Why should nitrogen get all the buzz?

A successful canola crop needs a lot of nitrogen, which is why nitrogen earns A-list buzz. That same successful crop also depends on a strong supporting cast – phosphorus, potassium, sulphur and micronutrients.

University of Saskatchewan researchers recently updated the nutrient uptake and removal guidelines for 14 annual crops grown in Western Canada. The researchers, in doing their surveys, discovered considerable variability in uptake and removal due in part to differences in weather and management, which is why they say these numbers are guidelines only, not prescriptions. 

Farmers will benefit from soil tests, yield history and economics to determine how much fertilizer their canola needs.

Nitrogen

The 2023 guidelines put average nitrogen uptake for canola at 2.38 pounds per bushel, with a wide range of 1.12 to 3.64.

A 50 bu./ac. canola crop will need 119 lb./ac. of nitrogen, based on the guideline average. Some of that will come from soil nitrate reserves and mineralization of soil organic matter. Soil test analysis will recommend a fertilizer rate based on target yield and soil nitrate levels. Nitrogen from mineralization is difficult to estimate and is not included.

Phosphorus

Many fields on the Prairies test low or very low for available phosphate. The new uptake and removal guidelines put average phosphate uptake for canola at 0.90 lb./bu., with a range from 0.40 to 1.30. Based on the average, a 50 bu./ac. canola crop will need 45 lb./ac. of available phosphate.

Farms can safely place up to 20 lb./ac. of phosphate in the seed row for an early pop-up benefit – as long as soils have decent moisture. With dry soils, any fertilizer in the seed row will put seed at risk of fertilizer damage. Additional phosphate could go into the side or mid-row band with the rest of the fertilizer.

Sulphur

The new guidelines say canola takes up 0.86 pounds of sulphur per bushel of yield, on average, making it a high sulphur-using crop. A 50 bu./ac. canola crop needs 43 lb./ac. of sulphur, on average.

If soil tests are low in sulphur, fertilize according to soil test recommendations. If soil is moderate or high in sulphur, a small amount, say 10-15 lb./ac., may be required to offset the high variability in sulphur levels across a field.

New research from Raju Soolanayakanahally with Agriculture and Agri-Food Canada in Saskatoon showed that canola with adequate sulphur fertilizer may be more tolerant of water deficit conditions. This is another reason to make sure canola has enough sulphur.

Potassium

Canola plants need 2.93 pounds of potassium (K2O) for every bushel of seed yield, according to the new guidelines. A 50 bu./ac. crop can take up 147 lb./ac. of potassium, on average.

Because most potassium returns to the soil through residue and because “young” Prairie soils generally have higher potassium levels, canola crops do not often show a response to potassium fertilizer. But if soil tests show less than 250 pounds per acre (125 ppm), canola may benefit from a potassium application.

Fertilizer rates are a moving target and the “right rate” can vary considerably field to field. We encourage farmers to use soil tests. Use the recommended rates – which are set based on yield projection, soil nitrate reserves and mineralization potential of each soil – as a guide to set an appropriate rate for each field.

 

**The final report for the University of Saskatchewan study, “Revising the crop nutrient uptake and removal guidelines for Western Canada,” is available through the Canola Research Hub at canolaresearch.ca. Search for the study name, then click “SaskCanola final report” in the black box at the bottom. Check tables 3, 4, 5 and 6.

The new Prairie Nutrient Removal Calculator at prairienutrientcalculator.info is based on numbers from the 2023 updated guidelines. The calculator includes data for all 14 crops as well as micronutrients boron, copper and zinc. Note, the calculator only provides removal, not uptake.

To hear Glenda-Lee's conversation with  Agronomy SpecialistWarren Ward click on the link below.