Pedogenetic and induced compaction in agricultural soils

For centuries, farmers have been observing the relationship between plants and their environment to develop the best means of cultivation and to ensure good production to meet human needs. In the past, most people were more concerned with the surface layer of the soil and they attached little importance to the role of subsoil or subsurface layers in crop or forest production. In recent years, however, with increasing pressure on land resources, we have started to pay more attention to what lies beneath the surface layer and to its effect on plant growth. Subsoil layers are extremely important to crop production, pasture management, forest growth, soil conservation, and the construction of buildings, highways, and airport runways. For agriculture, excessive compaction of subsoil is believed to cause or be related to some reduction in the productivity of many soils because deeper layers have important effects on soil moisture regime and aeration capacity. These subsoil layers may also supply certain plant nutrients. Furthermore, fertility and permeability of the subsoil have a direct influence on erosion hazards when soils are used for crop production (Nowland 1976). Undesirable compaction levels may be due to naturally occurring or genetically derived edaphic conditions (Winters and Simonson 1951) or due to "induced pans" caused by the manipulation of primary soil particles and aggregates by traction and tillage implements, such as the compression of soil by vehicular traffic (Raney et al. 1955). The mechanics of induced pans and their effect on plant response have been well documented, mainly in USA (Gill and Vanden Berg 1968, Rosenberg 1964, Barnes et al. 1971). A recent series of articles (Voorhees 1977, Robertson and Erickson 1978) describes the problem in more popular language. This bulletin deals primarily with soil compaction problems, especially in Eastern Canada. However, where necessary and appropriate, more recent and relevant work from elsewhere is included.