Spatial Variability Analysis of Soil Physical Properties of Alluvial Soils

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, Ks 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 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 vari79.4 m. Each profile was classified into surface, subsurface, and deep ability of Ks and soil water retention curves. Stockton horizons. Structural analysis of soil bulk density ( b), sand, clay, satuand Warrick (1971) indicated that variability in Ks is rated hydraulic conductivity (Ks), volumetric water content ( v) at both a function of soil depth and position in the landseven pressure potentials ( a) ( 1, 10, 33, 67, 100, 500, and scape, as well as experimental errors in measuring Ks. 1500 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% (Ks). The LSD test indicated significant (P 0.05) differences from five grid-sampled locations in a 225-m2 plot. He in sand, clay, b, Ks, 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 10 to dominant over the nugget effect. Structured semivariogram functions 500 kPa to calculate Ks. 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 10 to 500 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 S variability of soil physical properties within variation and reported a range of 50 m for 1280 field or among agricultural fields is inherent in nature measured infiltration rates. Vauclin et al. (1983) samdue to geologic and pedologic soil forming factors, but pled within a 70by 40-m area at the nodes of a 10-m some of the variability may be induced by tillage and square grid and used classical and geostatistical techother management practices. These factors interact with niques to study spatial variability of sand, silt, and clay each other across spatial and temporal scales, and are contents, available water content (AWC), and water further modified locally by erosion and deposition stored at 33 kPa. The strongest correlation was found processes. Soils in the Mississippi Delta are alluvial in between sand content and AWC (r 0.83) and the nature, originating from different soils, rocks, and uncross variogram demonstrated that sand content was consolidated sediments in 24 states from Montana to spatially correlated with soil water content at 33 kPa Pennsylvania, and deposited by the Mississippi and Ohio within a distance of ≈30 m and with AWC within a Rivers and their tributaries (Logan, 1916). The stratifidistance of ≈43 m. Sobieraj et al. (2003) found no spatial cation of different sediments deposited on top of each structure in Ks at distances 25 m. Heiskanen and other spatially vary, for example, sandy sediments on Makitalo (2002) reported a range of 44 and 100 m for top of clays or at other locations clay sediments deposthe water content and air-filled porosity at a 10 kPa. Campbell (1978) reported sand content semivarioJ. Iqbal, Dep. of Agricultural and Biological Engineering, and F.D. gram ranges of 30 and 40 m for two different soil types. Whisler, Dep. of Plant and Soil Sci., Mississippi State Univ., and J.N. In summary, it is evident from the above studies that Jenkins, USDA-ARS, Crop Science Research Lab., P.O. Box 5367, Mississippi State, MS 39762; J.A. Thomasson, Dep. of Agricultural spatial variability of various soil physical properties are and Biological Engineering, Texas A&M University, College Station, scale-dependent, especially the water transport properTX 77843; P.R. Owens, Dep. of Agronomy, Lilly Hall of Life Sci., ties of soils; therefore, it is a prerequisite to quantify the 915 W. State Street, Purdue Univ., West Lafayette, IN 47907. This spatial variability of soils before designing site-specific study was in part supported by The National Aeronautical and Space applications like variable rate irrigation (VRI), seed Administration funded Remote Sensing Technology Center at Mississippi State University. Received 3 May 2004. *Corresponding author rate, fertilizer rate, and strategies for future soil sam([email protected]). pling, especially for alluvial floodplain soils. The objecPublished in Soil Sci. Soc. Am. J. 69: – (2005). Soil & Water Management & Conservation Abbreviations: v, volumetric water content; b, soil bulk density; a, pressure potential; AWC, available water content; FC, field capacity; doi:10.2136/sssaj2004.0154 © Soil Science Society of America Ks, saturated hydraulic conductivity; OM, organic matter; VRI, variable rate irrigation; WP, wilting point. 677 S. Segoe Rd., Madison, WI 53711 USA