Properly Timed Foliar Nutrient Applications Provide an Efficient Means to Meet Nutrient Demand to Increase Flowering, Fruit Set, and Size of Citrus and Avocado

Abstract

The goal of our research is to identify the role that specific essential nutrient elements play in the physiology of horticultural crops and then to apply the nutrient as a fertilizer to the foliage at key times in the phenology of the tree, i.e., a time when the demand for the nutrient is likely to be high, in order to stimulate a specific physiological process. This approach proved successful in the following completed studies. A single winter prebloom application of nitrogen as low-biuret urea made to the foliage of 30-year-old `Washington' navel orange (Citrus sinensis L. Osbeck) trees at the time of irreversible commitment to flowering significantly increased yield and fruit number per tree for each of three consecutive years. In addition, the number of commercially valuable fruit with diameters of 6.1 to 8.0 cm significantly increased as yield increased (r2=0.88). Applications of boron as sodium tetraborate to the foliage of a commercial orchard of `Hass' avocado (Persea americana Mill.) trees at the cauliflower stage of inflorescence development (gametogenesis) increased the number of pollen tubes reaching the ovule, ovule viability and cumulative yield (P ≤ 0.05). Additional examples from ongoing research also will be presented.