Water Use and Hydrological Limitations of Conventional and Alternative Biofuel Cropping Systems.

Soil water regime based evaluations for crop suitability helps improve water use efficiency and water management. In crop production, physiological responses and primary productivity are directly related to available soil water in the root zone. Thus an understanding of the relationship between soil water dynamics and plant responses, both physiological and biochemical is important to determine cropping system suitability for a region.  We used automated field-to-desk TDR based systems to monitor temporal (1-hr interval) soil moisture variability in 7 different bioenergy cropping systems at the Great Lakes Bioenergy Research Center’s (GLBRC) sustainability research site at the Kellogg Biological Station in southwestern Michigan, U.S.A. Crops ranged from high-diversity perennial grass and forbs mixtures to hybrid poplar to conventionally farmed annual monocultures of corn, soybean, canola. The cropping systems were modeled using SALUS (Systems Approach to Land Use Sustainability) to obtain water use and nitrogen leaching characteristics. The results show distinct patterns of seasonal variation in root zone water availability among the different cropping systems, revealing crop water use and water uptake limitations. Significant relationships were observed between soil moisture depletion by different crops and the effect of water stress on biomass production (indicated by leaf area index) due to limited soil water supply. The overall assessment of the cropping systems for grain based and cellulosic bioenergy indicate that high biomass yielding crops such as Miscanthus, corn, and poplar can face significant water limitations.   On the other hand, cropping systems such as mixed grasses and switchgrass are less apt to have production limited by water availability.  Potential soil moisture limitation of primary productivity is an important consideration for selecting and modeling suitable bioenergy crops for a region. Land use change for bioenergy production, if it entails planning new crops with different water use than what they replace, could have considerable effects on groundwater recharge and thus on landscape hydrology.