11/26/2021 - By Dr. Tom Reed

Conclusion:

The study investigated the effects of three planting densities, two Harrell’s controlled release fertilizer (CRF) blends, and four foliar applied micronutrients rates on bearing age (5 to 7-year-old) ‘Ray Ruby’ grapefruit on Kuharske citrange in a split-split-plot design. Fertilizer blends were applied three times per year (February, July, October). Target application rate was 161 lb N/ac (180 kg N/ha). In 2018–19, the fertilizer blend did not affect fruit quality. In 2019–20, a 12-3-14 blend was used with 70% CRN with recommended or increased micronutrient levels. That season CRF 1 with higher micronutrients induced 10% higher soluble solids, 7% higher ratio, and 86% greater yield of solids than CRF 2 as well as increasing photosynthesis (17%) compared with CRF 2. The CRF 1 blend combined with the highest planting density produced greater yield of solids than other treatments with reduced fruit number. Balanced nutrient application can mitigate Huanglongbing (HLB) disease, high-density planting optimizes yield under HLB-endemic conditions, higher micronutrients increased canopy volume and foliar micronutrient application did not enhance yield and excessive supplemental application may increase vegetative growth resulting in reduced yield.

Figure 1: Nutrient rates for Harrell’s CRF blends in study.