Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 2, 2014
Publication Date: N/A
Interpretive Summary: Surface and subsurface redistribution of soil water sharply influences plant growth, crop productivity, and water quality. Measuring variations in these soil-water conducting processes are key components in modeling watershed responses to natural inputs and the impacts of soil-plant-water management activities. This study discovered that extensive reworking of hillslope soils by shallow-rooted grasses decreased water-conducting variations across different land uses and soil types. This finding suggests that fewer measurements are required from landscape positions and soil series in grassland-based agroecosystems. Results will be highly beneficial for watershed-scale modelers evaluating impacts in the region.
Technical Abstract: Heterogeneity of infiltration and subsurface redistribution of soil water can have a profound influence on plant growth and productivity as well as water quality. However, substantial uncertainty exists in assessing hydrologic impacts over multiple scales with complexity potentially compounded by multiple, adjacent land uses. Spatial and temporal variability of surface soil hydraulic properties are key elements in understanding and modeling vadose zone hydrodynamics, and site-specific parameterization is necessary for effective watershed management due to the interactive effects of hydrology, ecology, and human activities at local to regional scales. The objective of this investigation was to evaluate the effects of land use, soil series, and topographic position on surface soil physical, biogeochemical and hydraulic properties, namely ponded and tension infiltration as well as hydraulic conductivity, during a period of shallow aquifer recharge. Measurements were made across three Fragiudults (Captina, Nixa, and Johnsburg soil series) on a relatively young, alley-cropped agroforestry tract and an adjacent cattle-grazed pasture that comprise a headwater hillslope soil assemblage in the Ozark Highlands. Double-ring and tension infiltrometer methods were used to quantify surface soil hydraulic properties. Slight variations in ponded and/or tension infiltration occurred among land uses, soils, and topographic positions for individual measurements. However, when all individual infiltration measurements were pooled together and evaluated, a single infiltration-pressure head function characterized the entire hillslope soil assemblage during the transition from Fall to Winter when shallow aquifer recharge is occurring. Extensive bioturbation in upland forage-covered settings may serve to naturally dampen hydraulic property variability across soils, which may simplify rather than complicate hydrologic partitioning between infiltration and run-off in grassland-based agroecosystems receiving frequent applications of animal manures in the Ozark Highlands.