Correcting Lowbush Blueberry Boron Deficiency with Soil or Foliar Application

in HortScience
View More View Less
  • 1 Horticulture Program, Univ. of Maine, Orono, ME 04469

In the acid podzol soils of Maine where most lowbush blueberries are grown, low availability of boron tends to keep foliar B concentration below the 24 ppm standard. To compare efficacy of soil and foliar boron application methods, 1.5 × 7.6-m treatment plots in a commer-cial lowbush blueberry field received soil-applied borate at 0, 1.1, 2.2, or 3.3 kg·ha-1 B with or without additional DAP (89 kg·ha-1 P) and ZnSO4 (3.3 kg·ha-1 Zn) or foliar-applied Solubor at 0, 0.24, 0.49, or 0.74 kg·ha-1 B with or without the additional DAP and Zn. These 16 treatments were replicated eight times in a randomized complete-block design. Leaf B concentrations were raised by all soil-applied borate treatments and by the 0.49 and 0.74 kg·ha-1 B foliar Solubor treatments, compared to the controls. When borate at 2.2 or 3.3 kg·ha-1 B was combined with DAP plus Zn a lower leaf B concentration was observed compared to B alone, possibly due to a dilution effect caused by an increase in DAP-induced growth. Leaf P deficiency (<0.125% P) was corrected when DAP and Zn were included in the fertilizer treatment. The greatest potential yield (flower buds/stem and flower bud density) was measured in treatment plots receiving a combination of DAP plus Zn and either borate at 2.2 kg·ha-1 B or Solubor at 0.74 kg·ha-1 B. With no additional treatments applied in 1999, leaf B concentrations were slightly higher in soil-treated and foliar-treated plots than in controls suggesting a small carryover from 1997-applied boron. Carryover may vary with rainfall.