In one case this year, a grower seeded 2.2-gram thousand seed weight (TSW) canola seed at 5 lb./ac. With very good seed survival due to warm, moist soils, the crop now has 20 plants per square foot. Is the intense competition between these crowded plants likely to result in lower yields?
The Canola Encyclopedia says: As the canopy becomes more dense (plant population increases), each plant produces less dry weight, thinner stems, fewer branches and fewer seeds per plant due to increased competition from adjacent plants. However, fewer seeds per plant are offset by a higher number of plants, resulting in similar seed yield per unit area compared with lower plant populations. This is why canola can produce similar yields over plant populations ranging from 50 to 200 plants per metre square (5 to 20 per square foot). In a canopy with more than 200 plants per square metre (or 20 per square foot), stems are very thin and pods are concentrated at the top of the plants. These stands are more likely to lodge, which can create a better microenvironment for diseases like sclerotinia and make harvest more challenging. Severe lodging during bolting or early flowering stages may also directly impede the efficient uptake of moisture and nutrients through stem crimping, leading to lower yields. Read the original Canola Encyclopedia section.
Benefits of more plants. Higher plant stands can provide agronomic benefits for integrated pest management. These benefits include increased weed competition and potentially higher early-season insect thresholds.
Economics. At the end of the day, this grower could have taken advantage of the smaller seed size and seeded fewer pounds per acre. As described in the Encyclopedia, a plant stand half of what he achieved would likely yield the same, could still achieve similar agronomic benefits and cost a lot less in seed, thereby improving profitability. Using the Seeding Rate Calculator at canolacalculator.ca, the grower would have found that a lower seeding rate would be acceptable to achieve the target stand. The seed savings could have been transferred to another field that might have had larger seed and needed a higher seeding rate.