Fertilizer Planning for Canola
April 25, 2022
Soil test, soil test, soil test!
A canola fertilizer program should be based on yield goals, the 4Rs of nutrient stewardship (right source, right rate, right time, right place), and current soil nutrient levels. The best practice when making fertility plans is to rely on soil test recommendations for fertilizer inputs. If time or conditions do not allow soil testing in the fall, then it can be completed in the spring. Spring soil testing can often be more accurate when following a drought year, such as 2021.
Nitrogen (N) Only about half of the N on a fall soil test result is available to the following year’s crop. Mineralization of N in organic matter will release N to the crop throughout the growing season and it is important to consider when making N fertilization plans. However, mineralization rates can vary widely with soil type and moisture levels and are limited in the early season when soils are cool and wet. Therefore, in-soil banding, and preferably deep banding, of N in the spring or late fall is advised to supply the N needed for early crop growth.1,2 If a broadcast application is the only option, spring is the best time to help minimize losses, and consider using a urease-inhibitor product.
Phosphorus (P) Fertilize according to soil test recommendations. When high rates are needed, side banding of P fertilizer in the spring is safer for the crop than seed-placed P, which can burn canola seedlings.1
Sulfur (S) Soil tests are important for assessing overall S reserves, but S can be highly variable throughout a field; therefore, even if a soil test shows moderate to high levels of S, some additional S might be needed to alleviate localized deficiencies.
For more detailed information on nutrient inputs for canola, refer to the following articles from the Canola Council of Canada: Canola Watch How much fertilizer does canola need? and Choose the right placement for nitrogen and phosphorus fertilizer applications
Fertility management after a challenging growing season
The severe drought in June through July 2021 decimated canola yields, which were down by 40.2% from yields in 2020, despite a larger harvested area due to optimistic spring projections.3 Low yields may leave soil nutrient reserves higher than expected. With some farmers realizing only around half of their expected yields in 2021, the question for the following growing season becomes: What nutrient credits may remain in the soil from last year?
A soil test is particularly important after an “off” year, when typical crop nutrient removal rates are unreliable. If soil tests were not completed last fall, consider testing in early spring. This can help allow for more distribution of previously applied nutrients in the soil and result in more accurate tests after a dry year.
Another option is to estimate nutrient removal based on canola yield. While this method is not ideal, it can be used for nutrient maintenance when a soil test is not available. Important caveats are that crop removal rates vary by variety (for example, high-performance hybrid canola varieties have higher yield potential than open-pollinated traditional varieties at the same applied nutrient rate4), climate/region, and soil type. This method also does not account for losses due to erosion, leaching, etc. Below is a chart with typical nutrient removal rates in western Canada. Refer to crop nutrient removal estimates from your region and last year’s yields to estimate fertilizer inputs.
Table 1. Nutrient removal rates for canola2
Also, keep in mind what the previous crop was on a field intended for canola. Fall soil tests have shown higher year-over-year residual levels of nutrients following one crop versus another. For example, residual N levels in the fall were higher in wheat stubble versus barley stubble on a year-over-year basis.5
Where can I lower input cost and where should I use a full fertilizer rate?
The simple, less-technical approach to lowering fertilizer inputs is to dial down fertilizer rates in typically low-yielding sections of the field, such as hilltops and low-lying areas, particularly after a hot, dry year like 2021 where leaching and crop nutrient removal was likely limited.
The opposite strategy applies to high-yielding areas of the field. Vigorously growing, healthy plants take up more nutrients; therefore, growers may want to increase fertilizer inputs in these field zones. Additionally, average fertilizer rates may not be adequate to keep up with the demand of newer, high-yielding canola hybrids, and over time soil reserves may be depleted if fertility is not targeted to yield potential.
Alternatively, farmers may opt to even out nutrient variation in the field by dialing back fertilizer inputs in high-production areas and increasing it in low-production areas. This helps to synchronize crop growth and maturity in order to simplify fungicide applications and harvest.
How can variable rate technologies help improve nitrogen use efficiency in canola?
Variable rate technologies can help farmers optimize their inputs based on the variation in their field’s yield potential, but with much greater accuracy. With the Climate FieldView™ platform, canola farmers can build different management zones throughout their field based on biomass production maps (called scouting layers in FieldView™). Then, farmers manually set a prescription for N fertilizer depending on what the management zones call for, which is based on their goal, such as maximizing yield potential in their most productive zones or leveling out nutrient variation in the field. Talk to your representative for more information on how FieldView™ can help improve your farming operation’s efficiency.
Sources:
1 Canola Council of Canada. Choose the right placement for nitrogen and phosphorus fertilizer applications. Canola Research Hub. https://www.canolacouncil.org/research-blog/choose-the-right-placement-for-nitrogen-and-phosphorus-fertilizer-applications/.
2 Canola Council of Canada. How much fertilizer does canola need? Canola Watch. https://www.canolacouncil.org/canola-watch/fundamentals/how-much-fertilizer-does-canola-need/.
3 Statistics Canada. 2021. Production of principal field crops, November 2021. https://www150.statcan.gc.ca/n1/daily-quotidien/211203/dq211203b-eng.htm.
4 Karamanos, R.E., Goh, T.B., and Poisson, D.P. 2006. Nitrogen, phosphorus, and sulfur fertility of hybrid canola. Journal of Plant Nutrition. Vol. 28-7. https://www.tandfonline.com/doi/full/10.1081/PLN-200063138?scroll=top&needAccess=true.
5 Agvise Laboratories. https://www.agvise.com/resources/soil-test-summaries/.
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