Nutrients can be absorbed by plants either through roots or leaves.
The primary route for nutrient absorption is through roots.
For nutrients such as nitrogen and potassium, foliar application alone cannot be sufficient without soil application.
The small quantities of micronutrients such as zinc, iron, boron, manganese used, are good candidates for foliar application in situations where nutrient supply through soil is limited due to high pH.
On the other hand, some micronutrients such as boron or calcium, are not mobile in plants and therefore must be applied foliarly in order to be delivered to needed plant parts.
Postharvest foliar application
Postharvest foliar application of nutrients is a common practice in fruit production. This type of fertiliser application is often beneficial as it ensures adequate nutrient storage for the following spring.
At the end of the season trees are exhausted and uptake by roots is slow, therefore essential micronutrients must be applied to leaves so nutrient status can be enhanced for the spring flowering period.
Differences between cultivars
There are differences in leaf physiology between cultivars postharvest.
Early season varieties of fruit can experience a substantial period of full postharvest leaf function, while late species and varieties have very little active postharvest leaf function.
Therefore, postharvest treatments will have best efficacy if applied right after picking.
Fertilisers for postharvest application
Some foliar fertilisers for postharvest application have certain amounts of nitrogen in their formulation.
Considering that the nitrogen is usually withheld from a tree to reduce vigour or to develop colour in fruit, leaf nitrogen application after harvest can be enough to supply the fruit buds for spring growth and activate metabolism of micronutrients applied.
(continued next month)
See this article and photos in Tree Fruit March 2017
