There has been much discussion recently about sulfur fertilization. Increased yields have been one of the major factors increasing the need for sulfur fertilization.
A field that produced 100 bushels per acre in 1970 would average better than 180 bushels per acre in 2009. A 200 bushel per acre corn crop would require 32 lbs/ac of sulfur.
Another factor is the total amount of wet and dry sulfur deposition onto our fields has decreased by 25 to 50 percent between 1990 and 2008 as estimated by the EPA. This has resulted in the reduction of available sulfur.
Also, plants can only utilize sulfur when it is present in the sulfate form. Elemental sulfur, organic sulfur and other non-sulfate compounds must be converted to sulfate prior to becoming plant-available. In the past 150 years, crop production practices, especially high tillage situations, have resulted in soil organic matter levels being lowered by approximately 50 percent in turn reducing the soils sulfur holding capacity.
Better manufacturing practices have also resulted in lowering the sulfur applied to fields. Many early pesticides were applied at high rates per acre and contained significant amounts of sulfur. Sulfuric acid is the material used to dissolve rock phosphate in making phosphorous fertilizer. During the early years, a fair amount of sulfur remained as an impurity in the final fertilizer product.
Sulfur and nitrogen both are necessary for the production of amino acids and proteins in the plant. They both exhibit stunted growth and pale green to yellow appearance. However they do behave differently in the plant.
Nitrogen is a mobile element and if the plants are deficient, the plant will take the nitrogen from the older tissue and move it to the younger tissue. Sulfur is non-mobile and is held in older leaves resulting in the younger leaves expressing the deficiency symptoms first.
There is a soil test that measures plant available soil sulfate. Sulfur fertilization is becoming more of a factor for optimum crop production. Monitor confirmed sulfur problems for a short time as symptoms may lessen as plant root activity increases. There are several fertilizers available that can be applied depending on your management situation.
If crop sulfur issues are suspected, confirm with plant sampling and continue field monitoring. Be prepared to address sulfur more in coming years if tillage decreases soil organic matter, air becomes cleaner, and non-sulfur fertilizer material use continues.