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

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2 COLORADO SCHOOL OF MINES RESEARCH INSTITUTE REVIEW OF LITERATURE Numerous studies have demonstrated the benefits of applying soil during reclamation of mining spoil. Power, Ries, and Sandoval (1976) found a three -fold increase in grass yield and in the rate of water infiltration when only 5 cm of soil was applied to the surface of sodic spoil. Hodder (1973); Farmer et al. (1975); Dusek (1975); McGinnies and Nicholas (1980); and other authors have demonstrated various reclamation benefits when soil is applied to contoured spoil surfaces. In contrast, some research indicates that after 2 to 3 years, produc- tion in spoil is equal to that achieved in soil (Jansen, Dancer, and Dunker, 1981). Other experiments have suggested that plant growth is more dependent on precipitation than on soil depth (Halvorsen, Zimmerman, and Melsted, 1981). While the use of soil in reclamation efforts is well documented, few studies have examined plant growth as a function of soil depth. A number of studies have been conducted by individual mining companies, but the data generated are usually proprietary, and many of these studies lack the controls necessary to integrate them into the published literature. Research conducted by the Northern Great Plains Research Center in Mandan, North Dakota formed a benchmark for soil -depth studies in reclamation situations when "wedge" plots were established in 1974. After leveling sodic (SAR of 25) mining spoil generated at a surface coal mine in central North Dakota, a wedge of subsoil varying in thickness from 0 to 210 cm was applied. Treatments consisted of applying 0, 20, and 60 cm of topsoil (A & B horizons) to the subsoil surface and of mixing topsoil with subsoil. Initial results indicated that the growth and yield of crested wheatgrass and of native grasses increased as soil depth increased to 70 cm; further increases in soil depth had no consistent effect on grass production (Power, Ries, and Sandoval, 1976). Production was greatest when either 20 or 60 cm of topsoil was applied to the subsoil, thus indicating that topsoil should be segregated and applied separately from subsoil in this region. Data collected in subsequent years (Power, Sandoval, and Ries, 1978; Power et al., 1981) confirmed these initial results. In addition, it was found that alfalfa and annual spring wheat required a slightly deeper soil depth to produce maximum yields; yields were near maximum when 70 cm of subsoil and 20 cm of top- soil was returned to the spoil surface. Utilizing the wedge concept to evaluate soil depth requirements for row crops, Jansen, Dancer, and Dunker (1981) found a strong response to soil depth during the first growing season, no response during the second growing season, and a slight response during the third growing season. It was tentatively con- cluded that application of a 6 -in. soil layer over good quality spoil was required to maximize yields of row crops. Several research efforts have utilized soil layers of varying depths rather than a soil wedge to evaluate soil -depth requirements. For example, investiga- ting reclamation of slightly sodic spoil in North Dakota, soil layers of 5, 15, 30, and 60 cm were applied to spoil. Maximum yield of annual crops was found at a soil depth of 30 cm (Halvorsen, Zimmerman, and Melsted, 1981). Working in western Colorado, McGinnies and Nicholas (1980) found that both aboveground and belowground biomass increased as soil depth over spoil increased from 0 to 46 cm (the maximum depth tested). Over a 3 -year period, Schuman, Rauzi, and Taylor (1980) found that native grass production increased as soil thickness increased to the 61 -cm soil depth, the maximum depth tested at the Wyoming site. In a later study, Schuman and Power (1981) recommended that depth of topsoil applied 1 • 1 1 1 1 1 1 1 1 1 1 1 1 1 1