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On Sulfur

February 24, 2011 Leave a comment

Non-ag readers: Geeky agronomy content ahead! You’ve been warned.

Sulfur is an important plant nutrient in all of the crops that we grow: corn, wheat, alfalfa, and even soybeans. Corn, for example, will remove 12 lbs of sulfur for a 180 bushel corn crop. Alfalfa is a very heavy user of sulfur, removing 5lbs of sulfur per ton of alfalfa…that could be 20-40lbs per year, depending on your alfalfa cut schedule and yield. In a nutrient hierarchy, it ranks about 4th in importance, behind nitrogen, phosphorus, and potassium.

Sulfur deposition

Yet, up until recently, I’ve rarely talked about sulfur with my customers. One reason is scale; that same 180 bushel corn crop requires 150-200 lbs of nitrogen, 77lbs of phosphorus, and 50lbs of potassium. We put our focus where the most nutrients where required. Another reason is that for many years, we have to some degree depended on air pollution to provide us with sulfur fertilizer. Coal-fired coal plants used to be prodigious producers of sulfur dioxide, which led to acid rain, which led to sulfur deposition on the soil, and sulfur availability for our crops.

With most coal plants now having scrubbers installed to reduce sulfur dioxide emissions, our ‘free’ source of sulfur fertilizer has diminished. I’ve been seeing a lot of sulfur deficiencies in corn over the last couple of years during certain parts of the growing season. From a distance, it can easily be mistaken for nitrogen deficiency, but when you get up close, the interveinal yellowing is obvious.

Sulfur deficient corn

Luckily, there are many commercially available sources of sulfur that we can apply to our crops. If you are near a large coal plant, as I am, you may even have access to the synthetic gypsum that many power plants generate as a result of their sulfur scrubbing process. Fertilizer grade ammonium sulfate should be readily available at many fertilizer dealerships. You can also get liquid ammonium thiosulfate. I generally recommend avoided elemental sulfur: while it is a high anaylsis (90% sulfur, compared to 24% or 26% for the sulfate products), it has to convert to a sulfate form in the soil in order to be available to the plant. This takes time, and can result in sulfur not being available to your crop when it is needed. Talk to your local agronomist, and see is recommended and available in your area.

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