ited on sandy or on loamy sediments. Therefore, it is important to study not only the extent of surface spatial Analysis and interpretation of spatial variability of soils is a keyvariability, but also the distribution of subsurface and stone in site-specific farming. Soil survey maps may have up to 0.41ha inclusions of dissimilar soils within a mapping unit. The objectives deep soil horizons. of this study were to determine the degree of spatial variability of soil Among the various soil physical properties, K s and physical properties and variance structure, and to model the sampling related measures are reported to have the highest statisinterval of alluvial floodplain soils. Soil profiles (n ϭ 209) from 18 tical variability (Biggar and Nielsen, 1976). Bouma parallel transects were sampled with a mean separation distance of (1973) stressed the need for more studies on field vari-79.4 m. Each profile was classified into surface, subsurface, and deep ability of K s and soil water retention curves. Stockton horizons. Structural analysis of soil bulk density (b), sand, clay, satuand Warrick (1971) indicated that variability in K s is rated hydraulic conductivity (K s), volumetric water content (v) at both a function of soil depth and position in the landseven pressure potentials (⌿ a) (Ϫ1, Ϫ10, Ϫ33, Ϫ67, Ϫ100, Ϫ500, and scape, as well as experimental errors in measuring K s. Ϫ1500 kPa) were modeled for the three horizons. Variance of soil Cameron (1978) sampled clay loam soils at six depths physical properties varied from as low as 0.01% (b) to as high as 1542% (K s). The LSD test indicated significant (P Ͻ 0.05) differences from five grid-sampled locations in a 225-m 2 plot. He in sand, clay, b , K s , and v at various ⌿ a. Geostatistical analyses used the desorption method to determine soil water illustrated that the spatially dependent stochastic component was preretention curves at pressure heads ranging from Ϫ10 to dominant over the nugget effect. Structured semivariogram functions Ϫ500 kPa to calculate K s. He found no consistent trend of each variable were used in generating fine-scale kriged contour across sampling depths in pressure head values from maps. Overall autocorrelation, Moran's I, indicated a 400-m sampling Ϫ10 to Ϫ500 kPa, but the shape and magnitude of the range would be adequate for detection of spatial structure of sand, average water retention curve differed among locations. silt, clay, and a 100-m sampling range for soil hydraulic properties He further reported that the coefficient of variation of and b. The magnitude and spatial patterns soil physical property soil water content ranged from 4.3 to 13% in the surface variability have implications for variable rate applications and design layer and from 2.4 to 6.5% in the deeper layers. In a of soil sampling strategies in alluvial floodplain soils. study of spatial variability in soil hydraulic properties, Vieira et al. (1981) used variogram, kriging, and cokriging techniques to determine the magnitude of spatial J. Iqbal, Dep. of Agricultu...
