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

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k inch of minerals The water - holding capacity is dependent upon these properties. INITIAL EXPERIMENTS COMPARING TOPSOIL WITH CHEMICAL AMENDMENTS AND STRAW MULCH When the first reclamation law was passed in North Dakota in 1970, initial efforts were focused on the reestablishment of vegetation on reshaped spoils. Sandoval et al. (1973) noted that the severity of revegetation problems increased as the clay con- tent and exchangeable sodium percentage (ESP) of the spoils increased. They observed that while spoil properties varied widely within and between mine areas, the severity of the problems associated with high clay and high sodium contents also tended to increase with overburden depth at each site. The earliest work on vegetative reestablishment in North Dakota compared replacement of topsoil with applications of chemical amendments and straw mulch (Sandoval et al., 1973; Power et al., 1974; and Power et al., 1975). Typical results from one experi- ment are given in Table 1; the spoil at this location has an ESP of about 25. These results indicate that while gypsum applied to sodic spoil increased pro- duction, much higher yields were obtained when 2 inches of topsoil was applied. Straw mulching in- creased vegetative production both on topsoiled and nontopsoiled plots. Table 1. Slender wheatgrass yields as affected by chemical amendments, straw mulch, and topsoil application on highly sodic spoil (Power et al., 1974). Amendment No straw Straw No straw Straw None Gypsum Sulfur 0 227 47 Dry matter yield No topsoil Two inches topsoil pounds /acre 63 605 316 921 62 930 1283 746 1587 Identical experiments were initiated in 1973 at four mine sites (Merrill et al., 1983b) in which each of two topsoil applications (none or 12 inches) was combined with each of two gypsum treatments (none or 10 tons per acre). On topsoil treatments, gypsum was incorporated into the spoil prior to ap- plication of topsoil. Crested wheatgrass was seeded on all except selected plots which were summerfal- lowed for three years before seeding. The purpose of summerfallowing was to increase moisture content in the soil and spoil and promote the downward leaching of sodium displaced by calcium from ap- plied gypsum. Summerfallowing proved ineffective in increasing gypsum effectiveness. Average yields 5 `or the four -year period 1975 -78 and yields for 1983 are given in Table 2. At the highly sodic Zap site, average yields from 1975 to 1978 without topsoil were Tess than half of yields when topsoil was ap- plied. Gypsum had little effect on yields at Zap on either the no topsoil or topsoiled treatments. On the moderately sodic Beulah and Stanton sites, gypsum did not affect yields on the topsoil plots in the 1975 -78 period; however, when gypsum was applied to the plots which were not topsoiled, yields ap- proached those on the topsoiled plots. On the non - sodic Center site, average yields from 1975 -78 were not affected by gypsum, but yields tended to be higher when topsoil was applied. In 1983, yields at each location were much lower than yields for the 1975 -78 period, partly because of climatic and stand differences and partly because nitrogen fertilizer was not applied after 1978. No consistent yield dif- ferences due to gypsum were apparent in 1983 at any site except possibly at Stanton. However, 1983 yields obtained 10 years after topsoil was applied tended to be two or three times as large as when no topsoil was applied. These results emphasize the need for respreading topsoil, since neither stands or yields were maintained when only gypsum was ap- plied. Table 2. Average crested wheatgrass yields from 1975.78 and yields for 1983 at four mines as affected by topsoil and gypsum. SAR of Mine Spoil Center Beulah Stanton Zap 1 1975 -78 1983 11 1975 -78 1983 12 1975 -78 1983 27 1975 -78 1983 Average No topsoil Topsoil' relative No No yield Year Gypsum Gypsum' Gypsum Gypsum' w/o topsoil 1.6 04 09 03 09 0.1 0.4 1.3 0.2 1.1 0.3 1.1 0.2 0.3 tons /acre 1.7 07 11 0.6 11 05 07 0.6 1.8 0.8 1.1 0.6 1.2 0.7 08 0.8 '12 inches of topsoil applied 10 tons per acre of gypsum applied to spoil before topsoiling no yields obtained due to loss of stand 84 37 90 55 84 27 47 These initial experiments demonstrated that top- soil depths needed for optimum yields would be related to the quality of the underlying spoil, with greater depths of good quality soil needed to restore productivity on poor quality spoil. This is illustrated by results given in Figure 1 from treatments without gypsum as reported by Merrill et al. (1981). On ade- quately fertilized plots on nonsodic spoil, yields were 8 percent higher on topsoiied plots than on nontopsoiled plots, 29 percent higher on moderately sodic spoil and 84 percent higher on highly sodic spoil. The lower yields obtained with topsoil as the sodicity level in the spoils increased indicated that 12 inches of topsoil was not enough to restore op- timum productivity. Doering and Willis (1975) conducted a laboratory and field study of chemical reclamation for highly sodic strip -mine spoil (SAR 25) using gypsum and