More reasons for soil testing
Ron Goldy, Michigan State University Extension - March 11, 2016
<refer to chart with red and green arrows>
A lesser known but equally important interaction is the one shown by the Mulder’s Chart (Figure 2). The Mulder’s chart represents the interaction between 11 of the essential plant elements. Some interactions are positive (synergistic) and others are negative (antagonistic). A synergistic relationship is one where the elements involved help each other by aiding uptake or utilization. In contrast, an antagonistic relationship means the elements hinder each other in uptake or utilization. For example, adequate potassium aids in use of iron and manganese, but if it is too high it will hinder (antagonizes) utilization of magnesium, boron, nitrogen, phosphorous and calcium. An antagonized element may be present in adequate levels, but there is so much potassium present the plant doesn’t have access to it. Elements that act as antagonists can do so in a couple ways. If calcium is in excess it can simply out-compete other elements such as potassium and magnesium for uptake sites on the roots, or it can change soil chemistry by elevating pH to the point iron and boron become unavailable
Really, I don't mind learning, as long as it doesn't hurt!!! 
. And, the recommendation rarely comes with why Calcium is the answer to the problem; just "Calcium and we need more photos".
