Soil macrostructure as affected by cultural treatments

Abstract

Abstract does not appear. First page follows. Introduction This investigation was undertaken to find a quantitative method of expressing the structural condition of the soil, and by means of this method to study the effects of various mechanical treatments with respect to changes in structure. The effects of irrigation and of tillage operations were of particular concern. Seasonal changes were also observed. Shaw (17)3 has defined soil structure as: A term expressing the arrangement of individual grains and aggregates that make up the soil mass. The structure may refer to the natural arrangement of the soil when in place and undisturbed or to the soil at any degree of disturbance. The terms used indicate the character of the arrangement, the size and shape of the aggregates, and in some cases may indicate the consistence of those aggregates. As thus defined, the term “soil structure” is obviously descriptive, and as such is not capable of being expressed by any specific measurement or number. Many measurements of the physical properties of soils, which are dependent on the structure, have been made; and any of these measurements may be considered as an index of soil structure. These measurements are made either of the macro- or microstructure. A greater amount of work has been done on the microanalysis, which has been mainly measurements of the size distribution of particles after the soil has been slaked in water. The macroanalyses have been mainly measurements of the size distribution of coarse aggregates of soils obtained under field conditions in an undisturbed state. This present investigation is of the latter type; the method will be described in detail later. Other methods, such as the pull on the drawbar of a tillage implement, the amount of pressure required to force a sharpened instrument into the soil, and porosity measurements such as water penetration, air movement, so-called “capillary and noncapillary” pore space, and measurements of volume weight, have been used as indexes of soil-structure.