Maize, switchgrass, miscanthus, and hybrid poplar are four of the leading crops considered as potential sources of biomass for conventional and cellulosic renewable biofuels. Many studies have investigated the evapotranspiration and soil water dynamics of these crops, but less is known about how they will affect deep drainage. More work is also needed to understand how the relationship between crop yield and water use will vary with climate. This thesis describes two studies investigating the hydrologic sustainability of these crops. The first is an observational study that makes use of yield, runoff, soil water content, and drainage measurements to estimate evapotranspiration and water use efficiency. Drainage was measured using automated equilibrium tension lysimeters. This advanced form of drainage measurement has not yet been used under this range of crops. The second study uses the Systems Approach to Land Use Sustainability (SALUS) crop growth model to simulate the response of crop yield and evapotranspiration to 30 years of variable climate. Results of these studies suggest that a) drainage under cellulosic crops will be significantly different from maize and b) climate will have a greater impact on the amount of water going to evapotranspiration than crop type.
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