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

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196 the degree of organic matter decomposi fr - ` -, is- ing decomposition (14). As soil reaches oil organic matter level is relatively constant. Regardless of soil conditions, the direct effects of organic matter are the same: generally, plants respond favorably because nutrients, especially N, are provided through decomposition and mineralization (43). Campbell stated, "Crop yields are often directly proportional to the N released from organic matter, the other nutrients are also important but N is required in much larger amounts and is more likely to be deficient" (15). Effects on soil. Soil organic matter directly or indirectly influences the physical environment (4). As the percentage of organic matter decreases in a given soil, the bulk density increases, with an associated reduction in poros- ity. The combination of increased bulk density and reduced aeration restricts root growth, impairs normal root absorption, and inhibits micro- biological activity. Soil structure greatly influences fertility (42). Organic matter is one of the most important factors in soil structure development. Soils with good struc- ture provide the best conditions for supplying water and nutrients to plants (42). The best water and nutrient regimes occur in soils with granular struc- ture in which the aggregate size is 1 -2 mm. Such soil structure is formed most readily under a mixture of perennial grasses and legumes. The prerequisites for the formation of good soil structure include (1) consolida- tion of the soil particles under pressure from highly branched root systems of grasses, (2) the formation of humin and humic acid, (3) penetration into the soil crumbs of the highly dispersed solutions of humin and humic acids, and (4) conversion of these acids into a cohesive soil aggregate by means of Ca supplied by the legume roots (42). Also critical is the fact that conversion of humus substances into a soil aggregate is irreversible under natural processes (42). After plowing or disk- ing, formation of humus substances that bind soil crumbs is slow and re- quires a specific environmental condition (42). Similarly, increased stability of aggregates usually accompanies an increase in organic matter (15). Thus, to maintain good soil structure there must be an absence of continued plow- ing and a source for newly formed humus substances on a regular basis. Incorporation of manure into soil influences microorganism activity. Organic material itself, without biological transformation, has little effect on soil structure. Microorganisms, without organic materials as a source of energy, are ineffective in producing soil aggregation. Fungi and actinomy- cetes produce mycelia and have metabolic processes that synthesize complex organic molecules. Decomposition products remain in the soil. The sum of these effects is the production of stable soil aggregates. This stability, therefore, can result from the mechanical binding action of the cells and filaments of the organisms; cementation effects of the products of micro- SOIL ORGANIC MATTER bial synthesis; and the stabilizint Organic matter usually impro proves drainage in fine - textured deeper root systems. Collectively ability and the water use efficie plant species, soil type, and clim effects of organic matter may in matter in general increases plant Organic matter increases infilti surface long enough for it to en condition of the soil. Organic n increases the rate of infiltration. soil, eventually improving soil increases. Contrary to this gene; increasing infiltration, some fo because of the presence of hydro One of the most important ch tain and exchange positively primary controlling factors of c: clay and the quantity of organic in most mineral soils accounts fc exchange capacity (15). In sandy the cation exchange capacity is A buffer solution is one that acid or base. Soils behave like be colloidal properties associated • hold H, Al, and other cations (, soils with lower organic matter 1 matter levels. There is a wide range of chemi ing metal cations into weakly ioi ing agents —occur naturally in organic fraction as well as soli, Organic matter can hold meta chelation (15). In soils having n plants, chelation may hinder ad the metallic ion. Soil organic matter and re Because virgin organic matt within a particular mine site, t levels for organic matter to rat( The same is true of surface soil 1