2002-07-08_GENERAL DOCUMENTS - M2002004 (3)

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8 SMITH, REDENTE, and HOOPER Rather, suitability levels should vary with location and equilibrium level of the organic matter in the surface soil horizon under the proposed post - mining land use. These levels should be such that they supply nutrients to the plant, help ameliorate undersirable soil or site conditions affecting plant growth, and facilitate a self - sustaining soil system. Mined land in the western United States has been reclaimed in recent years largely to one land use: grazing or browsing by livestock and /or wild- life. In a few " "Iocations - mined land has been returned to forest land or cropland. Recognizing that cultivation of rangeland reduces organic matter levels b-y -as much as 50 percent (4), a reduction in organic matter of up to 25 percent from baseline levels in the post-mining soil is a good target for pro- posed post- mining cropland areas. Proposed rangeland areas should be 100 percent of baseline - levels. - Many researchers` believe that the optimum level of organic matter for a mined area is already expressed in the adjacent undisturbed area. But one important consideration is the fact that disturbed systems are in the process of arriving at a balance. As such, adding organic matter may expedite that balance or delay it, depending on the particular set of soil- forming factors in the area. Relationships between baseline conditions and processes of soil organic matter formation. In the surface horizons of undisturbed land, equilibrium organic matter levels generally vary with temperature, rainfall, vegetation cover, soil texture,- physiographic position, and land use management (4). Equilibrium organic matter levels in surface horizons of native soils in min- ing areas of the western United States range from 0.5 to 8 percent (9, 16, 17, 18, 19, 20, 31, 77). In nonmountainous areas of the West organic matter levels range from 0.5 to 3.4, percent and 1 to 6 percent in southern and northern zones, respectively. Organic matter levels in mountainous areas range from 2 to 12.0 percent or higher. Coarser textured soils in the south- eastern United States have a stable fraction level of 1 percent (26). Finer tex- tured soils of the more northern states have a stable fraction level of 3 to 5 percent. At least three organic matter level studies have been done on reclaimed land in the West. At all three sites topsoil salvaging or replacement tech- niques were not used. Organic C levels in a 50- year -old mine soil near Col - strip, Montana, were lower throughout the profile than in adjacent natural soil profiles, except in the upper 5 cm where mine soil organic C levels were higher (68). On 28- to 40- year -old mine soils in Saskatchewan, Canada, humus levels were similar to natural soils (5). In a North Dakota mine soil, organic C levels were lower than those in natural soils (87). In Montana, calculated accumulation rates were about 45.4 gm /yr in a 50- year -old mine soil and about 135 gm/yr in a 10- year -old mine soil that was subjected to heavy fertilization and seeding with vigorous introduced perennial SOIL ORGANIC MATTER grasses and alfalfa (68). Accu calculated in Canada (5). Generally, equilibrium orga cipitation and decrease with organic matter content of soil; eastern Montana, followed it rado, and eastern New Mexic ■ ing equal, organic matter lel and /or silt content. That is, c that in loam, which is greater depositional physiographic pc the upper horizons because runoff received from upslol facilitated by additional mois Equilibrium levels of organi agement. Organic matter level jacent to virgin soils having th ganic matter levels in the virl cultivated soils tend to remair dues and brings them into cor the rate of decomposition" (! In most mining regions of tl ing more common. In these s hinder revegetation efforts a such as low N or P levels, adv particle size class (greater tha sand or clay texture. Even horizons at any given mine immediate adverse effect of k than other undesirable soil cc however, organic matter is pi tinued nutrient cycling relate Mitigating undesirable soil assumption is that ample top ing sites in the West. But "at Moreover, some western min line, or skeletal soils or on st soil. In such areas as the Sa locations in southwestern Wy or nontopsoil material. In so be beneficial. Organic matte capacity of skeletal spoil, bu saline subsoil or spoil, which