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Soil & Water Management & Conservation

Spatial Characteristics of Claypan Soil Properties in an Agricultural Field

^a Dep. of Soil, Environmental, and Atmospheric Sciences, Univ. of Missouri-Columbia, Columbia, MO 65211
^b USDA-ARS, Cropping Systems and Water Quality Research Unit, Univ. of Missouri-Columbia, Columbia, MO 65211; W.K. Jung, currently at Soil Management Division, National Institute of Agriculture and Technology, 249 Sudun-dong, Suwon-si, Kyunggi-do, Seoul, Korea, 441-707

^* Corresponding author (KitchenN{at}missouri.edu)

Spatial variability in soil properties has long been observed within uniformly managed fields. Understanding the spatial characteristics of soil properties would be helpful in understanding soil–landscape relationships and in the development of site-specific management. The primary objective of this research was to quantify the spatial characteristics of claypan soil properties for a 4-ha agricultural field located in north-central Missouri. Soil samples were collected in 2002 at three depths (0–7.5, 7.5–15, and 15–30 cm) on a 30-m grid. Samples were analyzed for physical, chemical, and microbiological properties. Handheld and mobile apparent soil-profile electrical conductivity (EC_a) values were also obtained. Spatial dependence was not identified for many properties. Yet, at a separation distance of 40 m, clay and silt content, cation exchange capacity, and Bray-1 P were spatially autocorrelated for the 15- to 30-cm depth. Soil EC_a showed a similar spatial autocorrelation. Spatial variations in most soil properties were better estimated by cross-semivariance analysis with EC_a as a secondary variable than by simple semivariance analysis. Clay content was lowest and mostly homogeneous at the 0- to 7.5-cm depth (mean = 170 g kg^–1, SD = 2.0), and highest and most variable at the 15- to 30-cm depth (mean = 410 g kg^–1, SD = 15.8). Thus, the spatial characteristics of soil texture and related soil properties varied greatly by depth and landscape position, probably the result of an uneven distribution of topsoil caused by tillage-accelerated water erosion. We conclude that characterizing the variation in the depth of the claypan horizon is a helpful step in describing other properties for these soils.

Abbreviations: CEC, cation exchange capacity • EC_a, apparent profile electrical conductivity • SOM, soil organic matter • TN, total nitrogen

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