Canola seeding rate: hitting 50–80 plants per square metre

The formula

Three inputs, no constants in metric:

Seeding rate (kg/ha) = target plant density (plants/m²) × TSW (g per 1,000 seeds) ÷ expected emergence (%, as a whole number)

Dividing by the percentage as a whole number (60, not 0.6) is what makes the metric version clean: the conversions from grams to kilograms, square metres to hectares and per cent to a fraction cancel to exactly one. The Canola Council's imperial form, used by its online calculator, is:

Seeding rate (lb/ac) = 9.6 × target plant density (plants/ft²) × TSW (g) ÷ estimated seed survival (%, as a whole number)

The two give the same answer. Converting between them: 1 kg/ha = 0.89 lb/ac, and 10 plants/m² is roughly 1 plant/ft² (the exact factor is 10.76). Watch the unit on the target: Prairie targets are usually quoted per square foot (5 to 8), which is 50 to 80 per square metre, and mixing the two is the most common error in this arithmetic.

To work backwards after emergence, seeds sown per square metre is kg/ha × 100 ÷ TSW (g), and emergence is the plant count divided by that.

Inputs and where to get them

Target plant density. Start at 50–80 plants/m² (5–8 plants/ft²). The Canola Council's target density calculator moves the number within that range: lower when expected weed competition is low, higher when spring frost risk is high, because the target is an established stand after season-long losses, not the stand on emergence day. Stands of 30–40 plants/m² can still reach yield potential if uniform, but a Swift Current study cited by the Council found thin, patchy stands yielded well below dense, even ones when moisture was short.

Thousand seed weight. Read it off the seed tag; it changes with every lot. Current hybrids run from about 3.5 g to 6.5 g or more per thousand seeds. At the same kg/ha, a 4 g lot puts down 50 per cent more seeds than a 6 g lot, which is why calibrating the drill between seed lots is not optional.

Expected emergence (seed survival). The Canola Council reports that 50 to 70 per cent is typical and uses 60 per cent as the calculator default; 50 per cent is common, and field results range from roughly 25 to 75 per cent. The only good source is your own plant counts from previous years on the same drill, soil and fertilizer practice. Without those, assume 50 to 60 per cent and start counting.

Worked example

Field: 64 ha (158 ac), target 70 plants/m² (about 6.5 plants/ft²) to leave a buffer for flea beetles and frost. Seed tag: TSW 5.0 g. Last two years' counts on this drill averaged 60 per cent emergence.

1. Seeds needed: 70 ÷ 0.60 = 117 seeds/m².
2. Weight of those seeds: 117 × 5.0 g ÷ 1,000 = 0.58 g/m².
3. Scale to the hectare: 0.58 g/m² × 10,000 m² = 5.8 kg/ha.

Or in one line: 70 × 5.0 ÷ 60 = 5.8 kg/ha (5.2 lb/ac). Imperial check: 9.6 × 6.5 × 5.0 ÷ 60 = 5.2 lb/ac. For 64 ha that is about 373 kg (822 lb) of seed.

The same target with different inputs:

Across a row, the cost of a poor seedbed is visible: dropping from 60 to 50 per cent emergence needs 20 per cent more seed for the same stand. Down a column, a heavy seed lot at a fixed 5 lb/ac delivers far fewer plants than a light one.

The reverse calculation. Three weeks after seeding, a 0.25 m² hoop count on that field averages 14 plants, or 56 plants/m². Seeds sown were 5.8 × 100 ÷ 5.0 = 116 per m², so emergence was 56 ÷ 116 = 48 per cent. The stand is adequate, but next year's calculation should use 50 per cent, not 60, unless the seedbed changes.

Counting plants after emergence: the hoop method

Start checking 10 days after seeding in good conditions, 15 days if it has been cool, and do the formal count at the two- to four-leaf stage, alongside scouting for the first herbicide pass. The Canola Council describes two hoops:

• Metric hoop, 0.25 m²: inside diameter 56 cm (circumference 177 cm). Toss it, count the canola plants inside, multiply by four for plants/m². Divide that by 10 for plants/ft². Example: 16 plants × 4 = 64 plants/m² (about 6.4 plants/ft²).
• Imperial hoop, 2 ft²: inside diameter 49 cm (circumference 153 cm), wide enough to span two seed rows. Divide the count by two for plants/ft², multiply by 10 for plants/m².

Or use a metre stick along one seed row: plants per metre × 100 ÷ row spacing in cm = plants/m²; 25 plants in a metre of row at 25 cm (10 in) spacing is 100 plants/m².

Count only plants with the blue seed coat still attached to the root, so volunteers are excluded, and skip plants outside the seed rows. Take several counts per field and average them; if emergence is patchy, dig along the row for ungerminated seed. Mark a count site and recount after harvest: the difference between spring and fall is your season-long plant loss, and it belongs in next year's target.

Caveats and adjustments

Emergence is the input you control at seeding. The Canola Council lists soil moisture, soil temperature, seed depth, seeding speed, seed placement and seed-to-soil contact, fertilizer toxicity, seed vigour, seedling disease and insects as the factors that drive it. The ones worth money:

• Depth. Target 1.25–2.5 cm (0.5–1 in). In a study the Council cites, average emergence rose from 37 per cent at 4 cm to 62 per cent at 1 cm under moist conditions. Deep seed runs out of stored energy before the cotyledons reach light.
• Speed. Faster travel throws soil, bounces openers and widens the spread of depths across the drill. Check depth at the speed you actually seed.
• Fertilizer in the seed row. Canola is sensitive to seed-placed nitrogen, potassium and ammonium sulphate. Phosphate is the only nutrient the Council considers safe with the seed, and only to about 20 lb/ac of P₂O₅ (roughly 22 kg/ha) at typical openers; band the rest. Turning off seed-row fertilizer on a few 30 m (100 ft) strips and counting plants in both is the cheapest trial you will run.
• Seedbed and soil temperature. Cold, cloddy or dry seedbeds stretch emergence and expose seedlings to flea beetles and frost for longer. If the top 2.5 cm is dry, the Council allows seeding to 4 cm when soil is warm and no rain is forecast, expecting emergence to drop.
• Seed size at a fixed rate. A heavy lot at the same kg/ha quietly cuts your plant count. Recalculate for every lot.

The formula only turns a target into a drill setting; it does not choose the target. Thin, uniform stands can yield, but they lose the buffer for frost, flea beetles and cutworms, mature unevenly and shade fewer weeds. Seeding above 80 plants/m² adds seed cost and, the Council notes, can raise lodging and disease risk, with little yield in return.

Do it for your field

Pull the TSW off this year's seed tag, use last spring's hoop counts for emergence, and the rate in kg/ha and lb/ac falls out in one line.