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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

View larger version (33K): [in a new window]   Fig. 1. Research site and sampling design (dotted lines represent sampling transects E and H, which were selected to illustrate topsoil variation in Fig. 9).

View larger version (30K): [in a new window]   Fig. 2. Frequency distributions of soil properties by soil depth. Soil ECa (apparent profile electrical conductivity) was measured using two methods and aggregate stability was only measured for the surface depth at each location. CEC = cation exchange capacity; SOC = soil organic carbon.

View larger version (19K): [in a new window]   Fig. 3. Relationship between handheld and mobile ECa (apparent profile electrical conductivity) readings.

View larger version (28K): [in a new window]   Fig. 4. Spatial autocorrelation (Moran's I) of soil physical and chemical properties by soil sampling depth. CEC = cation exchange capacity; SOC = soil organic carbon; TN = total nitrogen.

View larger version (20K): [in a new window]   Fig. 5. Spatial autocorrelation (Moran's I) of (a) microbiological soil properties and aggregate stability for the 0- to 7.5-cm depth, and (b) soil ECa (apparent profile electrical conductivity).

View larger version (31K): [in a new window]   Fig. 6. Interpolated maps of 15- to 30-cm CEC (cation exchange capacity) obtained by kriging and by cokriging with handheld ECa (apparent profile electrical conductivity) and mobile ECa as a covariate. Mapped area is the same as that shown in Fig. 1.

View larger version (27K): [in a new window]   Fig. 7. Interpolated clay content maps for each sampling depth using cokriging with handheld soil ECa (apparent profile electrical conductivity; n = 55) as a covariate. Mapped area is the same as that shown in Fig. 1.

View larger version (20K): [in a new window]   Fig. 8. Semivariograms and kriged maps of handheld and mobile ECa (apparent profile electrical conductivity). Mapped area is the same as that shown in Fig. 1.

View larger version (23K): [in a new window]   Fig. 9. Elevation of the soil surface, elevation of the bottom of the three sampling depths (dashed lines), and elevation of the top of the argillic horizon for two east–west transects (see transect locations on Fig. 1). This illustrates how a given sampling depth may either include or exclude a portion of the argillic horizon, depending on position in the landscape.