Impact of Nitrogen on Vegetative Growth of Mature Peach Trees in a Subtropical Climate

The Florida peach industry has rebounded from devastating freezes in the 1980s with increasing production and acreage.  As the main production area shifts into southern areas with a subtropical climate, fertilization regimes developed in temperate climates may not fulfill the nutritional demand of trees planted in these new production areas with extended vegetative growth periods after harvest.  The objective of this research was to examine the effect of different nitrogen rates on peach tree growth in a subtropical climate to determine the optimal rate of nitrogen. Four rates of nitrogen (N) plus a control (0 kg. N/ha) were applied to six-year-old ‘TropicBeauty’ peaches budded onto ‘Flordaguard’ rootstock in Citra, FL and included:  45 kg·ha^-1, 90 kg·ha^-1, 179 kg·ha^-1, and 269 kg·ha^-1annually during the 2011 and 2012 growing season.  Vegetative growth measurements included trunk cross-sectional area (TCSA), vegetative and floral bud distribution on 1-year-old growth, pruning weights, total leaf nitrogen content (%), and chlorophyll content. The TCSA measurements revealed no differences, however; trees in treatments with 0, 45, and 90   kg·ha^-1 tended to be smaller than those receiving 179 and 269 kg·ha^-1 annually.  Trees with 0 and 45 kg·ha^-1 produced lower tended to have lower pruning weights; however, there were no statistical differences after two years.  Vegetative and floral buds were fewer in the low nitrogen rates (0 and 45 kg·ha^-1) with high numbers of blind nodes present in all treatments. Total leaf nitrogen (%) was lower in the 0 and 45 kg·ha^-1 treatments (3.7%) than the highest two N treatments (4.1%).  These results indicate that although trees in the lowest N treatments contained seemingly adequate amounts of nitrogen, decreasing vegetative and floral buds over subsequent years may lead to smaller trees with reduced yield, while trees with higher rates of N produced more blind notes, requiring more severe pruning to maintain productivity.