What Can Models of Penetrometer Resistance Tell Us about Soil Conditions for Root Growth?.

Recently there has been considerable interest in the development of empirical model to predict the penetrometer resistance of soil. Penetrometer resistance is widely used as a measure of the mechanical impedance that roots experience in either drying or compacted soil. However, there are relatively few simple models to predict penetrometer resistance that can be applied without detailed knowledge of soil texture, organic matter content, soil water status, density or other soil variables. It would be useful if it were possible to predict the effects of structure, compaction, depth and soil drying on penetrometer resistance with a parsimonious model. We describe the development of model for penetrometer resistance based on the premise that it is proportional to the small strain shear modulus, G.  The model was developed using laboratory data from a range of soils, but then tested with field data from the UK and NE China. Although the parameters of the model were relatively insensitive to soil type, the model did need to be fitted to data from different field sites to obtain the most accurate description of field data. The semi-empirical nature of our model allowed us to draw inferences about the effects of soil management on penetrometer resistance. We explore the scope for future developments and place our work in context with other recently published accounts.   Specifically, we consider what penetrometer resistance models tell us about soil conditions for root growth.