Three fertilizer tests to lower your risk

Here are three low-cost, low-risk tests to provide valuable new observations on yield potential, major hidden soil nutrient issues and right rates.

  1. Supplemental soil samples from problem areas
  2. High nitrogen strips
  3. Tissue tests

Supplemental soil samples from problem areas

The most common practice is to collect one composite sample per field. An appropriate composite is based on 15-20 sub-samples or “cores” from the most productive areas or typical areas of a field. So that way the soil analysis guidelines are appropriate for the field average. Sample sites for this one composite must avoid hill tops, low spots and saline areas, for example. However, by avoiding these low-producing areas, agronomists and farmers may miss critical insight to boost yield potential in those areas. 

This is where a separate supplement soil test comes in. It may show something that could be solved, or at least improved, with targeted management.

A few potential target sample sites

  • An area always subject to lodging. Does it have high organic matter that kicks out a lodge-inducing nitrogen boost? It may be possible to reduce nitrogen rate in that area.
  • Hill tops. High ground often yields less because of low organic matter and less soil moisture. But perhaps low sulphur is also a factor in lower canola yields.
  • In-season problem areas. Zooming in on a specific problem area with soil and tissue samples could identify in-season issues that could be solved with a top dress. Take samples from the problem areas and compare them to samples from healthy-looking areas within the same field. (More on that in section three of this article.)

Cost and difficulty

COST: Around $100 per field to collect and analyze one targeted soil test.

DIFFICULTY: Easy

(Click to enlarge) Lyle Cowell, senior agronomist with Nutrien, provides this real example where he sampled the usual higher-yielding area and targeted a poor-yielding area in the same field. “A sample site in the poor area of a field may be of as much or more value than a composite sample from the good areas of a field,” Cowell says. “The composite sample missed that a potential huge part of the field was potassium deficient and that a targeted high rate of potassium in this area could greatly improve the yield potential.”

Nitrogen strips

Are you using the most profitable nitrogen rate? Growers and agronomists can learn a lot from a few strips of high nitrogen, and also low nitrogen.

Whatever nitrogen rate used, try a few test strips with 150, 125, 75 or 50 per cent of that rate. Compare yields with the combine yield monitor or, ideally, carts with scales. Results may support existing practices or identify a potential adjustment. If yields do not increase in the strips with higher rates, perhaps another nutrient is limiting or perhaps weather and soil conditions simply don’t support higher yields or higher rates of N. All of these are valuable learnings.

Cost and difficulty

COST: Urea in Western Canada as of March 2025 was around $900 per tonne, or 89¢ per pound of actual N. (That is up from $650 in July 2024 when we first ran these numbers for a Canola Digest article.) So a 100 lb./ac. rate of actual nitrogen (applied as urea) would be $89 per acre. An extra 50 lb./ac. (150 per cent rate) would add $45 per acre.

A 60-foot drill going the full length of a quarter section (2,640 feet) covers 3.6 acres, including the headland area. So $45 multiplied by 3.6 acres adds up to $162 per strip for the 50 per cent extra nitrogen. If you tried three strips per field and ran the experiment on three fields, the cost would be around $1,500. You could reduce the cost with 125 per cent instead of 150, and reduce it further by also trying some 50 per cent strips.

If the extra 50 lb./ac. of nitrogen increases yields by three bushels per acre in that strip, the experiment will about break even. If the increase is more, the experiment will make money.

DIFFICULTY: If applying nitrogen on its own (not in a blend), adjusting rates is relatively easy. Newer seeding systems control rates from the cab and, as one rep said, “it’s as simple as typing in a new rate as you are seeding.” You may want to confirm with your tool manufacturer whether fan speed also needs to increase for those high-rate strips. Growers and agronomists can also program trial strips into variable rate prescriptions.

Tissue tests

Canola Watch connected with a northern Saskatchewan agronomist who, in 2024, went to a canola field to check on “textbook sulphur deficiency.” The applied sulphur rate seemed reasonable, but with a wet May and June, sulphur likely leached down. Saturated soils early in the season also meant relatively shallow crop rooting depth. Just to be sure, the agronomist ran a tissue test – submitting leaves from sick-looking plants and leaves from nearby healthy-looking plants. Results came back in less than a week.

The recommended practice with a tissue test is to also submit separate soil samples from the area around the sick and health plants. This can indicate whether the tissue test results are due to an uptake issue (too much water for proper root function) or an actual soil shortage.

Tissue results in this case showed adequate nutrients, including sulphur, in the healthy leaves and acute sulphur deficiency in the sick leaves. The agronomist’s suspicions were confirmed. A localized sulphur top dress could help. In this case, given the late stage of the season, the farmer did not do a top dress.

Here are results from the A&L Laboratories tissue tests, shown in graphic form. Full results will show numbers as well. The top graph shows results from the healthy-looking plants. Unhealthy plants (bottom result) were short a number of key nutrients, suggesting a possible uptake issue. We don’t have soil test results to cross reference with actual available nutrient supply. 

Cost and difficulty

COST: A complete plant tissue test analysis (macros and micros) will be around $60. Two tests – one from a healthy plant and one from a poor plant – is $120. Tests for macros only will be cheaper. Analysis for a pair of soils tests is about the same price, and most labs do both soil and tissue analysis. Total cost: $240. This does not include the cost of collecting the samples. If the required treatment is a nutrient top-dress, this adds cost but these costs should be (hopefully) paid for with higher yields.

DIFFICULTY: As long as you follow the lab protocols, which are straightforward but specific, the tests are simple and practical.

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