NEWS for North Dakotans
Agriculture Communication, North Dakota
State University
7 Morrill Hall, Fargo, ND 58105-5665
March 26, 1998
Low soil sulfur levels can hurt canola more than any other crop normally grown in North Dakota, which is why growers should take care to apply sulfur in a form that will do the most good, according to Dave Franzen, soil specialist for the North Dakota State University Extension Service.
"Generally a sulfate-based fertilizer, such as ammonium sulfate—or else a fertilizer that soil processes can rapidly convert to a sulfate, such as ammonium thiosulfate—are best in North Dakota," says Franzen. "These fertilizers are able to quickly provide sulfur to the canola plants."
Much less efficient, he says, are the various forms of elemental sulfur, which must go through a two-step process before their sulfur becomes useful to plants: the elemental sulfur granule must be broken down into dust-size particles, then transformed by soil bacteria into sulfate.
Because the breakdown of pure elemental sulfur granules into particles is very slow, elemental sulfurs are sometimes blended with bentonite clay, says Franzen. The clay in such blends absorbs moisture, swells and breaks the sulfur granules apart—provided sufficient water is available.
Once broken into particles, the bacteria can go to work. But transformation by bacteria can be a very slow process, depending on soil moisture, temperature and pH. In one study, says Franzen, two months elapsed before half the elemental sulfur was transformed to a sulfate that the plants could use.
"The elemental sulfurs do have many practical advantages," says Franzen, "but getting to the plant quickly is not one of them. Among the advantages are a high concentration of sulfur, small storage space requirements and smaller transportation costs per unit of sulfur. Also, relatively large amounts can be placed with the seed at planting. But plants cannot use elemental sulfur directly, which is why getting enough plant-available sulfur out of elemental sulfur—and getting it when it's needed—is often a problem."
In one study, near Rock Lake, N.D., 20 pounds per acre of sulfur as ammonium sulfate was applied to certain hilltops, side slopes and toe slopes, while 40 pounds per acre of sulfur as elemental sulfur formulated with bentonite clay was applied to other hilltops, side slopes and toe slopes. Canola fertilized with ammonium sulfate yielded 1,810 pounds per acre on hilltops, while canola fertilized with elemental sulfur yielded only 1,260. On side slopes the figure was 1,980 pounds for the ammonium sulfate fields, 1,290 for the elemental sulfate fields. On toe slopes the yields were 1,860 pounds with ammonium sulfate, 1,470 pounds with elemental sulfur.
"Applying ammonium sulfate may change the fertilizer strategy for some producers," says Franzen, "since canola is very sensitive to seed-placed fertilizer. In many fields, broadcast application of ammonium sulfate may be required."
For more information, contact any county office of the NDSU Extension Service and ask for extension publication SF-1122, "Fertilizing Mustard and Canola," which provides information on the amount of fertilizer allowable with the canola seed, color pictures of sulfur deficiency symptoms at different stages of growth, and other useful canola fertility information.
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Source: Dave Franzen (701) 231-8884
Editor: Barry Brissman (701) 231-7866