Elemental sulphur must be oxidized by soil microbes to SO4-S before it is available to crops. Thus, it takes considerably more time for S° to become available compared to soluble sulphate forms of fertilizer. The rate of conversion from Sø to plant available SO4-S mainly depends on the particle size to which the product degrades and the method of application. Research has determined that S° granules that break down into particles smaller than 150 Microns (10-6 m) convert quickly, since particles of this size (and smaller) provide sufficient surface area for microbes to act on. After two simulated wet/freeze cycles and one rainfall, SulFer 95 (0-0-0-95) are all <74 microns whereas only 25 per cent of Tiger 90 particles were <150 microns.
The evolution of elemental S° products is rapid. Some of the products available at the time of this publication include Tiger 90cr, SulFer 95, Montana 90, Keg River 85 and Brimstone 90. Industry is continually striving to improve the dispersing nature of their S° products, making it difficult to give current comparisons between various S° products.
Regardless of brand, all S° products should be surface broadcast without immediate (or no) incorporation for at least a year before the crop. Elemental sulphur sitting on the soil surface is more easily oxidized by soil microbes because rainfall and freeze/thaw cycles break down and disperse the granules.
Banding or immediate incorporation is an inefficient method of applying S°. The surrounding soil keeps the S° granule intact, reducing the exposed S° surface area and vastly reducing the conversion rate to SO4-S. Even with broadcast applications, the rate of conversion from S°to SO4-S can vary from less than a year to several years or more.
One research study showed that surface applied applications after seeding of the S° product SulFer 95 produced yields similar to 20-0-0-24 (Table 2). By contrast, another study demonstrated that on sandy dry soils, the rate of conversion of S° can be much slower. Canola yields were found to be significantly greater when fertilized with a spring banded application of ammonium sulphate (20-0-0-24) compared to spring or even fall broadcast Tiger 90 or SulFer 95 (Table 3, Figure 8). In both studies, surface applied applications of Tiger 90 produced lower yields compared to SulFer 95, indicating a slower conversion rate.
Application of 30 pounds per acre is suggested, but read your packaging materials, and get a soil test.