There are three plant nutrients that can not be totally supplied to the plant thru foliar applied nutrients. These three are calcium, potassium and phosphate. In our soils in western Oregon, the only one that we have plenty of is potassium. Since our soils are acidic, we are constantly needing to apply calcium carbonate. The carbonate raises the pH and the calcium replaces the hydrogen on the clay colloid.
Phosphate, on the other hand, gets bound almost as soon as it becomes plant available. The amounts of iron and aluminum tie up the phosphate into non-plant available forms.
We have developed a product that helps address this problem. It is Free pHos 24, a product that keeps the phosphate free for plant uptake. For more information on this product, please visit our FreepHos 24 page.