Fertiliser Supply Affects Flower Abundance but Not Floral Nectar Reward in Blueberry

Fertiliser rates applied to blueberry crops may influence the production and quality of floral nectar, the major attractant for pollinators of blueberry. To test this, three complete fertiliser rates in solution (0.66, 0.84, 1.11 dSm −1 ) were irrigated onto potted blueberry ( Vaccinium corymbosum ‘11‐11’), growing in a glasshouse, for 12 months up to peak flowering, and floral nectar was evaluated. The treatments had no effect on nectar mass or mass of sugars per flower, nectar sugar concentrations, or sucrose:hexose ratios. Plant sink‐source was potentially affected. In fertiliser‐limited plants, leaf chlorophyll index was reduced, non‐structural carbohydrates were accumulated in young stems and fewer flowers were potentially a weaker sink for these assimilates. In contrast, their trunk growth was greater than for other treatments, potentially a stronger sink under reduced flowering. Differences in nectar characteristics between collection days, occurred under similar temperature, humidity and vapour pressure deficit ranges. Potassium (K) (0.078–0.39 mg/L) and phosphorus (P) (<0.01 mg/L) detected in nectar were below those considered repellent to honeybees, but data was limited. Focussing on drivers of nectar variability will assist in evaluating nectar value for pollinators under cultivated conditions. Optimising flower abundance and plant breeding to promote larger flowers in blueberry may improve the floral reward.