Cover Crop Impacts on Runoff Hydrographs and Edge-of-Field Surface Water Quality.

Cover crops are a potential conservation practice to improve water quality of surface runoff from agricultural lands, however, effects of cover crops on runoff and water quality are dynamic due to the changing characteristics of cover crop biomass throughout the year. The objectives of this study were to i) determine cover crop impacts on runoff hydrographs related to cover crop growth and soil conditions and ii) describe how these factors influence runoff water quality. This study was conducted at the Kansas Agricultural Watershed (KAW) field laboratory near Manhattan, KS during from 2015 to 2017 in a no-till corn-soybean cropping rotation. The study included P fertilizer (0 kg P/ha, 24 kg P/ha broadcast in fall, and 24 kg P/ha injected in the spring) and cover crop (no cover crop and small grain winter cover crop) treatments in a 3x2 factorial arrangement. Treatments were applied to 0.5 ha watersheds in a randomized complete block design replicated 3 times. Watersheds were equipped with 45-cm H flumes and automated water samplers to monitor runoff and collect samples for water quality. Cover crops had a significant, but inconsistent, effect on runoff volume. Cover crops decreased the runoff volume for some events but increased it for others. Cover crops tended to have no effect or decrease the time to peak runoff and the peak runoff rate. Cover crops had no effect or increased the runoff duration. Cover crops consistently decreased the total suspended sediment concentration, which could be partially explained by cover crop impact on hydrograph characteristics.