Shoot and foliage growth phenology of loblolly pine trees as affected by nitrogen fertilization

Abstract

Effects of N fertilization on shoot phenology and foliage production were determined in loblolly pine ( Pinus taeda L.) trees growing in the Georgia Piedmont. Two rates of N fertilizer were applied in February 1991. Shoot and foliage growth were determined at upper, middle, and lower crown positions at 1-month intervals throughout 1991. Shoot elongation of individual flushes overlapped, although there was about a 1-month delay between the initiation of each successive flush. Needle elongation was closely associated with shoot elongation but lasted 2 months longer. On average, the first flush contributed about 69% to total leaf area. Shoot and foliage growth increased with crown height. Shoot elongation, needle length, number of fascicles per flush, and leaf area per flush were 9.7, 1.4, 4.7, and 6.9 times higher, respectively, in the upper crown than in the lower crown. The effects of N fertilization on shoot and foliage growth were most pronounced in the middle crown position. Leaf area production per shoot was increased by 12.4, 66.4, and 41.1% by fertilization for shoots in the upper, middle, and lower crowns, respectively. N fertilization did not alter the seasonal patterns of shoot and foliage development. Both fertilized and control trees began, peaked, and ended flush and fascicle elongation concurrently.