SPATIAL DEPENDENCE AND RELATIONSHIPS OF ELECTRICAL CONDUCTIVITY TO SOIL ORGANIC MATTER, PHOSPHORUS, AND POTASSIUM.

Apparent electrical conductivity (ECa) can be an indirect indicator of soil nutrient concentrations, and strong relationships between ECa and nutrients may help delineate fertility management zones. The objectives of this study were to determine the relationships among ECa, organic matter (OM), P, and K and to assess the spatial dependency and correlation components of such relationships. Spatial correlations and relationships of ECa with OM, P, and K were determined using geostatistical and regression analyses. ECa was measured in parallel transects 4.6 m apart in adjacent Indiana (United States) fields with multiple soil series in 2001, 2002, and 2003. Electrical conductivity, OM, P and K were strongly spatially dependent. Spatial correlations between ECa and these variables were cyclic: positive at distances of <40 m, but negative at distances <70 m. Organic matter, P, and K showed relatively low but significant correlations with ECa in all the 3 years of study. Maximum correlations were obtained with OM, P, and K (r = 0.55, 0.50, 0.53, respectively) when soil moisture content was relatively higher in 2003. Data separation by soil series improved correlations between ECa and soil chemical attributes when the soil was a Mollisol, but not for an Alfisol. Regression models showed that ECa was significantly related to the variables but that ECa failed to detect concentration changes and explained <7% of the variability of these nutrients. The results suggested that ECa has limited usefulness in estimating soil chemical properties or in defining possible management zones for OM, P, and K in these soils.