Design and Use of Machinery to Loosen Compact Soil

Abstract Extensive demand for information on methods and equipment for subsoiling and loosening compacted layers of soil has been a major factor in the development of a cooperative program of research between soil scientists and agricultural engineers in the United States Department of Agriculture and the state experiment stations. The engineering part of the program is directed towards mechanically producing soil conditions found desirable by the soil and plant scientists. It is based upon soil and machine relationships and has the objectives of (1) preventing the formation of compact layers by machine traffic and (2) the development of equipment and methods of use for loosening compacted layers when formed. The engineering program consists of (a) field studies and experiments with various commercial subsoilers and sweeps, (b) laboratory studies of the relationships of elements of design to the reactions of a range of soils in various conditions whose physical properties are measured, and (c) the production and testing of experimental designs based upon information gained from the field and design studies. The soil physical properties found to relate most directly to design are resistance to compression, shear value, modulus of rupture, and arch action (defined as the vectoring out through a mass of soil of pressures applied to the surface). Design elements are evaluated first by determining the reaction of moist sand where light stresses result in visible strains permitting a “qualitative” appraisal of the pressures generated by the implement. Quantitative evaluation of the design elements is obtained by testing against heavier soils having known physical properties.