Spodosol Morphology As a Governor of Loblolly Pine Needle and Shoot Dieback and Its Response to Cultural and Genetics.

Needle and shoot dieback (NSD) is a disease of unknown origin that kills needles, and in the most severe cases terminal buds, of young intensively managed loblolly pine (Pinus taeda) trees thereby lowering primary production in young plantations and potentially wood quality with time.  We censused NSD symptoms after the second growing season in two plantations (part of the FBRC-SSIGNS installations) established on Spodosols.  In Alachua Co, Fl we found that the spatial distribution of NSD was highly structured, and that micro- and macro-nutrient addition significantly decreased NSD occurrence (p<0.05).  In contrast, in Wayne Co, Ga we found the spatial distribution of NSD to be poorly structured and that NSD occurrence was not affected by fertilization.  At both installations loblolly pine genetics was significantly related to NSD (p<0.05) but the best and worst performing families did not overlap across the sites. 

Inter-site variability suggests that another, yet unaccounted for, factor varies between the sites to influence NSD and its relationship to fertilization and genetics.  We’ve hypothesized that the depth to the Bh horizon is this factor, and expect that as the depth to the Bh increases so too do nutrient limitations (or imbalances) associated with NSD.  To test this hypothesis we are chemically analyzing foliage and soils to understand the nutritional aspects of NSD and to quantify how nutrient availability varies vertically through these Spodosols depending on the depth of the Bh.  Chemical analyses are being coupled with geostatistical analysis to examine if and why NSD and the depth to the Bh are spatially correlated across these landscapes.  Our findings will elucidate the underlying mechanisms of a disease that plagues young southern pine plantations and also provide a rare glimpse into the vertical and horizontal variability of soil and subsoil nutrient supply in Spodosols.