A survey of soil attributes in North Dakota by landscape position

Land surveys of soil attributes can provide valuable information on the geographic distribution of important soil attributes and summarize the levels found. Landscape position can have a major influence on soil attributes. Consideration of field landscape variables in selecting sampling locations and interpreting results, even in large-scale surveys, should help to reduce unexplained variability in many soil attributes. We report the results of a survey of selected soil attributes in agricultural fields across North Dakota at sites selected within each field by landscape position. Our objective was to determine if this sampling design might contribute to a better understanding of the distribution of soil attributes. Soils from two or three fields within each of the 53 counties of North Dakota were sampled in 1996. Within each field, three samples of surface soil (0-15 cm) were obtained. One sample was collected from an upland position, one from a slope, and one from a depression. Each field was georeferenced using a differentially corrected GPS receiver. The samples were analyzed for DTPA (diethylenetriaminepentaacetic acid)-extractable Cu, Zn, and Cd; water soluble B and Se; and soil pH. Mapping and analysis showed distinct regional patterns of all soil factors. Some soil attributes, including pH and extractable Zn, Cu, and Cd, exhibited a strong relationship to field landscape position, while soluble B and Se were less related. The results suggest that separating field sampling locations into upland, sloping, and depressional areas will reduce the confounding effects of field landscape position on larger-scale spatial trends in soil attributes.