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U.S. DEPARTMENT OF AGRICULTURE PAGE 3 OF 4 <br /> �URAL RESOURCES CONSERVATION SERVICE 01/28/97 <br /> ' PHYSICAL PROPERTIES OF SOILS <br /> note -- PHYSICAL PROPERTIES OF SOILS--Continued <br /> ORGANIC MATTER is the plant and animal residue in the soil at various stages of decomposition. In report J. <br /> estimated content of organic matter is expressed as a percentage, by weight, of the soil material that is <br /> s than 2 millimeters in diameter. The content of organic matter in a soil can be maintained or increased by <br /> returning crop residue to the soil. Organic matter affects the available water capacity, infiltration rate, and <br /> Ith. It is a source of nitrogen and other nutrients for crops. <br /> EROSION FACTOR K indicates the susceptibility of the whole soil (including rocks and rock fragments) to <br /> eet and rill erosion by water. Factor K is one of six factors used in the Universal Soil Loss Equation (USLE) <br /> predict the average annual rate of soil loss by sheet and rill erosion in tons per acre per year. The <br /> imates are based primarily on percentage of silt, sand, and organic matter (up to 4 percent) and on soil <br /> structure and permeability. Values of K range from 0.05 to 0.69. The higher the value, the more susceptible <br /> Isoil is to sheet and rill erosion by water. <br /> EROSION FACTOR Kf is like EROSION FACTOR K but it is for the fine-earth fraction of the soil. Rocks and <br /> k fragments are not considered. <br /> SION FACTOR T is an estimate of the maximum average annual rate of soil erosion by wind or water that can <br /> occur without affecting crop productivity over a sustained period. The rate is in tons per acre per year. <br /> I ERODIBILITY GROUPS are made up of soils that have similar properties affecting their resistance to wind <br /> erosion in cultivated areas. The groups indicate the susceptibility of soil to wind erosion. Soils are grouped <br /> �ording to the following distinctions: <br /> 1. Coarse sands, sands, fine sands, and very fine sands. <br /> ' These soils are generally not suitable for crops. They are <br /> extremely erodible, and vegetation is difficult to <br /> establish. <br /> ' 2. Loamy coarse sands, loamy sands, loamy fine sands, loamy <br /> very fine sands, and sapric soil material. These soils are <br /> very highly erodible. Crops can be grown if intensive <br /> ' measures to control wind erosion are used. <br /> 3. Coarse sandy looms, sandy looms, fine sandy looms, and <br /> very fine sandy looms. These soils are highly erodible. <br /> Crops can be grown if intensive measures to control wind <br /> erosion are used. <br /> ' 4L. Calcareous looms, silt looms, clay looms, and silty clay <br /> Looms. These soils are erodible. Crops can be grown if <br /> intensive measures to control wind erosion are used. <br /> ' 4. Clays, silty clays, noncalcareous clay loams, and silty <br /> clay foams that are more than 35 percent clay. These soils <br /> ' are moderately erodible. Crops can be grown if measures to <br /> control wind erosion are used. <br />