Water Requirements and Economics for Growing Perennial Warm-Season Grasses for Ethanol Under Irrigation in the Arid-West

Non-Technical Summary: The potential is tremendous to produce bioenergy from cellulosic perennial warm-season grasses under irrigation in the arid-west. Selected biomass grasses are long-lived perennials, that require less chemical inputs, that will reduce wind and water erosion, and provide feedstock for multiple bioenergy uses. This study investigates how much irrigation water these future biofuel crops require. Our hypothesis is that these grasses require less water than we have applied in research trials and less than future bioenergy growers may believe is necessary. Our desired outcome is saving precious water for human, food and other societal needs while economically and sustainably growing high water use, efficient perennial grasses for biofuel to supplement the nation's energy supply. <P> Approach: Biomass yield of perennial warm-season grasses occurs in the second and subsequent production years and are equal to or greater than irrigated annual biomass producing crops. Unlike annual biomass crops, water requirements of the perennial grasses are not well defined. By understanding their water requirements and responses under limited irrigation we can analyze the irrigated arid-west's capability to sustainably produce these perennial grasses to help satisfy our nation's energy needs. This project will be conducted at two very different climates in the irrigated arid-west: Arizona (320 N latitude and 1100 W longitude) and Washington (460 N latitude and 1190 W longitude). Grasses include switchgrass, Kleingrass, big bluestem, Eastern gamagrass and Indiangrass. A core of three grasses with identical varieties will be planted at both locations with additional grasses planted that may be more adapted to the different latitudes. In all cases, grasses will be harvested at bioenergy maturity rather than managed as forage. Biomass samples will be collected, weighed, oven dried and ground for quality and ethanol NIRS prediction. Grasses will be established and irrigated using continuous move irrigation systems. During the establishment year all plots and grasses will be fully irrigated to ensure uniform and productive stands. In the second and following years four irrigation treatments, based on evapotranspiration (ET) will be imposed. The four treatments will be: 1) full irrigation or 100% ET, 2) 80 to 85% ET, 3) 60 to 65% ET, and 4) 30 to 35% ET. The irrigation treatments will be applied by varying the travel speed using precision control methods. Neutron access tubes will be placed into each plot during the establishment year. The water content in the soil profile will be read in each tube at the beginning and end of each season in order to close the soil-water balance. The economics of transitioning to bioenergy crops in this region will be analyzed using standard accounting procedures for farm management cost and return estimates. These procedures involve documenting field operations, including detailed information on farm machinery operations and input usage. Farm size, crop rotation, age and type of equipment, soils, and quality of management all influence profitability. We will specify production assumptions so growers can develop budgets for their farms. All resources are valued at market price or their opportunity cost. An opportunity cost is represented by what is foregone by using a particular resource rather than renting it out. In this way, farmers can determine if their businesses are truly sustainable, i.e. if they will be profitable. The experimental design is a replicated split plot with irrigation treatments as whole plots and grass species/cultivars as subplots. Species/cultivars and irrigation treatments will be analyzed as fixed effects while years and replications will be random effects. Data will be subjected to analysis of variance using the procedures of SAS. Means will be separated after a significant protected F-test from Type III Sums of Squares.