310 Lowbush Blueberry Response to Soil- or Foliar-applied Zinc Fertilizers

Abstract

Lowbush blueberries (Vaccinium angustifolium Ait.) in two commercial fields were treated with a preemergent soil application of ZnSO4 at 0.34 g Zn/m2 or a prune-year or crop-year foliar application of Zintrac (1.76 g Zn/L) in a RCB design with five treatments and nine blocks, using 1.5 x 15-m treatment plots. Prune-year foliar Zintrac treatments were applied 20 June and 30 June at 53.8 mL·m-2 or 20 June at 107.6 mL·m-2. A crop-year application of Zintrac at 53.8 mL·m-2 was made on 26 June at only one location. Composite leaf tissue samples taken 14 July of the prune year indicated that two applications of Zintrac at 53.8 mL·m-2 raised Zn concentrations at both locations more than a single application at twice the rate. Soil application of ZnSO4 did not raise leaf Zn concentrations compared to the control at either location. Crop-year leaf samples taken 6 July at the site that received the crop-year foliar treatment indicated no carryover effect of prune-year Zn treatments on leaf Zn concentration, but crop-year foliar application of Zn from Zintrac did raise leaf Zn concentrations compared to the controls. The characteristics of stems sampled in the fall of the prune year at each location (stem density, stem length, flower bud formation) were not meaningfully affected by any of the prune-year treatments. Blueberry yield was not affected by any of the treatments at either location. These data suggest that control plot leaf Zn concentrations of about 15 ppm in both fields were adequate. Raising the leaf Zn concentrations to about 80 ppm with two applications of Zintrac at 53.8 mL·m -2 had no effect on growth or yield.