Effect of Soil Texture on Critical Bulk Densities for Root Growth1

Published and unpublished data from 10 studies were analyzed to determine the effects of soil texture on critical bulk densities for rooting at near-optimum soil water contents. Highly significant neg- ative relationships were found between percentage clay or silt + clay and the bulk density at which rooting was at a maximum or the bulk density at which rooting was 0.2 of that maximum. Similar relationships were also found between percentage clay or silt + clay and (i) the bulk densities of soil layers classified as fragipans and (ii) the maximum bulk densities at which "many" roots are reported in U.S. Soil Conservation Service pedon descriptions. Thus, soil texture can be used to estimate bulk densities of fragipans and crit- ical bulk densities at which root growth is severely affected at near- optimal soil water contents.