Soil spatial variability relationships in a steeply sloping acid soil environment

Management of pastures in steep terrain can be expensive in terms of time, chemical inputs, and equipment requirements. Management of those portions of pasture that will yield the most for minimum inputs requires a knowledge of the spatial patterns of the soil and atmospheric environments. A steep 2.4-ha unimproved pasture in southern West Virginia was studied to determine the spatial dependency of aboveground biomass production on soil characteristics. The predominant soil of the study site was Gilpin silt loam (fine-loamy, mixed, mesic, Typic Hapludults) with an average A-horizon pH (1:1 H2O) of 4.5 (range 3.8 to 6.1). The study site was broadcast seeded with red fescue (Festuca rubra L.) in 1982, making it the major plant species. However, several other plant species, including orchardgrass (Dactylis glomerata L.), red clover (Trifolium pratense L.), white clover (Trifolium repens L.), broomsedge (Adropogon virginicus L.), velvet grass (Holcus lanatus L.), yarrow (Achillea millefolium L.), and wild strawberry (Fragaria virginiana L.), and others were common. Transects were laid out up and down the north-facing, south-facing, and west-facing slopes and one transect was established on the contour for measurement of soil characteristics at a 1-m spacing. Plant aboveground biomass was measured at a 2-m spacing on three of the slope transects and on the contour transect. Although correlation analysis failed to find many statistically significant relationships between biomass production and soil characteristics, cross-semivariogram analyses of biomass production and surface soil pH and extractable Al, Mn, and P indicated that a strong spatial dependency exists. Those relationships were used for identifying homogeneous areas of biomass production and associated soil characteristics by ordinary kriging.