Fine-tune your seeding rate to maximize yield

Just about every facet of canola production is characterized by science, precision and attention to detail. The canola seed you plant is likely a hybrid, carefully developed through modern breeding techniques, which include years of lab and field testing for yield and many other traits.

Every seed is treated to control earlyseason diseases and pests, and in some cases also coated with a biological or nutrient product to promote growth. Farmers pay close attention to soil tests, cropping history, and/or agronomist recommendations to develop a fertility program to meet yield targets.

Most producers regularly scout for pests; some even rely on drones to get accurate damage assessments. They carefully and accurately apply pesticides to control weeds, insects, and disease. Growers patiently open pods to determine the best time to harvest, and spend time fine-tuning combines to minimize harvest loses.

And yet, when it comes to seeding rates — arguably one of the most important steps for a successful canola crop — “acres per bag” is still how most farmers determine their seeding rate.

More farmers need to ensure they are calibrating their drill, as seed size can vary by a 100 per cent or more between varieties. Did you know, for example, that a 22.7 kg bag of large-seeded canola (7.5 g/thousand seeds) contains approximately 3 million seeds, yet a 22.7 kg bag of small-seeded canola (3.0 g/ thousand seeds) contains approximately 7.5 million seeds? That’s 2.5 times as many potential plants based on seed size alone!

SO WHAT IS THE BEST SEEDING RATE?

Rob MacDonald, product excellence at Bayer has a mantra: “Plant population matters!” He urges growers to seed at a rate that maximizes the genetic potential of the variety.

MacDonald points out that Bayer has identified the best seeding rate through what he calls “data driven agronomy.” For the past three years Bayer has conducted yield trials of varying seeding rates at 42 locations across the prairies.

Diverse locations mean these trials were conducted under a wide range of growing conditions from dry to wet, warm to cold, and with varying amounts of trash on the soil surface. Planting was done using highly accurate, scaled-down commercial equipment — exactly what farmers use, only smaller. Trials were both conventionally and zero-till seeded.

The trial results revealed a classic bell curve where yield increased with plant populations to a certain point, then began to decrease as populations increased. When all trial results were combined, the optimum plant population count was determined at 5-7 plants/ft2.

There are 43,560 ft2 in an acre, so theoretically a seeding rate of 217,800 to 304,920 seeds per acre should result in the ideal plant population to maximize yield potential. But as all farmers know, there can be wide discrepancies between theory and practice.

No matter how accurate your equipment and consistent your fields, not every seed will end up in moisture or at the depth needed for germination and survival. Seedlings can be stressed and die as a result of heavy trash, environmental conditions, disease or insects.

MacDonald suggests an initial seeding rate of 10 seeds/ft2, or approximately 435,600 seeds per acre for farmers aiming for a stand of 5-7 plants/ft2. Use the thousand seed weight (TSW) of your specific variety to convert into pounds per acre, or even acres per bag.

For example: If the seed has a TSW of 5 grams, to seed 425,000 seeds per acre would require 425,000 seeds x (5/1,000) = 2,125 g/ac. Converted to lb./ ac. that’s 4.68 lb./ac. (1 gm = .0022 lb.)

Not surprisingly, this is close to the traditional recommendation of 5 lb./ac. But if a variety’s TSW is only four grams, the optimum seeding rate would be 3.75 lb./ ac. Conversely, if the TSW is six grams, ac. to achieve a similar plant stand.

The big question is: “Will you actually achieve the optimum plant stand if you follow these steps and seeding at the correct rate for the variety?” MacDonald challenges the correlation between emergence and survivability. “It’s important to not overestimate your plant stand based simply on emergence.”

FALL STAND COUNTS

The most important step in determining the right canola seeding rate happens not in the spring but in the fall, says MacDonald. “Look at the plant population in the fall, after harvest of that year’s canola crop. It is so easy to do a plant count then.”

This comparison between your initial seeding rate and the actual plant stand represents survivability. It reflects the difference between the number of seeds planted per acre and the number of plants that actually grow to maturity and are harvested. It reflects the combined total of all losses arising from your seeding operation — equipment, timing, speed, pests, environment and management.

So the plant survival you achieve can be vastly different from your neighbour, who may be seeding a mile and a half faster or slower, or an inch deeper or shallower. It is why some farmers who have very accurate equipment and are careful to seed shallow into an ideal seed bed at a relatively slow speed are able to reduce seeding rates and still achieve a great plant stand. It is applying science to your individual canola seeding practice.

When conducting a stubble count in the fall, growers should also pay attention to the uniformity of the stand. The suggested plant stand target assumes a relatively even spacing of plants within the row, right across the field. The less uniform the stand, the more you have to increase the seeding rate to ensure you have an adequate plant distribution across the field.

MacDonald points out that by doing an accurate stubble count every fall and comparing that to your seeding rate from the spring, you can develop the baseline seeding rate you need to consistently achieve an optimum plant stand. With this knowledge, a grower can fine tune the suggested initial seeding rate of 10 seeds/ft2 up or down so that you will achieve the desired plant stand.

Corn and soybean growers are highly aware of the impact their seeding rate has on crops and have adopted seeding by unit rather than pound. Rather than do mathematical calculations to get an optimum seeding rate, they simply plant by seeds per acre. Given equipment improvements in seeding accuracy for small seeded crops, and the increased performance and consistency of seed, canola seeding by unit may be the next step for canola growers too.

IT’S NOT JUST YIELD

Canola is a very elastic plant, which to some degree, compensates for low or high seeding rates. While yield may not be impacted by plant stands as much as cereals are, the impact of a less than desirable plant stand is more detrimental in canola when other factors are considered.

MacDonald points out that seeding rate impacts much more than just yield. “A plant stand that is too low results in weed control challenges and delayed maturity,” he says. Given the amount of canola that was left over winter this year, it would be interesting to know how much of this was seeded with a low seeding rate and simply did not mature and dry down before winter set in.

Too low seeding rates can lead to large bushy plants that present harvest challenges such as swath timing, insufficient stubble to hold the swathes, and increased potential for shelling due to delayed maturity and uneven ripening.

Too high seeding rates can lead to very dense stands with a lot of in-row competition for nutrients, more rapid spread of disease and increased risk of lodging due to thin stems. Plants can be up to 10 cm shorter, which can present a whole different set of harvest problems.

There’s no question you can grow a good canola crop with a wide range of seeding rates. But you should be striving for the seeding rate that maximizes the genetic potential of the plant. Simply using the “acres per bag” approach may not get you there today. FF