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ARS Home » Midwest Area » Columbia, Missouri » Cropping Systems and Water Quality Research » Research » Publications at this Location » Publication #184494

Title: SPATIAL CHARACTERISTICS OF CLAYPAN SOIL PROPERTIES IN AN AGRICULTURAL FIELD

Author
item JUNG, WONKYO
item Kitchen, Newell
item Sudduth, Kenneth - Ken
item ANDERSON, S

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/17/2006
Publication Date: 6/21/2006
Citation: Jung, W., Kitchen, N.R., Sudduth, K.A., Anderson, S.H. 2006. Spatial characteristics of claypan soil properties in an agricultural field. Soil Science Society of America Journal. 70(4):1387-1397.

Interpretive Summary: About 10 million acres of claypan soils are found in the U.S. Midwest. The sub-surface claypan of these soils causes them to have very slow water infiltration, particularly during the winter and spring. Because of this characteristic, tillage for grain crop production causes these soil landscapes to be especially vulnerable to surface runoff and erosion. With erosion, many chemical, physical, and biological properties of these soils are also negatively altered. However, since erosion is not uniform, the impact on soil properties is not likely to be the same in all areas within a field, even when the field is uniformly managed. The purpose of this research was to investigate how a select group of these properties, often called soil quality indicators, vary relative to their location within crop production fields. We found that accurate maps could not be created for many of the chemical and biological properties, even when sample locations were only 60 feet apart. However, spatial trends were evident for many physical properties, such as clay and silt content and cation exchange capacity. So for these properties if sample locations were not separated by more than about 120 feet, the information could be used to create accurate maps. Yet this still means that mapping soil quality properties on these soils requires taking soil samples from many locations within each acre. Time and soil analysis costs prohibit farmers from investing in this type of intense sampling for production-scale agriculture. However, we also found that by using a soil sensor that can quickly measure soil electrical conductivity in the field and does not require soil sampling and lab analysis, we could do a better job of estimating field variation in some soil properties, particularly some physical properties. We also found that an uneven distribution of topsoil depth above the claypan was the landscape feature most related to the soil quality properties. We conclude that characterizing the variation in the depth of the topsoil is a critical step in understanding quality of these soils. Knowing how soil quality properties change within fields could help farmers know how and where to target soil sampling or obtain other sensor measurements. Characterizing important soil quality parameters and how they change within fields will provide a basis for considering management strategies helpful in developing sustainable food and fiber production systems.

Technical Abstract: Spatial variability in soil properties has long been observed within uniformly–managed fields. Understanding the spatial characteristics of soil quality properties may help in the formulation of site–specific management plans. The primary objective of this study was to quantify the spatial characteristics of soil properties for a field with claypan soils. Soil samples were collected in 2002 at three depths (0 to 7.5, 7.5 to 15, and 15 to 30 cm) on a 30–m grid within a 4–ha agricultural field located in north central Missouri. Samples were analyzed for physical, chemical, and microbiological properties that serve as soil quality indicators. Hand-held and mobile apparent soil-profile electrical conductivity (ECa) values were obtained at the same locations. Evidence of spatial dependence was lacking for many soil properties. Yet, at a separation distance about 40 m, clay content, silt content, CEC, and Bray1-P were spatially autocorrelated for samples taken from the 15- to 30-cm depth. Soil ECa showed a similar spatial autocorrelation. Spatial characteristics of most soil properties were better estimated by cross-semivariance analysis with ECa as a secondary variable than by simple semivariance analysis. Clay content was lowest and mostly homogeneous at the 0- to 7.5-cm soil depth (mean=170 g/kg, SD=2.0), and highest and most variable at the 15- to 30-cm soil depth (mean=410 g/kg, SD=15.8). Thus, the spatial characteristics of soil texture and other related soil properties varied greatly by soil depth and landscape position, likely the result of an uneven distribution of topsoil depth caused by tillage-induced erosion. Sensor–based ECa measurements improved accuracy when characterizing spatial variation in soil quality properties. We conclude that characterizing the variation in the claypan horizon, especially the depth of topsoil above the claypan, is a critical step in understanding soil quality of these soils.