In other cases, calcium may override magnesium and cause a deficiency. If present in excess, magnesium may also create a problem by starving the plant for calcium.
In areas where limestone is high in calcium and lacking in magnesium, it may pay to use finishing lime from a building-material yard to supply magnesium. A light dusting of finishing lime on the soil every second or third year should be enough, unless fertilizers high in sulfates have been used. In this case, an annual application
of finishing lime may be needed to replace magnesium washed out as Epsom salts (magnesium sulfate). Epsom salts are highly soluble and readily washed out of soil.
Calcium is a vital plant nutrient, particularly during early growth. It is needed to form cell walls and to serve as a building block in protein. As might be guessed from its role in neutralizing soil acids, it also helps tame acids formed during growth which might otherwise harm plant tissues.
Magnesium, an essential element in chlorophyll formation, has been exhausted from many older cultivated soils. Overliming with calcium, without also adding magnesium, may hinder chlorophyll formation in plants. To check whether magnesium is needed, mix a tablespoonful of Epsom salts to a quart of water and spray it on some foliage. If the leaves turn a darker green, a shortage of magnesium in the soil is indicated. A dusting of finishing lime between the plants (avoid hitting foliage and stems) will be of benefit.
Sulfur is seldom mentioned in discussions of plant nutrition and is never listed as an essential ingredient on fertilizer bags. It may surprise you to learn that plants utilize sulfur as much as or more than they do phosphorus. For example, while a crop of cabbage may use up only 25 pounds of phosphorus per acre, it will extract 40 to SO pounds of sulfur.
During the latter part of the nineteenth century, scientists believed that sulfur was not an essential plant nutrient. During that period, all analyses for essential elements were made by burning plant tissues and analyzing the ash. Since sulfur is volatile at ashing temperatures, it went out the flue and did not appear in the residue.
I was fortunate in being able to study under the great Cyril G. Hopkins during the last years of his life. It was he who pointed out that sulfur probably is washed down out of the atmosphere by rain and snow in much the same way as nitrogen oxides are precipitated. He predicted that no sulfur shortages would occur in areas where fumes from factory chimneys were belching this element into the air in quantities sufficient for normal growth.