The dynamics of organic matter in grassland soils

MAINTENANCE of soil organic matter in semiarid agroecosystems is important. Organic matter is a source of, and temporary sink for, several plant nutrients. It also is important in maintaining soil tilth, abetting infiltration, promoting water retention, and reducing wind and water erosion. Reductions in organic matter following cultivation of grassland soils are reasonably well documented ( 32, 34, 51 ). That is important because the organic matter portion of the global carbon pool, estimated at four times that present in biota or the atmosphere, makes carbon from organic matter significant to global carbon flows ( 16, 62, 81 ). We reviewed the research pertaining to organic matter in semiarid grassland soils with emphasis on studies relating organic matter characteristics to soil environment. These studies are descriptive in nature and help us understand the behavior of organic matter in soil (39). Transformations of the organic fraction are considerably influenced by inorganic components (30), and soil is a three-dimensional body in equilibrium with its environment; therefore, studies of the whole soil system are emphasized. Less emphasis is given ...