Root Extension in a Longleaf Pine Plantation

Root extension in a 24—year—old longleaf pine plantation in the North Carolina sandhills was studied by the application of 10 mc of I 1 3 1 directly to the soil, on the surface, or at depths of 1 or 3 ft, and surrounding trees monitored with a portable scintillation counter. Within 10 ft of the point of application, all trees above 3.0 inches absorbed I 1 3 1 in sufficient quantities to be detected. Beyond 22 ft for surface applications, and 33 ft for 1— and 3—ft depths, no I 1 3 1 was detected in any trees. Regressions were computed to determine whether root extension could be predicted. When distance from the point of application was used as the dependent variable, an index of competition and the angle from the tree row proved to be the most useful, to the exclusion of the various measures of tree size.