Harvest plant counts can help growers determine if their seeding was adequate to reach the crop’s yield potential. A compilation of stand establishment research shows that canola generally needs at least 4-5 plants per square foot to reach its yield potential.
But is this true for all varieties, all crop inputs packages, and all growing conditions? We don’t know. Growers can start to figure out their own ideal target plant stand by collecting a few years’ worth of plant stand data cross referenced with yield. Compare plant counts and yield for each field. Some growers may find that 4 plants per square foot does provide their highest yields, with similar management. Others may find that 10 or 15 plants is better.
With this information, growers can start to run their own economics on seeding rates. They will be able to determine, for example, that a seeding rate higher than 5 lb./ac. does actually provide a strong return on investment if it means they’ll hit a target plant stand that works best on their farm.
It may take several years to compile enough data to be useful. Also when setting seeding rates for next year, note that seed survival was much higher than average this year, in general. This is why a few years’ of data is important.
When comparing harvest plant stand counts to post-emergence counts, there is often a 10-15% drop in plant numbers through the season. (If there is an increase, which is also possible, take a close look at all plants in the harvest count to see how many are actually contributing to yield. Small spindly plants that emerged well after all the other may not have that many pods, and should not be included in the count.)
How to count: To do a stem count, growers can (1) count the stems per metre of row. Take that number and multiply by 100 then divide by the seed row spacing in cm to get plants per square metre. For example, 25 plants per metre multiplied by 100 then divided by 25 cm (10” row spacing) is 100 plants per square metre. Divide by 10 to get plants per square foot. Another way is to (2) use a hoop with an inside diameter of 56 cm. This is equivalent to 0.25 of a square metre. Count the stems inside the hoop, and multiply by 4 to get plants per square metre. Then divide by 10 if you want plants per square foot. Repeat counts a few times throughout the field.