QUANTIFYING THE INFLUENCE OF CROPPING HISTORY ON SOIL STRUCTURE

Abstract

Information on rates of change of the structure of different soils under different cropping systems is vital to research in soil conservation. Much data on soil structure cannot be used to provide information on rates of change because of an inability to relate measurements at a given time to cropping history. A conceptual model is presented which facilitates quantification of cropping history in relation to soil structure. The model relates structural form, structural stability, stabilizing materials, biological factors and forces which may be exerted on the soil. Soil and crop management practices influence the nature and magnitude of forces involved, biological factors, and the level of stabilizing materials. The model is applied, for illustrative purposes, to five different cropping treatments involving the production of corn and bromegrass grown for different lengths of time over a 15–yr period. Functions to describe the accumulation or loss of stabilizing material under the two different cropping systems are assumed and functions describing the relations between calculated levels of stabilizing materials and structural stability, and between structural stability and structural form are then presented. The model provides a framework for expressing the impact of soil and crop management practices on soil structure and includes variables which could be used for assessing the "quality" of soil under current conditions. It also provides a method for characterizing the susceptibility of soils to structural change arising from soil and crop management practices. Extensive research is required to evaluate the model, however potential applications justify the effort which will be required. Key words: Tensile strength, wet aggregate stability, compaction index, corn, bromegrass, soil conservation