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

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202' SMITH, REDENTE, and HOOPER aid revegetation efforts. Organic matter can be separated into two general fractions: stable and dynamic (26). The stable fraction has an equilibrium level that varies with geographic location. Little can be done to increase this stable fraction. Thus, temporary increases must be directed at changing the dynamic fraction, such as bringing organic matter to the site (exogenous) or growing cover crops. The applied organic matter should have a C/N ratio as close to the target level of the soil as possible. Otherwise, N applications may be necessary to compensate for immobilized N. Even leguminous mulches have C/N ratios of about 18:1 or greater, much higher than average soil ratios of 10:1 (4). Some straw mulches and wood residues in the western United States have C/N ratios as high as 2,000:1 (4). Alternatively, areas amended with mulches or residues that have high C/N ratios can be left fallow, allowing the area to return to an "available N" condition. But such an alternative may not be feasible because controlling weeds that may invade the area may be more costly than N fertilization. The amount of organic matter applied should be consistent with the in- tended effects on topsoil, seedling establishment, and continued plant growth. If the purpose is to provide nutrients for plant growth, rather size- able amounts may be required, depending upon the type of organic matter applied. If the purpose is to improve physical condition of the topsoil, smaller amounts may suffice. Recommended amounts that provide some plant nutrients and improve physical conditions vary considerably, but generally start at 0.5 t /ha. Timing and frequency of application should be consistent with the in- tended effect on plant growth medium. Generally, a one -time application improves physical condition and provides some nutrients. Even if organic matter levels in the topsoil are relatively high, a one -time application pro- vides some benefits, particularly on soils that are low or high in clay con- tent. Adverse effects of applying organic matter in the form of straw mulch in- clude the possible immobilization of N during decomposition (7), intercep- tion of light, and possibly a physical barrier to seedling development (39). Also, litter accumulation on minesoil may result in a formation of high C/N ratio and /or stagnation of plant succession at an early seral stage (68). But one study indicated that these potential problems can be minimized (30). Mechanical means are the best methods to apply mulches, wood wastes, composts, sludge, and other organic matter. Material should be incorporat- ed into the upper 15 cm of soil. Except in low precipitation (< 25 cm /yr) areas, an effective method of mulch incorporation is planting an annual nurse crop the year prior to seeding. Mowing or disking the crop in the fall adds residues to the soil and creates a physical barrier to trap snow and re- duce runoff in the spring. There has been little research in the West regarding permanent increases SOIL ORGANIC MATTER in organic matter levels. Eastern tions, but sound recommendatior the West are only speculative. In recent years a new technique mines in northwestern Colorado. matter content of the dynamic fra ment activities. It involves "rotoc including trees (aspen up to 50 cn into the top 40 cm of the soil prof communication, T. Johnson, Col Springs, Colorado, and J. Mona pany, Denver, Colorado). Rotocl 3 -m wide, 9,525 -kg rototiller -like dozer. This action incorporates si ganic material into the topsoil. 1 small tree stems with high C/N ra able leguminous plants with low ( of soil follows soon thereafter (1. and second -year revegetation has and replacing this material is unk used long enough to observe rev( Erosion. A primary goal of rel Reducing erosion is very impor matter in the surface horizon. Er matter. Usually, eroded material matter and N as undisturbed soil therefore, is more susceptible is splash than to clay or quartz min( tion of organic matter in eroded Organic matter in the form of r the soil erodibility and crop mar equation. Therefore, the higher t plant growth medium, the lower rates for two similar- soils having same management and vegetatioi tion will differ by 50 percent; tl higher erosion rate (1, 88). Thi! organic matter increasing the ini Research regarding effects of water erosion have shown that r cantly reduce water erosion. Ne straw reduced erosion 93 percen (32). In western North Dakota er 9 percent slope on which 4 t /ha