Abstract Growth of horizontal roots, height, and dbh of five selected lines and three bulk-seed lots of planted slash pine ( Pinus elliottii var. elliottii ) were followed through the third, fourth, and fifth years in the field. Treatments were irrigation, cultivation, and fertilization, singly or in combination. Root growth responded to soil temperature and rainfall but was not significantly affected by treatment except for rapid regrowth of roots cut by cultivation. Significant differences in root length among lines disappeared by the end of the fourth year. Mean annual growth of the 256 roots was 56, 38, and 31 inches for the 3 years, respectively, with variations from 0 to more than 140 inches during the third year and lesser maxima in the following years. Trees were 15 to 18 feet tall at 5 years, corresponding to site index 70 at 25 years. Responses of height and diameter to treatment were limited except for diameter increases due to fertilization during the final year. Responses to cultivation and fertilization for height and for dbh among lines were highly significant.
C. M. Kaufman (Sun,) studied this question.