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

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204 OPER t /ha, compared to 32 t /ha on bare rt #cats Yado no topsoil loss was observed on reclain ea, iOE percent sropes (loamy texture) with 3.36 t /ha of crimped -in straw (63). In summary, organic matter applied and incorporated or in -situ reduces erosion. Erosion rates on bare topsoil with high organic matter levels are 25 to 75 percent lower than on bare soils with low organic matter levels. Ap- plications of straw mulch in excess of about 3.0 t /ha probably will reduce erosion to barely measurable levels. Climate. In the mining areas of the arid and semiarid West annual precipitation ranges from 15 to 46 cm. While a few mining sites in moun- tainous areas or in the Northwest receive 45 to 125 cm, plant growth at most western mine sites commonly is limited by water stress related to low precipitation. Also, precipitation often occurs as short - duration, high - intensity rainstorms or rapid snowmelt. Moderate to high infiltration and percolation rates in the upper part of the soil profile, which are influenced by organic matter levels and additions of mulch, are important for minimiz- ing erosion and maximizing water storage and intake. Again, higher organic matter levels increase infiltration rates and the water- holding capacities of soils with various textures. Also, vesicular ar- buscular mycorrhiza populations tend to increase the effective root surface area for absorption of water and nutrients. Both of these mitigative charac- teristics of organic matter tend to maximize the use of precipitation in semiarid areas. Effects of topsoil stockpiling on organic matter. Based on studies in North Dakota and Wyoming, long -term stockpiling is detrimental to topsoil in arid and semiarid mining environments (21). Four years after direct re- placement, native vegetation production on topsoil that had not been stock- piled was five times greater than that on a similar area covered with topsoil that had been stockpiled for 2 years. The researchers attributed the differ- ence to adverse changes in organic matter. Several factors affect humus formation in soil, and stockpiling affects many of these factors. Assuming the stripped area originally supported a dynamic plant community, the following factors of organic matter forma- tion are likely to be affected: soil organisms, moisture, temperature, 0 sup- ply, and plant material supply. The first and most obvious change occurring to buried topsoil is the loss of a large seasonal addition and smaller daily additions of dead plant tissue (future humus). After the initial decay of easily decomposable carbo- hydrates, amino acids, and proteins, more slowly decomposable lignins, tannins, fats, oils, waxes, and other substances continue to decay. Mi- crobial communities in the soil directly or indirectly compete with one an- other for the slowly declining supply of organic residues when moisture, temperature regime, and 0 supply are decreasing. The composition of mi- SOIL ORGANIC MATTER crobial communities changes as a (21, 40). Changes in organic matter leve cation within the stockpiled tops( out establishing vegetation on a t found the organic matter levels d the stockpile compared to the inte that the natural wetting and dry greater availability of organic r than on the interior of the stocl breaks down, water - soluble orga With respect to topsoil stockp that vesicular - arbuscular mycorr terior of the stockpile and that potential of the soil (65). Simila relatively few vesicular - arbuscula years old. In Wyoming one scien arbuscular mycorrhiza infection I age (52). Thus, vesicular - arbusc plant roots in the interior of the s certain interval of stockpile stor; In summary, the microbial po arbuscular mycorrhiza growth in time with reduced 0 levels, reduc supply, and loss of plants and rc sition of the readily decomposa followed by CO organic residuf responsible for this process in t and not deteriorate further (4). Soil sampling for organic mate tions, scientists use soil color a: content in soils with less than 12 tion factors that influence orga' soil map unit to the next, the th accordingly. As a result, under matter field characteristics (col that determine those characteri conditions. A taxonomically based soil st for field characterization of bas( the soil taxonomic system outli survey should be conducted by characteristics and soil - forming