Features Fertilizer Seed & Chemical
Canola seeking sulphur

Canola loves sulphur, and many Ontario growers have been including sulphur as part of their standard fertilizer blends for years. Matched only by alfalfa in uptake, a canola crop can demand anywhere from 25 to 28 pounds per acre of sulphur annually. Interestingly enough, for years, a significant portion of sulphur was provided environmentally. Brian Hall, the edible bean and canola specialist for the Ontario Ministry of Agriculture and Food (OMAF), says less acid rain has been good for the environment in general and human health, but perhaps not so good for canola and growers.

“Back in the early ’90s, we were getting upwards of 20 pounds of sulphur deposited per acre annually, and now we’re below 10 pounds,” Hall explains. “Over the last number of years, we find growers who have increasing sulphur deficiency in canola on sandy soils, dry areas and side slopes of fields.”

Though he isn’t exactly sure the changes in acid rain explain everything, Hall has worked with a number of co-operators, including Bonnie Ball, a soil fertility specialist with OMAF and MRA, and Jeff Holmes of Holmes Agro, to respond to the emerging issue. Results from a three-year study, conducted by growers on their own farms in field-length replicated strips, were released last fall. The results demonstrated significant responses to sulphur application across most sites.

Last year, Hall’s team began to work on defining application rates of sulphur. He says in Western Canada, the recommended range lies between 15 and 20 pounds per acre. In Ontario, however, some growers have insisted the rate needs to be closer to 40 pounds. While excessive most years, the growers’ perspective was that the money spent unnecessarily most years made up for the extra cost in high-risk years because the ability to correct a post-symptomatic sulphur deficiency is extremely limited – at least, until the cost of sulphur increased so much.

“We used to get very competitive sulphur, whereas now it just seems to get gobbled up so quickly . . . and they know now there’s a demand for it now,” notes Holmes, adding that ArcelorMittal Dofasco, a steel company based in Hamilton, Ont., used to sell ammonium sulphate as a byproduct. But that changed when anything tied to nitrogen started shooting up in value and the demand for sulphur in the phosphate fertilizer business increased too. The agronomist has been promoting a nitrogen:sulphur ratio program, according to soil type and test results, on high-end nitrogen-use crops because he’s found growers can save up to 10 per cent of their nitrogen with the right application of sulphur. Holmes thinks using different sulphur sources also helps, and he’s finding these economical contributions really come into play more than they used to.

“The concern I had was that [growers] were putting a pile of nitrogen on, and I think we’ve been wasting a lot of it,” he says. “All nitrogen is probably being applied more properly than it ever has been, making sure we get the best bang for it.”

Like nitrogen, sulphur is very mobile in the soil. It has a very weak holding capacity, maybe even worse than nitrogen, Holmes suggests. Ball, the field crops soil fertility specialist, explains this as a result of both being easily mineralized by organic matter; and in the same manner that nitrate testing can be tricky, soil testing for sulphur is as well.

“If the test is super high, it’s easy to know that there’s enough there, but when it gets down into the range where it may or may not respond, it takes a bit of interpretation,” says Ball. “It can depend on temperature, when you took the sample, and how deep you sampled.”

Currently, a sample depth of one foot is widely recommended, but Ball says going deeper by an extra foot offers additional information. In the spring, however, under the right circumstances, perhaps six inches would be deep enough. With inconsistency like this, both Ball and Hall are working towards alternative predictive tests for sulphur. Hall says he only has one year’s data so far, and he never puts much stock in results until they’ve tested true over multiple years. But, he notes, one alternative showing promise was plant tissue testing.

“Traditionally, the time for tissue testing was at early flower, [but] at that stage it’s not useful as a predictive tool for helping growers correct an issue,” Hall says. “Collecting whole plant samples at the rosette stage, we saw a pretty good indicator that perhaps plant tissue testing might be useful for predicting the need for sulphur.”

Ball says she also found this in established alfalfa crops where she took tissue samples at the late bud to early bloom stage, testing the top six inches of at least 20 plants over the area in question. Adding elemental sulphur in the fall not only increases crop sulphur content the following year, but also improves yields. She agrees with Hall that more testing is necessary to confirm some of their initial findings.