Generally, we recommend 20-25% of the season’s nitrogen budget to be applied in the post harvest period. This is based upon having a Mid-July leaf nitrogen value within the range of 2.2-2.5%. This nitrogen is used for the post-harvest growth processes, which includes both vegetative and fruit bud development and some vegetative growth.
When making this application, the sooner, the better, as it will help reduce tree stress. Studies have shown that ‘Nonpareil’s’ fruit bud differentiates about 7-14 days after harvest, while other varieties, such as ‘Carmel’, the majority of fruit buds differentiate prior to ‘Carmel’ harvest. This timing will be delayed in cool, mild years. Tree stressed imposed during this period will reduce fruit bud set, and the buds will remain vegetative (leaf buds).
In the cases of above recommended mid-July leaf nitrogen levels, nitrogen should still be applied, but the amount should be reduced. For example, if leaf nitrogen values are around 2.8%, apply 15-20% of the total seasonal nitrogen budget. If over 3%, reduce that application further to 10-15% of the total nitrogen budget.
Nitrogen should be applied with caution in the post-harvest period as early rains may leach nitrate in sandier soils. Late fall (Late September, early October) nitrogen applications should also be reduced; the trees ability to pick up nitrogen is decreased due to lower levels of transpiration.