Simulation of Soil Loss and Available Water Content to Assess the Sustainability of Selected Farm Practices

Abstract

ABSTRACT One consequence of unsustainable farming practices is considered to be the deterioration of soil quality; however, finding a measure of soil quality in relation to sustainability has proven elusive. Defining soil quality in terms of productivity is problematic because of the numerous factors affecting productivity, including use of managed inputs that can mask soil deterioration. This paper explores, as one measure of soil quality, the consistency of the soil water content available for crop growth. By comparing soil water content under different cropping practices with that for a known sustainable system, a mature forested soil, we show how variation in water content can be used as an indicator of sustainability. The model CENTURY was used to simulate changes in soil organic matter content over time, and the Generalized Watershed Loading Function was used to simulate soil erosion and fluctuations in water content. Effects of soil type, initial soil organic matter content, slope, cropping system, tillage, and manure application were considered. Generally, only small differences were predicted in the mean available water content among these systems, but the coefficient of variation in available water content was higher in the cropped systems than in the mature system. Systems with higher rates of soil erosion also exhibited greater variability in available water content. This finding suggests that variability in available water, as compared with that of a mature system, is an indicator of the sustainability of farm practices.