Does It Pay to Fertigate Apples

This is not an easy question to answer and until recently it would have stumped most knowledgeable horticulturists. In some ways, the answer would almost seem like a slam-dunk. We want a reliable supply of both nutrients and water through the growing season to make sure there are no deficiencies of anything getting to the roots.

So really, the apparent simple answer is to dissolve the nutrients into a bulk tank and meter them off as needed by way of a solid set irrigation system (Figure 1). Thereby providing both water and nutrients. This type of technology was developed in arid climate countries like California and Israel. Some years it’s almost semi arid in Ontario with unreliable rainfall patterns while other years bring more rain than we can use.

With the advancements in both irrigation technology and fertilizer technology in the last decade, it is possible to combine both water and nutrients and deliver them uniformly to the rootsystem of apples in high-density plantings. Researchers at Cornell (Terence Robinson and Warren Stiles) have studied this concept and drawn some conclusions.

We know how important it is to water young trees. These New York researchers have concluded that the use of ground fertilizers is best where some form of irrigation is used to get the fertilizer materials mobilized and working. Average fruit size on young trees was in most cases improved with trickle irrigation plus ground applied fertilizers or fertigation.

What the researchers found on young trees was that the distinction between fertigated trees and trees receiving water plus ground applied fertilizers was not consistent on typical orchard soils in the State of New York.

On older trees, the method of application of potassium either through the trickle line or on the ground made no difference. The trickle treatments however did move nutrients much deeper into the soil profile than did the ground applied treatments. The depth of penetration of potassium with fertigation was up to 2 feet or 60 cm. Ground applied materials could only be found at a maximum depth of 16 inches or 40 cm.

They did comment on timing of irrigation and like we have seen here in Ontario it’s not wise to wait too long to get started with water applications even as early as June 1 in an average year. This year of course we could have sold water if anyone needed it.

With fertigation treatments in wet years, both Robinson and Stiles recommend using only enough water to get the fertilizer on while in dry years the objective would be to use enough water to replace what has been lost by the trees. The 2 nutrients most commonly applied through trickle technology are Nitrogen and Potassium. Magnesium and Boron can be applied through methods of fertigation or foliarly. Zinc and Calcium are best applied foliarly.

Figure 1. High density planting of apple showing trickle line with pressure compensating emitters.