Calcium usually is added to soils in large quantities via agricultural limestone, or contained at soil clay adsorption sites or in clay mineral composition. Some of this calcium may be fixed by soils or lost through leaching, but a large amount should be readily available to crops. 40 percent Ca and 60 percent carbonate. Given the high amounts of calcium, especially in a diagonal running northeast from Ripley County through southern Scott County, it is reasonable to expect that irrigation water is supplying appreciable agricultural limestone value to irrigated fields in Southeast Missouri. Irrigators should soil test routinely to identify agricultural limestone needs.
Magnesium deficiencies are rare in the Midwest.
As discussed with calcium, magnesium in combination with carbonate will represent some agricultural limestone equivalent. In general, magnesium concentrations in irrigation samples were one-tenth those of calcium. Still, if small areas in fields are magnesium-deficient, then irrigation will supply some magnesium crop needs. However, deficiencies of these micro-nutrients are rarely reported in Southeast Missouri. Also, these nutrients commonly form precipitate minerals in water or soils.