More farmers adding sulfur to soil

Posted Thursday, February 7, 2013, at 11:33 AM

In the last few years there has been much discussion about using sulfur fertilizer.

More and more producers are using sulfur regularly in their fertility program. Sulfur is critically important in all crops and there are more signs of sulfur deficiency across the country.

Corn and wheat in particular, which require larger amounts of sulfur have shown good yield increases where sulfur has been applied in many instances.

There are several reasons that sulfur is less abundant in our soils than it once was:

1.	Less air pollution -- Partially as a result of less sulfur in emissions, scientists are claiming sulfur deposits in our soils are decreasing by 5 pounds per acre per year.
2.	Less manure application -- There are a lot of good things in manure in addition to nitrogen(N), phosphorous(P), and potassium(K).Sulfur, micronutrients, biological, etc., are big benefits that o0ften go unmentioned in manure applications.
3.	Less availability -- Commonly applied fertilizers used to contain a certain amount of sulfur as a result of the material used and the manufacturing process. Modern manufacturing techniques have eliminated most of the sulfur portion.
4.	More corn acres and less tillage leads to less mineralization (due to cooler soils when covered by residue) and less sulfur release.

One downside to reduced tillage is that more residue leads to cooler soils, which in turn means slower breakdown or mineralization of organic matter. For each 1% of organic matter in your soils, you would typically expect to get two to three pounds of sulfur free each year. With the higher residue levels, the carbon to sulfur ratio becomes important in the mineralization to release the sulfur. If the carbon to sulfur ratio is:

1.	Less than 200 parts carbon to 1 part sulfur = your sulfur will likely be mineralized and made available.
2.	Between 200 to 1 and 400 to 1 = your sulfur will remain in the form it's in until the ratio changes.
3.	3. Greater than 400 parts carbon to 1 part sulfur = your sulfur will be immobilized and unavailable for plant uptake.

The bottom line is that you don't have a lot of mobilization in your soils, nor do you get a lot of sulfur most years from mineralization. Your crops are using quite a bit of sulfur each year and you need to fertilize with enough sulfur to supply each season's crop. Some common crop residue carbons to sulfur ratios are:

Corn residue -- 350 parts carbon to 1 part sulfur

Soybean residue - 125 parts carbon to 1 part sulfur

Wheat residue -- 300 parts carbon to 1 part sulfur

If you have a lot of carbon (corn or wheat residue for example) you may need to apply just a little more sulfur than normal.

Crop Concerns

WAYNE CROOK

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As our local University of Missouri Agronomy Extension Specialist, Crook has been writing a column for the print edition Agriculture page for the past three years and we will now be sharing it on our web version. Crook has a bachelor and masters degree in agronomy from University of Missouri and received his doctorate in Agronomy from Kansas State University. He was in soybean variety development research for 22 years for various seed companies and has been Saline County's agronomy specialist for 10 years.

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