Effects of stoichiometric ratio fertilization on leaf photosynthetic characteristics and fruit quality of blueberry

This study aims to accurately determine the fertilizer demand of blueberries during different developmental stages. The ecological stoichiometry of C, N, P, and K in plant leaves is an important indicator of plant's ability to absorb and utilize its nutrient elements as well as mineral elements in soils. This work experimentally measured the theoretical NPK fertilizer requirement of seven-year-old rabbiteye blueberry 'Powderblue' according to their ecological stoichiometric ratios in leaves, along with photosynthetic rates and area. Calculations were obtained every ten days during flowering stage (S1), fruit setting stage (S2), young fruit stage (S3) and fruit expanding stage (S4). Different N, P, and K fertilizer gradients (1F, 5F, 10F, and 15F) were evaluated at four developmental stages to verify the fertilizer requirement of blueberry. The experimental observations were used to examine the effects of various NPK fertilizer amounts across growth stages on the photosynthetic characteristics of blueberry leaves as well as fruit yield and quality. Fertilization significantly enhanced the plants' photosynthetic capacity. S1-5F, S2-10F, S3-15F, and S4-1F treatments largely increased the longitudinal and transverse diameters of fruits and the single fruit weight. Higher fertilization levels (15F) during each stage facilitated anthocyanin synthesis and increased soluble protein content. Stoichiometric analysis revealed that blueberry during the flowering, fruit setting, young fruit, and fruit expansion periods required 4.85, 5.89, 3.21, and 12.63 g of N, 0.17, 0.18, 0.18, and 0.40 g of P, and 3.54, 3.24, 3.32, and 5.28 g of K, respectively. These nutrients were sourced from 22.88, 27.81, 15.13, and 59.60 g/plant of ammonium sulfate, 0.67, 0.72, 0.71, and 1.61 g/plant of superphosphate, and 7.90, 7.25, 7.43, and 11.80 g/plant of potassium sulfate.