Fig. 3. Sample variograms for 1990 (DeBusk et al., 1994) and 1998 Water Conservation Area 2A (WCA-2A) soil total P data sets. Both variograms were fit to a spherical model; parameter values are indicated on graphs (A₀ = range, in km, of spatial autocorrelation for total P; C₀ + C = sill, or maximum semivariance; C₀ = nugget semivariance).