Seasonal development of loblolly pine lateral roots in response to stand density and fertilization

In 1989, two levels each of stand density and fertilization treatments were factorially established in a 9-year-old loblolly pine plantation on a P-deficient Gulf Coastal Plain site in Rapides Parish, Louisiana, USA. In 1995, a second thinning was conducted on the previously thinned plots and fertilizer was re-applied to the previously fertilized plots. The morphology of new long lateral roots was evaluated at 2-week intervals in five Plexiglas rhizotrons per plot of two replications. The overall objective of this study was to evaluate the seasonal initiation of six morphological categories of long lateral roots (≥ 2.5 cm in length) in response to stand density and fertilization. Lateral root development exhibited a seasonal pattern with the initiation of branched lateral roots predominantly occurring in spring and summer. The initiation of non-branched lateral roots occurred throughout the year regardless of season. Stand density did not affect lateral root morphological development. However, fertilization stimulated the initiation of branched lateral roots that were greater than 1 mm in diameter.