The results of experiments involving direct comparisons of root and penetrometer resistance indicate that penetrometers experience two to eight times greater resistance than plant roots penetrating soil (Table 1). Dexter (1987) suggests that this ratio of penetrometer resistance to root resistance is positively correlated with soil strength, being greater in ‘stronger’ soils. At present there is neither theoretical basis for this suggestion nor sufficient published data to justify such a conclusion, although the need for accurate prediction of this ratio is clear. Indirect evidence.
