Nitrogen Rate and Form Effects Growth and Yield of Southern Highbush Blueberry in Pine Bark Beds

Two southern highbush blueberry (SHB) cultivars, ‘Emerald’ and ‘Jewel’, were used to study the effects of three nitrogen fertilization rates and two nitrogen forms on growth and berry yield. The SHB cultivars were grown in 0.9 m wide by 15cm deep pine bark beds at the University of Florida Plant Science Research and Education Unit in Citra, FL.  The planting was established in 2006 and the experiment was initiated in March, 2008. Plant Spacing was 0.91 m in rows and 3.05 m between rows. Randomized complete block designs were used with a fertilizer rate by fertilizer type factorial arrangement of treatments. The two cultivars were not inter-planted and thus represent separate experiments. Treatments were applied to 4-plant plots using one of the center plants as the data plant. Annual nitrogen rates were 54.7 g N/plant, 78.1 g N/plant, and 101.5 g N/plant. For fertilizer type, the N was applied either as ammonium sulfate (AS), or as 50 % AS and 50% sulfur coated urea (SCU). AS is a highly soluble fertilizer whereas, SCU is a slow-release fertilizer. Fertilizer applications were divided evenly into 8 monthly applications beginning in mid-February and continuing through September. All applications were applied by hand. Phosphorus, potassium and micronutrients were applied at equal rates to all plants per current recommendations. Irrigation was applied daily using micro sprinklers and was based on a function of evapotranspiration. Fruit was harvested every 3-4 days beginning in early April and continuing through May. Canopy volumes were measured at the end of each growing season when plants were dormant. There were no effects of fertilizer rate or type on fruit yield during 2008 or 2009. In winter of 2008-2009 moderate freeze damage to flowers and broken canes from excessive ice loads during freeze protection may have reduced yields and masked treatment effects. Emerald canopy volume measured in February 2010 showed a rate x type interaction. For AS, canopy volume increase was curvilinear with increasing N rate. For SCU there was no effect of N rate on canopy volume. Jewel canopy volume was not affected by fertilizer rate or type.