Spatial Variability and Scaling of Infiltration on Undulating Agricultural Terrain.
Timothy Green1, Lajpat Ahuja1, G.H. Dunn2, J.C. Ascough2, Gregory S. McMaster2, L. Ma2, R.H. Erskine2, J.D. Salas3, D.B. Palic2, M.R. Murphy2, and M.W. Strudley2. (1) USDA-ARS, USDA-ARS Agricultural Systems Res., 2150-D Centre Ave #200, Fort Collins, CO 80526-8116, (2) Agricultural Systems Research Unit, USDA-ARS, 2150-D Centre Ave #200, Fort Collins, CO 80526-8116, (3) Civil Engineering, Colorado State U., Fort Collins, CO 80526
This presentation focuses on surface water infiltration and soil physical properties affecting spatial soil water, nutrient, and plant estimation along with uncertainty and scaling associated with spatial variability. The field site in northeastern Colorado, USA comprises undulating agricultural terrain cropped with winter wheat under conventional tillage. We illustrate potential complexities encountered in the field concerning spatial variability of infiltration rates and associated soil properties. Our field experiments include 150 sorptivity and steady infiltration measurements followed by gravimetric sampling of soil water contents at two depths (48 hours after drainage) taken at ten landscape positions. At each landscape position, dry sorptivity and steady infiltration were measured using fifteen 0.30-m diameter rings distributed randomly in nested patterns within an area of 30-m by 30-m. Soil hydraulic properties were also estimated from soil core data using similar media concepts and functional normalization. Data were analyzed for spatial scaling behavior by fitting power-law variograms and estimating a Hurst coefficient at each landscape position and at different scales across the field. In addition to quantifying the observed spatial variability in soils and infiltration rates, inferences will be made for scaling up measurements. Furthermore, process-based modeling of infiltration and its scaling behavior under different soil scaling in space will be discussed. These results are intended to shed new light on research needed to address spatial variability of soils and interactions between land areas when modeling infiltration, runoff, and plant water use under different climates and land management strategies.