Impacts of alternative biomass cropping systems and landscape position on soil moisture dynamics
Rising interest in the use of biomass crops to meet global bioenergy needs has raised concerns about the potential environmental impacts associated with their broad-scale deployment. Through a randomized, replicated block experiment, known as the Landscape Biomass Project, we are testing the relative significance of site factors on the multifunctional performance of several biomass cropping systems across a topographic gradient. Treatments include five cropping systems—continuous corn, triticale/soy-corn-soy, corn-switchgrass, triticale-sorghum, and triticale-hybrid aspen—randomized, replicated three times across five landscape positions: summit, shoulder, backslope, toeslope, and floodplain. Our objective in this study was to understand how alternative biomass crops affect the distribution of soil moisture across a landscape gradient, with the goal of understanding the potential hydrological impacts of cropping systems within fields and across landscapes. We hypothesized that each treatment would display unique soil moisture patterns over time. To evaluate this, we monitored volumetric water content in 20 cm intervals to a depth of 120 cm during the growing season in 2010, 2011, and 2012, which respectively were wet, average, and drought years.
Our results indicated that mean profile volumetric water content varies significantly among cropping systems and landscape positions over time. Generally, soil moisture was highest at backslope and toeslope positions throughout the growing season, but we also detected unique patterns in soil moisture distribution among cropping systems over time. The continuous corn system usually displayed lower than average soil moisture. We also observed a significant interaction effect between cropping system and landscape position treatments, indicating that some cropping systems are relatively more influenced by landscape position than others. In addition, we determined that total biomass yield and soil-related site factors significantly covary with soil moisture, depending on depth. Our results suggest that, due to differences in relative response to landscape position, the impacts of biomass cropping systems on soil moisture dynamics is heterogeneous in space and time. Our work can be used to help parameterize ecosystem models to predict the water quality and quantity impacts of biomass cropping systems over fields and landscapes.