Modelling agricultural management systems with APEX.

Abstract

Abstract The objectives of this chapter are to describe the major components of the Agricultural Policy Environmental eXtender (APEX) model and demonstrate its application using a case study for evaluating agricultural management practices for a 104 km1 sub-watershed within the Bosque River watershed in central Texas, USA. The Bosque River eventually drains into Lake Waco, which serves as the primary drinking water supply for the greater Waco area and provides water for agricultural production, recreational fishing and swimming. The watershed is facing a suite of water quality issues resulting from sediment, nutrient and bacterial loadings which are potentially derived from improperly managed cropland and grazing land, and from applied dairy waste and effluent discharge from waste water treatment plants. The study sub-watershed is predominantly crop land. The APEX model was to be calibrated and validated for monthly stream flow, sediment yield and nutrient losses at a monitoring station within the sub-watershed, and the calibrated model was then used for long-term scenario analysis to evaluate the benefits of alternative agricultural management practices.