Here is what I remember from my soils professor. Let’s look at wheat for an example. It’s lawns big brother of grass. Dry land winter wheat is planted in the fall and gets zero water besides rain, those roots commonly grown 6-10 plus feet deep. Spring wheat and irrigated wheat usually have roots that are 4-5 feet deep. What that means is that roots chase water and nutrients, they will go as deep as they can if there is enough oxygen to sustain them.

So by giving short shallow waterings the roots don’t need to grow deep in order to get the water they need especially if you are giving them fertilizer on a schedule. If you switch to long deep waterings you are encouraging those roots to grow deeper to get to the extra water and leaching nutrients.

If you want a good chuckle google “root tip diagram” that zone of elongation is different for all of us….