When is too late for fertigation on crops? What is the difference in yield potential for growers?

Potassium or Potash is considered a Macro nutrient with Sulfur and Magnesium being Secondary nutrients. Zinc and Boron and Manganese among others are the Micronutrients.

Nitro-Mag is not only compatible with added biological products; it is biochemically supportive of the core processes that make biologicals work.