Figure 9. Effects of soil texture on concave-shaped areas in the same grower-owned plantation. Top: Silt loam, depth to mottling 36"; middle: silty clay loam, depth to mottling 17"; bottom: silty clay, depth to mottling 7".
Total Soil Depth, Depth to Mottling, and Thickness of the Ap Horizon: Total soil depth can be characterized as being deep, with the average (34 inches) near the maximum of 36 inches for which soil descriptions were made (Table 1), and there were no significant correlations with tree characteristics (Table 2). Average depth to mottling was also relatively deep, 18 inches, with a range of 0 to 36+ inches; of the 80 plots sampled, 27 percent showed no evidence of mottling within the 36-inch depth examined, 18 percent had mottling between 21 and 36 inches, 29 percent between 11 and 20 inches, and 26 percent within the upper 10 inches of the soil. With this preponderance of "moderately wet to wet" soils, there were significant, positive correlations, indicating that all tree characteristics improved as depth to mottling increased (Table 2, Figure 7). However, because of the influence of those "moderately wet to wet" soils, results of the study may not be as reflective of survival, growth, and foliage characteristics of trees growing on well-drained upland sites, particularly those where topographic influences might be stronger.
All study plots showed evidence of an Ap soil horizon, with an average thickness of 7.7 inches and a range from 2 to 10 inches (Table 1); only two tree characteristics, needle length and foliage color, showed significant (positive) correlations with thickness of the Ap horizon, and those were small (Table 2).
Soil Textures: Average soil texture (with percents sand and clay indicated in Table 1) on study plots would be a loam/silt loam for the Ap horizon and clay loam for the B2 horizon. For individual plots, textures ranged from sandy loams to silty clays for the Ap and sandy loams to clays for the B2 horizons; a high proportion of plots had clay percentages in the B2 horizon that would put clay or some combination of clay in the textural designation. This relatively high clay content, coupled with seasonally high water tables and/or concave-shaped surface configurations, is probably largely responsible for the high proportion of plots showing mottling in the soil profile. As shown in Table 2, there were significant correlations between most of the tree characteristics evaluated and soil textures, with individual characteristics being better where sand contents of the Ap and B2 horizons were higher and clay contents lower (Figure 8). As noted earlier, in bottomland areas, the effects of concave-shaped surfaces may not be as detrimental as on coarser-textured soils (Figure 9).
Figure 9. Effects of soil texture on concave-shaped areas in the same grower-owned plantation. Top: Silt loam, depth to mottling 36"; middle: silty clay loam, depth to mottling 17"; bottom: silty clay, depth to mottling 7".