Ask An Agronomist: Top Questions and Answers

Smart Nutrition™ MAP+MST® is a new, homogeneous granular product containing monoammonium phosphate (MAP) and micronized sulfur technology (MST). As with any new product, we understand you may have questions about what it is and how it works. In our first edition of Ask an Agronomist, Dr. Robert Mullen and Dr. Cristie Preston are answering some of the top questions we’ve received to help growers incorporate Smart Nutrition MAP+MST into their nutrient management plans.

Would this product be suitable to place in furrow with winter wheat seed in the fall? Would it supply the wheat with available sulfur needs the following year? I usually apply 100lbs of MAP with seed. Was considering using MST to replace MAP. Want to be sure it won’t leach over winter while also being in an available form the next spring/summer.

You could certainly replace your seed-applied MAP with Smart Nutrition MAP+MST, and the sulfur would not be subjected to leaching (since it is primarily elemental sulfur). My only concern would be late winter/early spring sulfur availability. Our MAP+MST has about 10 percent sulfate (1.5 percent of the 16 percent), so that material would be available (if it did not leach).  We have done some research in the Plains on winter wheat, and we have found the elemental sulfur oxidizes a bit slower due to cool soil temperatures. We do pick up yield compared to no sulfur applied, but it did not perform as well as ammonium sulfate.

How many pounds per acre of MST is safe with the seed on canola?

Seed safety has been a very hot topic in the industry for the last couple of years. Smart Nutrition MAP+MST is a great product that has a low salt index, has a lower nitrogen and ammonium sulfate (AMS) analysis compared to competitive products. Our company still advocates to follow provincial seed safety guidelines. We have seen our trials perform very well compared other products in the seed safety trials, but we do not have our own recommendations for seed safety determined. I would discuss rates and option with your local agronomist/retail for more information.

What percentage of the sulfur component is available in the year of application?

When we look at the results from our field trials, we look to see how yields compare to AMS. Since elemental sulfur has to be oxidized to sulfate to be plant available, comparing to a source of sulfur like AMS where the total sulfur is present as sulfate will allow us to tell if the elemental sulfur is oxidized quick enough. The elemental sulfur in MAP+MST does oxidize quicker than granular elemental sulfur due to smaller particle size and assuming adequate moisture/temperature/aeration, the rate of oxidation should be quick enough to supply sulfur to the plant this growing season.

We have observed some circumstances where the elemental sulfur in MAP+MST was not adequately oxidized and those areas were in canola in some of the cooler regions. Depending on your specific weather patterns (i.e., moisture and temperature), we have recommendations of blending MAP+MST with AMS to complete your sulfur nutrient management plan, which actually works out well for canola production. Areas, say south of highway 80, we have not seen any issues with oxidation rates with yields being similar if not better than AMS.

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