Why nutrient balance is important to plants.

There are many factors that come into play when it comes to availability of nutrients.  Soil tests are good indicators of what nutrients may be lacking in a particular soil or section of a field, however, they are only indicators of the nutrients that are present and cannot discriminate between available nutrients and nutrients that are unavailable to plants.  Farmers generally apply some form of the major nutrients, nitrogen, phosphorus, and potassium (NPK).  When it comes to secondary nutrients (Ca, Mg, S) and micronutrients (B, Cu, Fe, Mn, Zn) farmers usually depend on their soil test to tell them if and what nutrients they need to apply. 

Grid sampling within the Precision Ag concept has had a positive effect on the application of major nutrients but, grid sampling does not work effectively for secondary and micronutrients.  Most secondary and micronutrients are needed in small quantities and the soil test won’t suggest application until a large quantity can be safely recommended without producing toxic effect in the plant. As a result many producers are losing yield because of “hidden hunger” of secondary and micronutrients. Dr. Don Huber, Plant Pathologist of Purdue University describes this circumstance this way, “Plants often can’t draw enough micronutrients from the soil to fend off diseases… these nutrients include manganese, copper, zinc, iron, and boron.  Symptoms are not always apparent. This phenomenon is called, ‘hidden hunger’” (Huber, 2000).

Nutrient balance is a very important aspect of nutrient availability as combinations of nutrients can synergize and/or antagonize uptake of another nutrients both minor and major (Diagram 1).  The addition of a particular nutrient may have a positive or negative effect on the availability of another nutrient.  For example Copper (Cu) has a negative effect on the availability of Zinc (Zn) as well as Zn on Cu.  Iron (Fe) has the same antagonistic relationship with Manganese (Mn).   Calcium (Ca) and Magnesium (Mg) also share an antagonistic relationship.