The compactness of agricultural soil may vary greatly during a crop season due to tillage and other machine operations that apply forces to the soil. Thus, an adequate model for agricultural soil compaction must be capable of predicting soil density over a wide range of compactness, from a very loose state to a very compacted state. The traditional logarithmic model does not adequately predict soil density at low levels of compactness and low stress levels. A three-parameter multiplicative model of soil compaction is proposed. This model satisfies certain boundary conditions for natural volumetric strain at low and high stress levels which are not satisfied by the traditional model. The model was fitted to hydrostatic compression test data for two agricultural soils, a sandy loam and a clay. The model was capable of predicting soil density at low stress levels with less error than the traditional model. Data from three levels of moisture content of the clay showed that all three coefficients of the proposed model were influenced by moisture content.

Custom Prescribed Tillage (CPT), is a concept which focuses on the requirements of the crop, and is based on the premise that, to meet future needs of productivity, conservation, and efficiency, tillage systems will be described for specific crops or varieties, soil types, soil conditions and environmental conditions. CPT is a dynamic control system with feedback. Examples are given of the use of the CPT concept in research to enhance crop production.

Prescribed tillage to meet agronomic needs will be important to future goals of productivity, energy efficiency, and resource conservation. Control systems will be an important feature of the tillage systems that are developed to implement prescribed tillage. A control concept for tillage systems is described.