SOIL FRIABILITY - THEORY, MEASUREMENT AND THE EFFECTS OF MANAGEMENT AND ORGANIC-CARBON CONTENT

The weakest link between particles or aggregates determines the streng th of soil. We have re-examined the theory and, as a result, have re-d efined friability, F, as the coefficient of variation of soil tensile strength. The formal relationship between the parameter i/alpha of the weakest link theory of strength, which has previously been used as a measure of friability, and the newly defined measure, F, is described by a simple equation which has an accuracy of within 2% over the range of interest. The quantity F is used to show that friability reaches m aximum at water contents around the lower plastic Limit, that mechanic al disturbance of wet soil by tillage reduces the friability, and that friability is strongly positively correlated with the organic carbon content of the soil. These results show the merit of measuring friabil ity for determining the optimum water content for tillage, for quantif ying the damage done by different tillage practices, and as a theoreti cally based index of soil physical quality.