Modeling spatial variability and transport processes in a glacial till soil

The objective of this study was to investigate the spatial variability of different physical and chemical properties of soils, and their role on transport processes of chemicals to groundwater sources in a glacial till soil of central Iowa;Measurements were made to determine the in-situ saturated hydraulic conductivity (K[subscript] sat) of a glacial till soil at sixty six sites in a tillage established plot. One hundred thirty-two data points on K[subscript] sat collected at two soil depths along two bisecting perpendicular transects, were used to develop semivariogram models, in conjunction with split-window median polish approach. Nested structure with an overall range of 60 m was found for the K[subscript] sat at a depth of 30 cm below the soil surface. K[subscript] sat values at 15 cm depth were found as structureless random noise;Another data set was collected on nitrate-nitrogen (NO[subscript]3-N) concentration in soil water, soil moisture content, and soil profile NO[subscript]3-N content in the same field under two different tillage practices using a different sampling pattern. Data on NO[subscript]3-N concentration in the soil water collected at 175 grid points arranged on a three dimensional (3-D) grid, were compared for spatial distribution patterns as function of the tillage system. Results of this study indicated transitional spatial structure of NO[subscript]3-N distribution, both in vertical and horizontal directions, under conventional tillage. In contrast, nugget and linear type semivariograms were observed for the no tillage system, in the vertical and horizontal directions, respectively;Data on soil moisture content, NO[subscript]3-N concentration in soil water, and soil total NO[subscript]3-N contents in the soil profile collected at five soil depths (30, 60, 90, 120, and 150 cm below the ground surface) in a tile drained plot were studied for coregionalization. This study indicated that well-structured cross semivariograms existed between depths of 60 and 90 cm, and 90 and 120 cm, for NO[subscript]3-N concentration and soil moisture content. Strong negative correlation between soil moisture content and NO[subscript]3-N concentration resulted in negative cross-semivariograms at 90 and 120 cm depths;A deterministic simulation model was developed with an effective hydraulic conductivity parameter based on the spatial correlation length in place of an average hydraulic conductivity parameter, to simulate the major water and nitrate transport processes for predicting the NO[subscript]3-N losses to subsurface drainage systems. (Abstract shortened by UMI.