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

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Yield increase due to topsoil ( %) 8 1.5- m 1.0- 1 c c 0.5- 0 (] no topsoil topsoil 25 33 84 11 12 27 SAR of Spoil Figure 1. Yields of crested wheatgrass with and without 12 inches of topsoil at four sites with different SAR values (Merrill et al., 1981). calcium chloride. Gypsum, because of its low solubility, was not an effective reclamation agent. Calcium chloride (0.25 Molar) was sufficiently solu- ble to increase the hydraulic conductivity of the spoil so that the replaced sodium was leached down- ward. Their results indicated that chemical reclama- tion of sodic spoils was feasible but not practical due to the high cost of calcium chloride. Their results and the results of other North Dakota ex- periments led Merrill et al. (1981) to conclude that the use of chemical amendments was feasible only when an adequate supply of suitable plant growth material is not available. TOPSOIL DEPTH EXPERIMENTS Since the earlier experiments indicated that 1 foot of soil replacement was inadequate to restore premine productivity, further research was con- ducted to compare the effects of different soil depths. Yield and Establishment of Forage Grasses: The first experiment in North Dakota comparing different depths of topsoil was initiated in 1972 at Stanton (Ries et al., 1978). The spoil at this site was highly dispersed (SAR 25) and moderately high in clay (silty clay loam). Topsoil was applied at depths of 0, 2, 6, and 12 inches. Two fertilizer treatments were applied at each topsoil depth - no fertilizer or fertilized with 100 pounds per acre of phosphate in- itially (and none thereafter) plus 50 pounds per acre of nitrogen each year for the first three years (and none thereafter). The experiment was conducted for nine years, but yields were obtained only the first three and the last two years. Yield trends for crested wheatgrass and native grasses were similar, so only crested wheatgrass yields are given (Table 3). 6 Table 3. Yields of crested wheatgrass in selected years from 1974 to 1982 with (w) and without (wlo) fertilizer as affected by topsoil depth (Ries, et al., 1978 and unpublished USDA/ARS data). Yield Topsoil 1974 1975 1976 1981 1982 depth w wlo w wlo w w/o w wlo w w/o inches 0 2 6 12 0 0 1.8 0.4 1.7 0.6 2.0 1.1 -- 0.1 1.1 0.6 0.6 1.2 0.8 0.7 1.7 1.3 0.8 tons /acre 0 0.1 0.4 0.4 0.4 0.5 0.7 0.6 0 0.3 0.4 0.6 0 0.7 0.8 1.0 0 0.4 0.6 0.9 Each year, yields were higher when 12 inches of topsoil was applied, but the rate of yield increase in- dicates that maximum yields were not attained at the 12 -inch depth even with adequate fertilization. The application of fertilizer increased yields at each top- soil depth every year. The persistence of this in- crease through the ninth year suggests that part of this fertilizer increase was due to phosphorus ap- plication, but the relatively greater increases in the first three years indicate that yields were also in- creased by nitrogen fertilizer. The relative response to fertilizer decreased as the depth of topsoil was in- creased; this decrease can be attributed to the available nutrient content of the replaced topsoil. These results also suggest that the optimum depth of soil replacement is not reduced by fertilization. The effect of topsoil thickness on stand establish- ment (plants per unit area, not yield) was measured in 1974 and 1976, two and four years after crested wheatgrass was seeded. When no topsoil was ap- plied, stands were much lower than when topsoil was applied (Figure 2), but stands did not increase as the depth of soil increased. Since these measure- ments were made in 1974 and 1976, they do not reflect any long -term effects of topsoil thickness upon stand retention. Stands were subsequently observed to decline even further on plots to which no topsoil was applied. 80 - 60 - 40 - 20 0 0 2 6 12 Topsoil depth (Inches) Figure 2. Effect of topsoil depth over sodic minespoil on stand density of crested wheatgrass (Ries et al., 1978).