FIELD-SCALE VARIABILITY OF SOIL PROPERTIES IN CENTRAL IOWA SOILS

Spatial distributions of soil properties at the field and watershed sc ale may affect yield potential, hydrologic responses, and transport of herbicides and NO3- to surface or groundwater. Our research describes field-scale distributions and spatial trends for 28 different soil pa rameters at two sites within a watershed in central Iowa. Two of 27 pa rameters measured at one site and 10 of 14 parameters measured at the second site were normally distributed. Spatial variability was investi gated using semivariograms and the ratio of nugget to total semivarian ce, expressed as a percentage, was used to classify spatial dependence . A ratio of <25% indicated strong spatial dependence, between 25 and 75% indicated moderate spatial dependence, and >75% indicated weak spa tial dependence. Twelve parameters at Site one, including organic C, t otal N, pH, and macroaggregation, and four parameters at Site two, inc luding organic C and total N, were strongly spatially dependent. Six p arameters at Site one, including biomass C and N, bulk density, and de nitrification, and 9 parameters at Site two, including biomass C and N and bulk density, were moderately spatially dependent. Three paramete rs at Site one, including NO3- N and ergosterol, and one parameter at Site two, mineral-associated N, were weakly spatially dependent. Distr ibutions of exchangeable Ca and Mg at Site one were not spatially depe ndent. Spatial distributions for some soil properties were similar for both field sites. We will be able to exploit these similarities to im prove our ability to extrapolate information taken from one field to o ther fields within similar landscapes.