Citrus Response to Zinc and Boron Fertilization.

Poor nutrient management is one of the factors contributing to decline citrus fruits production in Pakistan. A study was conducted on 15 farmer’s fields in the Punjab Province of Pakistan (Sargodha and T.T. Singh) to evaluate the impact of Zinc (Zn) and Boron (B) on citrus fruit yields, nutrient uptake and soil properties. The Zn as zinc sulfate (at 0, 50 and 100 g/plant) and B as borax (at 0, 25, and 50 g/plant) were applied in factorial combination to the standing citrus trees in selected farmer’s fields. Standard rates of N, P and K fertilization were applied. At maturity, the fruits were harvested to collect data on total number and weight of marketable fruits and average weight of the fruits. Fully developed new leaves leaf from non-fruiting terminals were randomly collected, oven-dried, ground, and analyzed for total N, P, K, Zn and B concentration. Soil samples were also collected to analyze for pH, electrical conductivity (Ec), soil organic matter (SOM), available phosphorus (AP), and exchangeable potassium (K), Zn, and B. Results showed that Zn and B treatments had significant quadratic effects to improve the total number and weight of marketable fruits, and average fruit weight of citrus. Highest number of fruits (>50%) were found in Zn50-B25 treatment compared to control. Likewise, the total weight of harvested fruits was higher (19%) in Zn50-B25 treatment compared to control. Leaf nutrient uptake such as N, K, and Zn was highest in Zn100-B0 treatment. In contrast, the leaf uptake of P and B was highest in Zn50-B25 and Zn0-B50 treatments, respectively. Soil pH, Ec, SOM, AP, and K did not change consistently. However, soil Zn and B concentration changed in response to Zn and B fertilization. Partitioning of Zn and B treatments for individual nutrient effects justified the non-linear response of both micronutrients on citrus fruit yields and leaf nutrient uptake. Based on our experimental findings, it is recommended that Zn50-B25 fertilization will greatly improve the citrus fruit production in Punjab.