Use of potassium is less complex than nitrogen use, but is still a significant issue.

K uptake comes from fertilization as well as organic matter and mineral weathering. Potassium utilization can also be influenced by clay particles in the soil.

Zelinski said if K stays too long in the soil without being taken up by the vines, it becomes fixed to the clay particles. “What I like about drip irrigation is that K can be taken up more readily by the plant by applying water directly to the roots.”

Drip irrigation also plays a role in soil pH which impacts nutrient utilization. Sulfuric acid is often used to keep irrigation lines free from algae and this can dramatically change the soil pH around in the wetted emitter area compared to the rest of the field.

Zelinski said it is important to evaluate a fertilizer application based on:

  • Are nutrients where the roots are?
  • Are nutrients available when vines are able to take it up?
  • Are nutrients in a form available to vines?

It is also critical to evaluate sources of nutrients. They may not always come from applied fertilizer. They could come from bacteria in the soil, microbial fungi or even from irrigation water.