Runoff and Erosion Estimates for Great Plains Dryland Agroecosystems

Water is the most production limiting factor for dryland cropping systems in semiarid Great Plains environments. Evaporation is responsible for the greatest amount of water loss and management practices such as notill have been adopted to reduce evaporative losses. Less is known about the magnitude of water loss due to runoff. An objective of this study is to estimate an expected range in rainfall runoff in dryland agroecosystems and the potential for improving precipitation use with management practices that reduce runoff. Another objective was to estimate soil-water erosion associated with runoff. The approach coupled an analysis of historical hourly rainfall intensity data and field measurements of runoff and erosion from dryland agroecosystems study sites in Sterling and Stratton, Colorado. Rainfall analysis was used to determine the frequency and quantity of high intensity rainfall expected to generate runoff. Runoff was estimated based on assumed fractions of high intensity rainfall for variable management and climate conditions and based on field observations at the same sites. Runoff was estimated to range between 8 mm for drought years and management with good surface protection to 80 mm for years with above average precipitation and management with poor protection of the soil surface. There is the potential to capture as much as 60 mm of precipitation through improved management practices, a quantity that can increase crop yield and profitability. Annual rates of erosion by water were estimated to range between 1 and 9 Mg ha. Under management with poor surface protection, soil erosion rates in dryland cropping systems are too high to sustain crop production, while management that protects the soil surface and reduces the probability of runoff is an effective means of soil erosion control. Residue management achieved through no-till or minimum till practices is the most effective means of soil erosion control and sustaining dryland agriculture in the semi-arid Great Plains will depend on adoption of these practices.