With the increase in both crop prices and fertilizer, it can become very tempting to cut costs while still hoping to achieve maximum yields. The fertility required for a 2,000-pound canola crop (combining residual soil fertility identified through soil tests and applied fertilizer) includes 130 pounds of nitrogen, 50 pounds of phosphorus, 100 pounds of potassium and 30 pounds of sulfur.
Data from the 2006 Minot Answer Plot® location showed a positive net return after an additional expense of $11.50 per acre.* This was achieved with an application of 130 pounds of 11-52-0 (50 pounds starter plus 80 pounds early broadcast) on soil testing high for phosphorus. Calculations included $700 per ton for 11-52-0 and 25 cents per pound for canola. Data from North Dakota State University (NDSU) in 2005 showed good responses on fields testing both low and high for phosphate.
*Because of factors outside of Winfield Solutions’ control, results to be obtained, including but not limited to yields, financial performance, profits, losses or otherwise, cannot be predicted or guaranteed by Winfield Solutions, LLC.
An important fertility requirement for canola is sulfur, with ammonium sulfate as the highly preferred source. This nutrient is as important for canola as any of the big three fertility types: nitrogen, phosphorus and potassium. Low sulfur amounts pose a very serious threat in canola production. Having the right amount available to the crop can mean the difference of producing a great yield or having a disastrous year. With heavy spring rains, many fields have shown an impressive net return from a top-dressed application of sulfur and nitrogen.
Canola takes up sulfur in the sulfate form, so using readily available forms such as ammonium sulfate and ammonium thiosulfate are highly recommended. Trials in Canada and North Dakota have demonstrated that the use of these sulfate forms delivers the best net economic response in raising canola. Spring applications of sulfate usually provide the greatest amounts available for that growing season.
Elemental sulfur has a lower solubility, so it needs to break down and become available to the crop. Elemental forms are not recommended unless the full amount needed is being met by the sulfate form alone and not part of a blend that meets total crop needs.
Sulfur is considerably variable in fields due to organic matter content and soil texture. Hilltops and slopes, along with areas containing more sand or silt, will have lower levels than other more productive areas. A few cores with high sulfur content included in a composite sample can mask the overall field variance.
When a sample gets sent into a lab, the soil is heated and dried. This can cause artificial elevation of sulfur levels in the sample, and, in combination with field variability, often falsely results in fields showing little or no need of sulfur. Soil testing for this nutrient is not as reliable as the tests for nitrogen, phosphorus or potassium. Due to the high sulfur demand by the crop and the unreliability of soil tests, sulfur applications are recommended, even if soil tests report high levels of sulfur.
To make sure you provide adequate sulfur to canola, applying 20 to 30 pounds of actual sulfur in the sulfate form is highly recommended. While it’s tempting to apply sulfur at the time of seeding to save application costs, caution is advised since canola is very sensitive to fertilizer salts. Some sulfur can be applied with phosphate at seeding if the soil texture, row spacing and seed spread will not lead to seed injury. We also need to be mindful of the total amount of nitrogen and potassium near the seed. Broadcasting ammonium sulfate prior to seeding is the safest.
Sulfur in the sulfate form can be leached through the soil profile, especially with lighter soil textures. If early-season deficiency symptoms show up, it is important to take action. Canola yield is often impacted if no sulfur treatment is made. It is best to top-dress with sulfate sulfur as early as possible so that rain can move the fertilizer down into the roots where uptake can correct the issue.
This rescue treatment can be made by applying ammonium sulfate or ammonium thiosulfate. A dry ammonium sulfate application is best done when canola leaves are dry. A liquid ammonium thiosulfate should be applied after the fifth leaf stage to minimize leaf burn that can occur due to the waxy leaf surface. Top-dressing canola after flowering starts does not generally show an economic response. A 60-pound-per-acre ammonium sulfate application can deliver a successful sulfur rescue treatment.
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Sulfur deficiency is evident on this two-leaf stage canola plant. Notice the cupping and blotchy-yellow and light-green color of the first two true leaves. The new, tiny third leaf is a purplish color.
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A close-up look at this five-leaf canola plant from a loam soil field provides a detailed view of the second leaf’s blotchy-yellow and light-green color, which indicates sulfur deficiency.
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