New canola varieties and changing economics have pushed target plant stands lower, says Murray Hartman, oilseed specialist with Alberta Agriculture.
The “economic sweet spot” is now four to six plants per square foot, Hartman told farmers and agronomists at the Canola Council of Canada’s CanoLAB in Vermilion, Alberta.
Hartman recently reviewed published trial data looking at canola plant density. Based on that review, he determined that farmers can achieve optimum yield at a much lower plant density than with older varieties. Combine that with the higher cost of hybrid seed, and it only made sense to lower plant stand recommendations.
But that doesn’t necessarily mean farmers should cut back on seed. “I’m talking plant count. Not a seeding rate,” said Hartman.
Dan Orchard, agronomist with the Canola Council of Canada, stressed that “if you don’t know what your plant density is, on average, in your field, you don’t know if you need to seed heavier or lighter.”
Emergence is going to change every year, Orchard said. By documenting emergence each year, farmers can compare poor emergence to previous years, and figure out what’s going on, he explained.
Very few farmers physically count plants and track that information year to year. Hartman said farmers tend to get behind with so many fields to scout. Volunteers in short rotations also make it tricky to get an accurate plant stand count, he added. Counting volunteers in an area where a farmer had a seeding miss is one way to figure out actual plant stand. Hartman also recommended counting volunteers between rows.
Orchard says farmers should look into having their agronomists do plant stand counts. “And if not, then the farmer needs to keep records because I think it will pay huge dividends.”
Advantages of a thicker stand
Hartman said the revised four to six plant stand target is “kind of an economic minimum.” There are many reasons a farmer might want to bump the plant stand density on a particular field.
Farms with consistent frost problems might want a higher seeding rate. A thicker plant stand also defends against some insects such as flea beetles and root maggots. However, more plants won’t help with a cutworm problem, as the nasty little creatures will take out whole patches.
More canola plants also mean fewer weeds. Most canola growers have weeds under control in their fields, Hartman noted. But farmers concerned about herbicide resistance might favour a thicker plant stand.
Denser plant stands also have some advantages when it comes to harvest, Orchard said. For example, farmers who straight cut might want a thicker stand. More plants also anchor swaths better than lighter stands, which might be a concern in windy areas. And a thicker stand means more even crop maturity, which simplifies harvest timing. Orchard pointed out that swath timing recommendations are based on seed colour change on the main stem. However, thinner crops will have more yield on the branches.
There’s a data gap on fungicide applications to control sclerotinia in uneven crops with plenty of branching, Hartman said. But based on an educated guess, he thinks crops with lots of branching, and more yield on the branches could suffer late infections if conditions are right. Orchard pointed out that insect thresholds and herbicide application timing recommendations are also based on thicker plant stands.
But does a thin stand decrease sclerotinia?
“The problem with sclerotinia is that it doesn’t want to co-operate with trials. We can very rarely get good data. For the most part, the impact of seeding rate and row spacing has been minimal on sclerotinia,” said Hartman. He added that sclerotinia does spread more quickly when plant stands are so thick that there is stem-to-stem contact.
Farmers facing a shorter growing season might be concerned about days to maturity and green seed counts. Hartman reviewed a large scale Canola Council trial. When plant counts dropped to four to six (from seven to 10), there was a two-day increase in days to maturity. Plant stands of two faced a week or two-week increase in days to maturity.
As for green seed count, a stand of four to six plants did see more green seed. “But usually it’s not enough where you actually lose a grade,” said Hartman. Dropping below four plants will likely drop a grade as well, Hartman said.
It’s not unusual to see gaps in rows, especially in fields with heavy residue. Hartman said Agriculture and Agri-Food Canada researchers found that canola crops with gaps need more plants to fill in those holes and hit yield potential, compared to uniform stands. Farmers with heavy wheat crops would likely want to bump seeding rates, unless they change their residue systems, he added.
Other ways to boost plant count
Farmers will need to figure out how much more they need to spend on seed to get an effect that’s worth it, Hartman said. But buying more seed isn’t the only option.
Canola seed typically runs from 50 to 70 per cent emergence, Hartman said. “If you’re only at 50, can you jump to 70 by changing some of your management? Absolutely.”
Slowing down while seeding is one option, Orchard said. “But logistics trump agronomy.”
If excess residue is affecting emergence, removing straw is an option, Orchard said. A lot of the carbon is below the soil, so there isn’t much of a penalty for removing excess straw, he added.
Factoring in seed size and seeding depth can also boost emergence. On display in a tub were three rows of plants of different seed sizes. Half the tub was seeded at half an inch, and the other half at 2.25 inches. The large seed produced larger cotyledons, which covered the ground more quickly.
Orchard suggested taking a look at thousand kernel weight when picking up seed. Farmers might want to plant larger seed first, assuming that seed will be placed deeper. Other potential spots are weedy fields or poor seedbeds where a farmer might accidentally seed deeper.
Seed-placed fertilizer is another potential area for improvement. Some farmers who are placing a little too much fertilizer with the seeds still get good yields, Hartman said. But there’s a cost to killing seed in the ground, he said, and farmers could use that money elsewhere.
Orchard has seen 50 per cent of the seeds burned in one field. The farmer had accidentally shut off the seed-placed fertilizer for about 300 feet, and he had double the plants in that stretch, Orchard said.
Orchard advises farmers and agronomists to strike it off their list of potential problems before they start seeding. A seed-placed fertilizer problem is tough to diagnose after the fact.
“You can barely find the seed behind the drill, let alone three weeks later when everything’s gone,” he said.
The key to knowing whether you need to boost or can cut your seeding rate is counting seedlings. The Canola Council of Canada suggests hitting the field 10 days after seeding if conditions are good. If it’s been a cool spring, give the crop 15 days.
Farmers and agronomists can use a hoop with an inside diameter of 56 cm, the Council states. Alternately, a 50 cm x 50 cm square will work. Both those options work out to 0.25 metres squared. After counting the plants within the hoop or square, multiply by four to figure out the plants per square metre.
A person can also use a metre stick to count the seedlings in a metre of row. Multiply that number by 100. Divide by the seed spacing (in cm) to figure out seedlings per square metre.
To convert plants per square metre to (approximate) plants per square foot, divide by 10.