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

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Table 17. Yield of wheat in 1982 and corn silage in 1983 under irrigation at Falkirk trench plots as affected by thickness of soil replacement and overburden material. Topsoil Thickness inches 9 18 27 9 18 27 Overburden Material Overburden Material Gravelly loamy sand Clay loam No Subsoil Subsoil 22.5 25.6 26.1 11.5 13.7 15.5 Most of the differences in yield between the dif- ferent overburden materials appear to be related to their water - holding capacity. Total water content of the top 5 feet of each treatment was determined at planting and harvest from 1979 through 1982, and averages for all topsoil thicknesses of each treat- ment are given in Table 18. The data refer to total water content, not to available water; the water con- tent of the silty clay loam overburden at the perma- nent wilting percentage is nearly three times as high as that of the gravelly loamy sand (Table 15). How- ever, soil water depletion from planting to harvest is indicative of the water - supplying capacity of the dif- ferent overburden materials. When average yields for all soil thicknesses for each treatment are com- pared, yields tended to increase as water depletion increased from 1.5 to 1.8 inches but did not increase when depletion increased from 1.8 to 2.3 inches. The data obtained do not adequately explain why the greater water depletion on the silty clay loam treat- ments is not reflected by increased yields. The in- crease in soil water from harvest to planting the next spring is also indicative of the capacity of these materials to retain nongrowing season moisture for crop use. Table 18. Average moisture levels in the top 5 feet of the Falkirk trench plots at planting and at harvest from 1979 to 1982 averaged for all topsoil thicknesses. Gravelly loamy sand Gravelly loamy sand plus subsoil Clay loam Silty clay loam Wheat bushels /acre 30.0 32.4 33.7 32.0 35.7 33.0 Com Silage tons /acre - 18.6 16.9 19.1 18.8 18.5 19.3 Water Content silty clay loam 30.9 36.1 30.4 17.1 19.5 17.5 Planting Harvest Depletion 10.8 9.2 1.6 13.9 15.8 17.2 inches /five feet 12.1 14.1 14.8 1.8 1.7 2.4 These results indicate that replacement of topsoil is required for restoration of optimum yield levels. Yields with 9 inches of topsoil were lower than those 14 with 18 or 27 inches of topsoil, while yields with 27 inches tended to be slightly higher than with 18 in- ches. Lowest yields were obtained with gravelly loamy sand overburden, but when subsoil was add- ed, yields tended to be equivalent to those when overburden was clay loam or silty clay loam. On the clay loam, silty clay loam, and gravelly sandy loam with subsoil treatments, optimum yields were ob- tained with 18 to 27 inches of topsoil and were equal or better than on the undisturbed plots. When 27 inches of topsoil was placed over gravelly loamy sand, yields were about 84 percent of maximum yields on the other treatments without irrigation and about 78 percent of those when irrigated. By inter- polation, this would suggest that soil materials of medium to fine texture should be replaced to a total thickness of at least 32 to 36 inches for restoration of optimum productivity when the overburden is coarse - textured. COMPARISONS OF YIELDS FROM RECLAIMED AND UNDISTURBED SOILS An experiment was conducted from 1980 through 1982 to compare yields from undisturbed and reclaimed soils. Three experimental sites were selected at each of two locations, one near the Knife River Mine at Beulah and the other near the Baukol- Noonan Mine at Center. At each location, one site was located on an undisturbed prime soil, one on an adjacent undisturbed nonprime soil, and the third on a newly reclaimed soil. Prime and nonprime soils were classified by the criteria established by the Soil Conservation Service of the United States Depart- ment of Agriculture. The prime site at Beulah was Grail clay loam; the top 8 feet of the profile was clay loam in texture, and the 8 to 10 -foot depth was loam. The nonprime site was Max loam; the top foot was loam in texture, from 1 to 8 feet was clay loam, and the 8 to 10 -foot depth was clay. The nonprime site was located approx- imately 300 feet from the prime site; both sites were about four miles southeast of the Knife River Mine. The reclaimed area (within the Knife River Mine) was reshaped and respread with one foot of topsoil over slightly sodic spoil (SAR 5) in the spring of 1980; the texture of the topsoil was clay loam and that of the spoil was clay. The prime site at Center was Arnegard loam; the texture to the 10 -foot depth was loam. The nonprime soil was Parshall sandy loam; the top 3 feet and the 7 to 10 -foot depth were sandy loam, with a loamy sand layer between 3 and 7 feet. The sites were located about 200 feet apart and were one mile from the Baukol- Noonan Mine. The reclaimed site in the Center mine was reshaped and respread with 2 feet of subsoil and 1 foot of topsoil over nonsodic spoil in the spring of 1980. The topsoil and subsoil were