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

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DOPER ido no Dercent slopes (loamy texture) ncorporated or in -situ reduces gh organic matter levels are 25 ow organic matter levels. Ap- 3.0 t /ha probably will reduce id and semiarid West annual e a few mining sites in moun- 125 cm, plant growth at most y water stress related to low curs as short - duration, high - derate to high infiltration and 1 profile, which are influenced ch, are important for minimiz- ed intake. ;ase infiltration rates and the is textures. Also, vesicular ar- rease the effective root surface oth of these mitigative charac- ze the use of precipitation in matter. Based on studies in kpiling is detrimental to topsoil 21). Four years after direct re- opsoil that had not been stock - -nilar area covered with topsoil searchers attributed the differ- n soil, and stockpiling affects ed area originally supported a :tors of organic matter forma - moisture, temperature, 0 sup- ing to buried topsoil is the loss additions of dead plant tissue f easily decomposable carbo- slowly decomposable lignins, ances continue to decay. Mi- idirectly compete with one an- ganic residues when moisture, asing. The composition of mi- SOIL ORGANIC MATTER 205 crobial communities changes as a result, and populations generally decline (21, 40). Changes in organic matter levels relate to the duration of storage and lo- cation within the stockpiled topsoil. After 31/2 months of storage and with- out establishing vegetation on a topsoil stockpile, Klein and associates (40) found the organic matter levels declined (1.0% to 0.2 %) on the margins of the stockpile compared to the interior of the pile. The researchers concluded that the natural wetting and drying on the margins of the pile facilitated greater availability of organic matter to microbiological decomposition than on the interior of the stockpile. As cellulose within the plant tissue breaks down, water - soluble organic C presumably increases (21). With respect to topsoil stockpiling, one group of researchers concluded that vesicular - arbuscular mycorrhiza losses occur from topsoil in the in- terior of the stockpile and that 3 years of storage reduced the infection potential of the soil (65). Similarly, Christensen and Allen (22) recovered relatively few vesicular - arbuscular mycorrhiza spores from stockpiles over 5 years old. In Wyoming one scientist found that the potential for vesicular - arbuscular mycorrhiza infection (growth) declined with increasing stockpile age (52). Thus, vesicular- arbuscular mycorrhiza are limited by a lack of plant roots in the interior of the stockpiles and apparently can endure only a certain interval of stockpile storage (44). In summary, the microbial populations, organic C levels, and vesicular - arbuscular mycorrhiza growth in the margins of topsoil stockpiles decline in time with reduced 0 levels, reduced soil moisture, changes in organic matter supply, and loss of plants and roots. Upon relatively immediate decompo- sition of the readily decomposable organic substances, NH3 is produced, followed by CO,, organic residues, and humus. At this point, the organisms responsible for this process in the stockpiled topsoil should be less active and not deteriorate further (4). Soil sampling for organic matter characterization. During field investiga- tions, scientists use soil color as the principal indicator of organic matter content in soils with less than 12 percent organic matter. As the soil forma- tion factors that influence organic matter characteristics change from one soil map unit to the next, the thickness and color of the A horizon changes accordingly. As a result, understanding the relationship between organic matter field characteristics (color and horizon thickness) and the factors that determine those characteristics is essential for characterizing baseline conditions. A taxonomically based soil survey and sampling program should be used for field characterization of baseline organic matter conditions, specifically, the soil taxonomic system outlined by the Soil Survey Staff (77). The soil survey should be conducted by a soil classifier familiar with organic matter characteristics and soil - forming factors of the mine permit area. The sam-