Groundwater Recharge Characteristics and Subsurface Nutrient Dynamics Under Alternate Biofuel Cropping Systems in Wisconsin

High yielding cropping systems are proposed to supply feedstock to the latent cellulosic ethanol industry. Assessing the sustainability of these systems requires a better understanding of water, sediment, and nutrient export dynamics when these systems are managed for biofuel production. Using intensive field experiments comprising eight different alternative biofuel production systems already established as part of the Sustainability Thrust of the Great Lakes Bioenergy Research Center, we will generate information as to how cropping system diversity & productivity condition and influence subsurface water/nutrient loss dynamics at varying spatial scales. The major goal of the proposed work is to determine the groundwater recharge quality and quantity impacts of proposed changes in cropping systems for biofuels production. Specific objectives are to: Quantify subsurface downward water (groundwater recharge) and nutrient fluxes across varying spatial (plot- to field-scales) and temporal (single rainfall event to seasonal) scales under the proposed alternate biofuel production systems; Link the diversity and composition of species, functional groups, and cropping systems to water and nutrient dynamics; and Scale results to heterogeneous landscapes and determine long-term impacts using APEX (Agricultural Policy Environmental eXtender) model simulations. Instrumentation including equilibrium tension lysimeters, passive capillary wick lysimeters, soil moisture sensors, and soil solution samplers will be installed to monitor and quantify water and nutrient fluxes at selected field sites. Simulated rainfall experiments, which will provide control over important rainfall parameters (intensity and duration), will be performed to obtain plot-scale measurements. Subsurface fluxes from these experiments will be compared with those obtained from natural rainfall obtained throughout the growing seasons. Subsurface soil solution and drainage samples will be analyzed for dissolved N, organic C, and phosphorus (P). Unique datasets generated in this study for alternate biofuel production systems will be used to calibrate the APEX model, which will then be used to perform long-term simulations.