Implications of Biofuel-Induced Land Use Change and Management on Irrigated Agriculture in the Texas High Plains

Texas High Plains (THP) is one of the important cotton (Gossypium hirsutum L.) growing regions in the US. Agriculture in the THP faces several challenges from declining groundwater levels and deteriorating groundwater quality in the underlying Ogallala Aquifer, and recurring droughts and severe wind erosion. Groundwater conservation districts in the THP have started setting up limits on annual allowable groundwater pumping for irrigation. Introducing cover crops in to the cotton production systems in the THP and/or changing land use from cotton to perennial bioenergy crops could not only address the above challenges, but also assist in meeting the national biofuel target. The overall goal of this study is to assess the implications of biofuel-indced land use managemt (growing winter wheat as a cover crop along with cotton) and land use change (replacing cotton with Alamo switchgrass (Panicum virgatum L.) and Miscanthus (Miscanthus giganteus)) on hydrology, water quality, wind erosion and biofuel production potential in the Double Mountain Fork Brazos watershed in the THP using the Agricultural Policy/Environmental eXtender (APEX) model. Results showed that, in comparison to the baseline (cotton monoculture) scenario, the average annual wind erosion reduced by 59% and 37% in irrigated and dryland areas, respectively, when winter wheat was grown as a cover crop along with cotton under the current 18-inch groundwater pumping restriction set up by the High Plains Water District. In addition, winter wheat produced about 2.6 and 2.0 Mg ha-1 of biomass for biofuel purposes under the irrigated and dryland conditions, respectively. Furthermore, the total nitrogen (TN) load and nitrate-nitrogen (NO3-N) leaching decreased by more than 43% and 73%, respectively, under the cover crop scenario. The land use change from cotton to switchgrass (in irrigated areas) and Miscanthus (in dryland areas) decreased the TN load, NO3-N leaching and wind erosion by more than 89% relative to the baseline. Under the restrictions on groundwater use, when compared to single harvest, multiple harvests of perennial bioenergy crops (two- and three-harvests in case of switchgrass and Miscanthus, respectively) were found to be better in terms of biomass production (> 20 Mg ha-1), and protection of groundwater and soil quality.