Magnesium is one of trace minerals which are mobile within the plant. Magnesium is the critical core of the chlorophyll molecule in plant tissue. If deficient in magnesium, plants have poor and stunted plant growth. Magnesium helps to activate enzyme systems, which build, modify or create various compounds as part of the plants normal metabolism.
Magnesium deficiency typically occurs in acidic soils (pH below 5.5), but can be alleviated with the use of dolomitic limestone. Deficiency signs in corn are the loss of healthy green color with striping the full length of the leaf. Soybeans show deficiency by the loss of green color in the lower leaves.
Grains take a large amount of magnesium out of the soil during a complete growing cycle. A 200 bushel corn crop will utilize 50 lbs. /acre of magnesium. A 60 bu. /acre soybean crop will utilize 25-30 lbs. /acre of magnesium. If there is a deficiency during the growing period it will reduce corn yield by 5-15 bu. /acre and soybean yield will be reduced by 3-10 bu. /acre.
Magnesium also influences the earliness and uniform maturity of the crop. This is a greater factor in soybeans. Magnesium sulfate is used to provide magnesium to the plants and the sulfate portion contributes sulfur to the plant which is becoming a more deficient nutrient.