Runoff and Erosion in No-Till Dryland Agroecosystems.
Kate Norvell, Neil Hansen, and Dwayne Westfall. Colorado State Univ, Dept of Soil and Crop Sciences, Fort Collins, CO 80523-1170
Water is the most important and limiting factor for dryland cropping systems in eastern Colorado. Tillage and crop rotation are management practices that affect the capture and storage of precipitation. No-till (NT) cropping practices increase the efficiency of precipitation storage in soil compared to conventional tillage by decreasing evaporation and increasing infiltration. However, even in intensive no-till systems only about 40% of precipitation during fallow periods is stored. Further improvements in precipitation use efficiency require a detailed understanding of the pathways of water loss from dryland agroecosystems. The importance of runoff losses during high intensity rain events in dryland cropping systems of the Great Plains is not well documented. The objectives of this study are to quantify the amounts of rainfall runoff and water erosion in NT dryland agroecosystems. Three approaches are used to evaluate runoff and erosion from a long term dryland agroecosystems study. Long term weather data is evaluated for the occurrence of rainfall events with runoff inducing intensities. Automated runoff plots were set up in Sterling and Stratton, CO in no-till Wheat-Corn-Fallow (WCF), Wheat-Corn-Millet (WCM), and Grass (G) rotations. Precipitation, runoff, and water erosion were measured on each crop for comparisons and also were averaged over rotations. Finally, computer simulation models are used to evaluate runoff and erosion risks. Runoff was highest in the corn and fallow plots and lowest in the millet, wheat, and grass plots. Corn plots were parallel with the slope and have a wider row spacing than wheat, millet, or grass. Erosion rates were low for all treatments, but were highest for corn plots. Model results are used to illustrate alternative cropping approaches to minimize runoff and maximize precipitation use efficiency.