Globally, there is a growing interest in producing cellulosic ethanol from biomass. For sustainable production of biomass for energy, it is essential to better understand the interaction between bio-energy cropping systems and the available water resources. Studying this interaction requires a complete analysis of the water balance. Change in soil water storage is one of the important components of the water balance that affects plant growth.  The objective of this research is to determine the effects of two bio-energy cropping systems, with two different nitrogen managements on the dynamics of soil water depletion. A split plot study is being conducted at Stillwater, OK, where the main plots are no-till switchgrass and high biomass sorghum and the subplots are 85 kg/ha of N and 0N plus winter legume. Neutron access tubes have been installed in each plot. Soil water content is measured weekly using neutron moisture meter to a depth of 2 m. We hypothesize that the perennial system will exhibit greater early-season soil water depletion compared to the sorghum. We also hypothesize that the winter legume subplots will exhibit greater early season soil water depletion than the subplots receiving nitrogen fertilizer. Results from the 2011 growing season will be presented in this poster.