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limitations . The limitations may result from the effects of <br /> one or more of the following : (1) Moderately steep slopes ; <br /> (2) high .susceptibility to water or wind erosion or severe <br /> adverse effects of past erosion; (3) frequent overflow <br /> accompanied by some crop damage; (4) very slow permeability <br /> of the subsoil; (5) wetness or some continuing waterlogging <br /> after drainage; (6) shallow depths to bedrock, hardpan, <br /> fragipan, or claypan that limit the rooting zone and the <br /> water storage; (7) low moisture-holding capacity; (8) low <br /> fertility not easily corrected ; (9) moderate salinity or <br /> sodium; or (10) moderate climatic limitations . <br /> When cultivated , many of the wet, slowly permeable but <br /> nearly level soils in Class III require drainage and a <br /> cropping system that maintains or improves the structure and <br /> tilth of the soil . To prevent puddling and to improve <br /> permeability it is commonly necessary to supply organic <br /> material to such soils and to avoid working them when they <br /> are wet . In some irrigated areas , part of the soils in <br /> Class III have limited use because of high water table, slow <br /> permeability, and the hazard of salt or sodic accumulation . <br /> Each distinctive kind of soil in Class III has one or more <br /> alternative combinations or use and practices required for <br /> safe use, but the number of practical alternatives for <br /> average farmers is less than that for soils in Class II . <br /> Class IV - Soils in Class IV have very severe limitations <br /> . that restrict the choice of plants , require very <br /> careful management , or both . <br /> The restrictions in use for soils in Class IV are <br /> greater than those in Class III and the choice of plants is <br /> 39 - 4- <br />