2002-07-08_GENERAL DOCUMENTS - M2002004 (4)

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Material Topsoil Subsoil Minespoil Figure 3. Schematic diagram illustrating the construction of the subsoil wedge (Step 1) and placement of topsoil over the wedge (Step 2) in the Stanton wedge experiment. Table 6. Average properties of topsoil, subsoil, and mine - spoil in the Stanton wedge experiment (Power et al., 1981). Subsoil Depth 0 inches 4 0.31 12 0.53 20 0.62 28 0.67 36 0.58 48 0.49 60 0.47 72 0.52 SAR EC Clay mmho /cm 1 1 16 6 4 32 25 3 38 tons /acre 0.62 0.63 0.74 0.79 0.88 1.00 0.96 0.95 0.96 0.76 Step 1 0.88 0.94 0.90 0.90 0.85 0.75 Step 2 ° /O Table 7. Average alfalfa yields (1976 -79) as affected by thickness of soil materials at the Stanton wedge experi- ment (Power et al., 1981). Topsoil Depth (inches) Mixed Subsoil - 8 24 topsoil 0.21 0.38 0.58 0.70 0.77 0.82 0.84 0.75 creased from 8 to 24 inches. Maximum yields were obtained when 8 inches of topsoil was placed over 28 inches of subsoil, giving a total soil replacement depth of 36 inches. When topsoil and subsoil were mixed, yields were similar to those obtained with 8 subsoil alone, except at the 36 to 60 Inch thickness es. Yields on the other treatments generally tontine' to decrease at subsoil thicknesses above 28 Inchon When no topsoil was applied, crested whoatgrann yields were highest at subsoil depths of 28 to 36 inches (Table 8) but were always lower than when topsoil was applied. Yields obtained with 8 or 24 inches of topsoil were not different at similar subsoil depths above 20 inches. For subsoil depths below 20 inches, yields tended to be slightly higher (but not significantly) with 24 inches than with 8 inches of topsoil. When topsoil and subsoil were mixed, yields at thicknesses of 20 inches or more were about as high at similar depths of subsoil as when topsoil was applied over subsoil. As with alfalfa, yields tended to decrease at subsoil depths above 28 or 36 inches ex- cept when topsoil and subsoil were mixed. Table 8. Average crested wheatgrass yields (1976-79) as af- fected by thickness of soil materials at the Stanton wedge experiment (Power et al., 1981). Subsoil Topsoil Depth (inches) Depth inches 4 0.67 12 0.86 20 0.90 28 0.98 36 0.92 48 0.80 60 0.78 72 0.70 Mixed Subsoil - 0 8 24 topsoil tons /acre 0.86 0.96 0.99 1.14 1.13 1.08 1.20 1.15 1.13 1.04 1.24 1.27 1.26 1.14 1.16 1.08 0.56 0.91 1.12 1.16 1.20 1.08 1 11 1.20 Highest yields of mixed native grasses (dominated by blue gramma and sideoats gramma) were obtain- ed when topsoil was applied over 20 to 28 Inches of subsoil, with no apparent difference between 8 and 24 inches of topsoil (Table 9). When no topsoil was applied or topsoil and subsoil were mixed, highest yields were obtained at soil depths of 28 to 36 inches, although these yields were lower than on the topsoiled treatments. When topsoil was applied, yields tended to decrease when the subsoil depths were greater than 36 inches. Average wheat yields for 1975 and 1978 were highest when topsoil was applied over 28 to 36 inches of subsoil (Table 10). At each subsoil depth, no yield differences were apparent between 8 and 24 inches of topsoil. When no topsoil was applied, highest yields (but lower than with topsoil) were ob- tained when about 28 inches of subsoil was applied. When topsoil and subsoil were mixed, highest yields (lower than with topsoil) were obtained at the 20 -inch depth. Yields when topsoil was applied tended to re- main the same or decrease slightly when the subsoil depth exceeded 36 inches.