Soil erosion and nonpoint-source pollution control in an Idaho watershed

Abstract

A geographic information system was used to assemble and retrieve the physical parameters required to estimate sheet and rill erosion and water quality effects of applying 11 resource management systems to 16 farms in Idaho's Tom Beall watershed. A linear programming model was used to determine the economically efficient (optimal) systems for reducing total erosion and nonpoint-source pollution in the watershed. The water quality effects of the optimal resource management systems were evaluated using the Agricultural Nonpoint Source (AGNPS) model. Minimum tillage with either cross-slope farming or contour farming was the most economically efficient system for reducing farm-level erosion rates. All but two farms had to switch from conventional to minimum tillage to reduce the average erosion rate in the watershed to the tolerance (T) level [11.2 t/ha/yr (5 tons/acre /year)]. Reducing average erosion to 2T required using no tillage practices on 11 farms and converting two farms to permanent vegetation. Total net farm income in the watershed increased 1.5% when average erosion was reduced to T. Controlling erosion significantly reduced total sediment, nutrients (nitrogen and phosphorus), and chemical oxygen demand (COD). Average sediment, nutrients, and COD decreased 45%, 38%, and 24%, respectively, with the optimal resource management systems for 2T, and 72%, 64%, and 29%, respectively, with the optimal systems for T.