Deep root fertilization should be used to help rebuild your soil food web, not as a way of pumping nutrients into the soil.
Why do your trees and shrubs need deep root fertilization to begin with?
After all trees in the forest are just fine without it. They do not need additional nutrients to survive...
The forest has healthy soil. But where there has been development, you will usually find dirt, not healthy soil. Dirt is devoid of life.
Healthy soil is alive! It is full of microbes, beetles, worms, and many other organisms that make up the soil food web. A healthy soil food web helps plants by providing food, water, and protection against harmful pathogens, fungi, and so forth.
If you choose to use deep root fertilization for your trees and shrubs, select a product that rebuilds the soil food web.
Do not select a product based on its percentages of macro or micro nutrients. And definitely do not choose a product because it has lots of nitrogen!
There is no need to pump the soil full of nitrogen, phosphorus, and potassium.
These do not help the soil food web. You may have heard differently. But was it from somebody who wanted to sell you a product? Or somebody who cared about the best interests of your plants and soil ecology?
Pick a formulation that contains no phosphorus because research shows that it often just leaches through the soil and pollutes our water. And use very low nitrogen. Usually a plant cannot use this nitrogen anyway. It often just irritates vital members of the soil food web, like earthworms. If your product has a high salt index, forget it. That does more harm than good.
Choose a product that is full of essential micro-nutrients, beneficial microbes, humates, and organic matter.
These components will help rejuvenate your soil food web, which will provide your trees and shrubs with all the macro and micro nutrients they need to survive. It will also create the perfect soil pH for your plant. A functioning soil food web creates a series of symbiotic relationships with plants that provide all the resources that each member of the relationship needs.
Be discerning about what you put into your soil. Your plants will thank you.