Around 80% of the nitrogen in fruit and leaves in mature trees originates from tree reserves rather than from fertilizer N applied in that growing season. Pre-bloom foliar sprays made in the winter can help increase yields in the following season by increasing fruit number.
Use of potassium - either through foliar or soil application - results in higher fruit numbers and higher yields.
Calcium in the form of calcium nitrate helps boost fruit set and fruit number. Timing is critical, and significant fruit set improvement come from applications made immediately prior to and during flowering. Less than 30mg of calcium in the fruitlet at 5 weeks will lead to increased fruit drop.
Boron deficiency reduces calcium uptake and increases fruit drop. As a result, adequate boron is important to boost calcium uptake.