Two studies investigated the effects of fall nitrogen fertilizer applications on the root growth potential (RGP) and field performance of container loblolly pine seedlings (Pinus taeda L.). The seedlings were sampled at 4 chilling levels ranging from 100 to 550 hours (0 to 8' C). Seedlings propagated for the first study may have had a hidden nutrient deficiency and therefore the fall diammonium phosphate (DAP) application at rates of 202 kg N/ha and 67 kg N/ha increased RGP 43% and 32%, respectively. The growing season mineral fertilizer application rate was increased in the second study which may explain why nitrogen applications at 202 kg N fall/ha did not increase RGP. In general, RGP increased as exposure to chilling hours increased. Fall fertilization increased total seedling weight. Analysis of covariance indicated that RGP may be a function of total seedling weight and not a direct response to fertilizer treatment or chilling level. For the first study, survival was not significantly affected by the fall DAP treatments.
Williams, Hans Michael and South, David B., "Root Growth Potential and Field Survival of Container Loblolly Pine Seedlings Fall Fertilized with Nitrogen" (1995). Faculty Publications. 242.