Switchgrass based bioenergy production has been considered a feasible alternative of land use for the mixed-grass prairie and marginal croplands in the High Plains. However, little is known of the effect of this land use change on the water cycle and associated sediment output in this water controlled, recharge deficient ecosystem. We quantified individual components of the water cycle and associated sediment output using paired watersheds at the USDA-ARS Southern Plains Range Research Station in Western Oklahoma. We used one native mixed-grass prairie watershed as a control and the other was undergoing conversion to switchgrass production in spring 2009. The runoff and sediment output were quantified using flumes and automatic sediment samplers. Water storage in the soil was calculated based on measurement of soil water content from ECH₂O EC-5 sensors at multiple depths, and deep drainage was measured using the hydraulic gradient approach and Gee passive capillary lysimeters.

Results/Conclusions

Our preliminary results indicated a substantial difference in the temporal dynamics of soil water contents in the soil profile between the control watershed and the watershed under switchgrass conversion. The herbicide treatment and associated reduction in grass cover and biomass in the switchgrass conversion watershed resulted in a greater range of fluctuation in soil water contents through the entire soil profile and higher water contents for the soil layers from 80 to 120 cm. There were somewhat different responses of runoff, evapotranspiration, and deep drainage potential for each treatment.