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Wide range of seed weights

Before you set your seeding rates, look at these relationships 
between seeding rate, seed size and seedling survival

Editor’s note: In last week’s “Grainews,” an article on thousand kernel weight went through the math of using seed weights to calculate seeding rates. This article from the Canola Council shows the relationships between seed size, seed rates and seedling survival in canola.

Thousand kernel weight (TKW) for canola seed can vary from less than three grams to more than six grams. Last spring there were reports of wide ranges in seed size, even among seed lots of the same variety. Look at the TKW for each seed lot, and calibrate the drill to achieve your target plant population for each seed lot.

Seed each seed lot separately. Mark the field where you change lots. Keep a sample of each lot.

If you plan to seed at five pounds per acre regardless of seed size, know the risks. Large-size seed planted at five pounds per acre may not achieve the safe minimum plant stand of seven plants per square foot.

A six-gram hybrid seeded at five lb./ac. works out to 8.7 seeds per square foot. At 60 per cent seedling survival, which is at the high end for average conditions, those 8.7 seeds only produce 5.2 plants per square foot. At rates below five lb./ac., the plant stand drops accordingly. The combination of lower seeding rates and large seed size can lead to disappointing plant populations and a significant drop in yield potential.

With at least seven plants per square foot, you have some margin for losses to insects and disease.

higher seedling survival

Farmers can take extra precaution to increase seedling survival. Such as:

Seed into warm soils: This will increase seed survivability, especially if you have a heavy seed lot which will result in fewer seeds per pound going into the ground. Seed one-half to one inch deep. Shallow seeding is recommended for all canola because it increases seedling survival. Keep seed-placed fertilizer at a safe level.

Bulking agents: Most drill tanks sold in Western Canada are made to handle small seeds such as canola and deliver relatively uniform seed counts to each row. For a drill that cannot accurately meter small seeds and low flow rates, bulking agents such as elemental sulphur, seed-sized starter fertilizer prills, or cracked oat groats may help.

However, the Canola Council of Canada ran trials in 2001 and 2002 to evaluate pelletized elemental sulphur at 22.5 kg/ha (20 lb./ac.) as a seed-bulking agent. This research found no consistent stand establishment or yield benefit when using the bulking agent, since the treatments without bulking agent generally produced more than adequate plant populations. Bulking agents are likely not necessary unless your drill is quite ineffective at delivering low rates of small seed. If using a bulking agent, ensure seed and bulking agent stay uniformly mixed throughout the seeding operation.

Three-way relationship

The charts to the left show the three-way relationship between seeding rate, seed size and estimated seed survival.

For example, if you hope to get 60 per cent seed survival, go to the chart with 60 per cent at the top. If your seed size is five grams per 1,000 kernels and you want to seed at five lb./ac., you can expect 6.3 plants per square foot. The ideal plant stand for yield potential and uniform growth, with some cushion for plant loss to insects and disease, is seven to 14 plants per square foot.

The minimum before you face a higher risk of yield loss is five plants per square foot. All cells in white in the charts are this high risk zone.

This article originally ran in the April 25, 2012 issue of “Canola Watch.” Find “Canola Watch” online at www.canolawatch.org. †

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