Soil-Water Dynamics, Evapotranspiration, and Crop Coefficients of Cover-Crop Mixtures in Seed Maize Cover-Crop Rotation Fields. II: Grass-Reference and Alfalfa-Reference Single (Normal) and Basal Crop Coefficients

Abstract

Cover crops have been gaining attraction in agriculture as rotational crops because of their potential benefits in various soil characteristics and soil-water functions. The knowledge about cover-crop water use in terms of examining the water availability for the next field crop is very important for developing and implementing sustainable agricultural management strategies. Crop coefficients for estimating water use for cover crops are among one of the least available coefficients of any cropping systems. In this study single (normal) and basal grass-reference (Kco and Kcbo) and alfalfa-reference (Kcr and Kcbr) crop coefficients were developed as a function of cumulative growing degree days (CGDD) for (1) cover-crop mixes (CC) only, (2) seed maize cover-crop rotation (SCCC), (3) seed maize residue without cover crop (SC), and (4) bare soil. The research was conducted for three cover-crop growing seasons (2012–2013, 2013–2014, and 2014–2015) on three center pivot–irrigated seed maize cover-crop rotation fields (F1, F2, and F3) near Beaver Crossing, Nebraska. Single and basal crop coefficients were developed from the ETa data and estimated grass-reference and alfalfa-reference evapotranspiration (ET0 and ETr). The Kco and Kcr values exhibited interannual variability for the same months and treatments between the years. The Kco and Kcr varied from 0.0 to 1.8 and 0.0 to 1.2, respectively, in the 2012–2013 season; from 0.0 to 2.3 and 0.0 to 1.7, respectively, in the 2013–2014 season; and from 0.0 to 2.3 and 0.0 to 1.7 in the 2014–2015 cover-crop growing season. On average, the cover crop Kcbo and Kcbr values fluctuated between 0.0 to 1.6 and 0.0 to 1.5, respectively. In general, depending on the treatment, maximum Kc and Kcb values occurred at CGDD between approximately 980 and 1,300°C (end of October), which then gradually decreased in the winter months. Minimum Kc values usually occurred at CGDD of approximately 200°C. The Kc and Kcb curves presented in this study are among first cover crop Kc values and can be used to estimate cover crop ETa for particular cover-crop mixtures that are similar to those used in this research and grown under climatic conditions similar to the research area.