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

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SMITH, REDENTE, and HOOPER lant material (4), and releasing rthworms in arid and semiarid =prise half a soil's biomass. ar. Beetle grubs and other soil narid soils in the West do not ms (24). warm, and slightly alkaline to ) etter in drier soils with a neu- num soil conditions for fungi noist and warm soils. Yeasts, f stockpiled topsoil (E. Allen, mmunication). -borne fungi that invade the iotic relationship. The mycorr- crease the surface area for ab- nbiosis the mycorrhiza fungus ant provides favorable growth • the fungi (21). )pulations in soil because plant soils are either stored for long poil and subsoil material (44). Ipagule numbers and infection undisturbed areas (3, 23, 78). can be very slow because the )hysical changes in soils caused iluted with chemically undesir- ;anic matter derives from plant , plants supply large amounts of decomposed by soil organisms ;, either by leaching or physical mains with the soil. If incorpo- eater water infiltration and ero- greater when crop remains are ;oil surface. Root remains are ots are better sources of C, with as roots decompose they build nutrients, is an excellent source oil tilth, improve water infiltra- tnic matter content in some soils er and 20 to 50 percent volatile 191 SOIL ORGANIC MATTER solids. Thus, an application of 10 kg /ha would supply 1 to 4 kg of organic matter. Aged manure and compost decompose slowly because they are us- ually well rotted already. Aged manure can also serve as a growth stimulant, influencing the growth and development of plants and, in turn, yield (8). But applications of green manure extraction have retarded seedling ger- mination and development (73). Peat and mineral fertilizers can be combined effectively to improve soil conditions and plant growth. (Peat is undecomposed or slightly decom- posed organic matter accumulated under conditions of excessive moisture.) Adding peat to a soil can improve water - holding capacity, increase aeration and water infiltration in fine - textured soils, provide a material capable of absorbing and retaining plant nutrients in an available form, improve root penetration, and increase a soil's buffering capacity (46). Sewage sludge contains about 50 percent organic matter and can, there- fore, be used to build and maintain fertile soil from spoil or soil (83, 84). Municipal sewage sludge can be applied in liquid or solid form in sufficient quantity to rebuild disturbed soil with one application (33). There are con- cerns about using sewage sludge as a soil amendment. Metallic elements in the sludge can be toxic to plants and eventually enter the food chain. Also, the applied sludge can increase the soluble salt concentration sufficiently to retard plant growth (83). Many sewage sludge amendment studies and ap- plication guidelines exist (33). Wood wastes can be effective sources of organic matter. In theory, add- ing wood wastes to soil may have a depressing effect on plant growth because N may be immobilized. But data indicating immobilization are scarce. It may be necessary to add N with wood wastes to provide additional N for plant growth. Addition of wood wastes to soil has many positive ef- fects on the physical properties of soil, such as improved friability with de- composition, which improves infiltration and subsequent water storage (72). Methods of analyzing organic matter. Because the total weight of C with- in soil organic matter (passing a 2 -mm mesh sieve) is 48 to 58 percent, or- ganic C often is used to estimate organic matter. Organic matter is estimat- ed by multiplying organic C times 1.724 (58). Broadbent suggested this fac- tor should be 1.9 and 2.5 for surface horizons and subsoils, respectively (11). Other researchers recommended that the appropriate factor be deter- mined experimentally for each soil (58). These same researchers also sug- gested that reporting only laboratory data on organic C is more appropriate than estimating organic matter unless the correction factor is presented with organic matter values. But Allison (4) concluded that using a correction fac- tor to estimate organic matter is not objectionable "if extreme accuracy is not required." There are three methods for determining organic C (58): (1) analysis of