were made for a prime agricultural soil in the Netherlands (loamy, mixed, mesic Typic Fluvaquent) comparing fields having had long-term organic- and conventional management. Quality indicators were consistently higher for the land with organic management. The proposed calculations are reflected in a graph with production and associated nitrate leaching rates and their probabilities of exceedance. The graph provides a framework. A single land quality indicator can be derived only after decisions on risk acceptability have been made. (C) 1998 Elsevier Science B.V. All rights reserved.