Modeling the Influence of Water Content and Bulk Density on Soil Penetration Resistance.

A cone penetrometer is a simple and inexpensive device for rapid assessment of soil strength based on penetration resistance or cone index. The soil penetration resistance (PR) is an important soil property. It correlates with crop growth and yield potential and is a useful tool to evaluate the impact of tillage operations. The soil PR is directly correlated to bulk density (BD) and exhibits an inverse relationship to soil water content (WC) or matric potential. In addition, soil parameters such as texture, organic matter content and mineralogy affect soil PR readings. The objective of the presented study is to provide a better understanding of the effects of WC and BD of differently textured soils on PR readings in the field. To capture a wide range of conditions, PR, WC and BD were measured for 5 field soils during dry and wet seasons. Obtained data were evaluated with standard empirical models and a new general relationship was proposed with PR expressed as a power function of the degree of saturation and normalized bulk density.