As air drill technology continues to improve, new designs are enabling farmers to get more accurate, even placement in the seed row than ever before. But should farmers use the advantages offered by these modern systems to cut back on seeding rates, particularly in canola? Purchasing canola seed can represent a relatively large input cost, especially when compared to cereals. Reducing seeding rates could provide a significant cost saving, making scrimping on seed a tempting idea.
“If [a drill] can put seed evenly along the row, that’s great. That’s what we’re looking for,” says Doug Moisey, senior agronomist at the Canola Council of Canada. “The bottom line is (with even spacing) you decrease plant competition along the row.”
Randy Kutcher, a research scientist with Agriculture and Agri- Food Canada, agrees. “If you’re going to a wider row spacing, it’s more of an issue not to have seeds clumped together,” he says. “It’s better to have a uniform spacing.”
But farmers still need to shoot for ideal plant populations in order to maximize yields. “I really don’t care what your seeding rate is as long as you end up with five to ten plants per square foot at harvest,” says Moisey. That doesn’t just mean seeding at higher rates; in most cases, it means doing everything right, including putting enough seed down.
Farmers aiming for the lowest effective plant population, though, would have to work precisely and very carefully during seeding. “You’re walking a tightrope,” he says. “I believe we lose more yield in the first 20 days of the season because of the little things we do.” Things like excessive seeding depth can reduce germination and hamstring a field’s yield potential.
“The risk is at the seedling stage,” Kutcher echoes. “The difference between three and four pounds per acre can make the difference between having to reseed a crop or not (if early growing conditions are poor). It’s especially the flea beetles and seedling diseases that pose the risk.”
SEED BY 1,000 KERNEL WEIGHT
If a grower is willing to accept the challenge of getting seeding rates down as low as possible, they will need to know the precise weight of the seed being used before setting meters on a drill. The seed size of different canola varieties can vary greatly, some samples can weigh as little as four grams per 1,000 kernels and other types can exceed six. “If you’re using a newer variety at 6.1 or 6.2, you may not have enough plants (at low seeding rates),” says Moisey.
But in some circumstances there may be merit in keeping seeding rates low. Research conducted by the Canola Council of Canada on plant populations showed aiming for plant stands at the low end of the acceptable
range did show some benefits in drier years. Under dry conditions, plots with lower plant counts typically yielded better than the higher-density stands. Placement accuracy played a role in getting those results. Moisey points out the stands were uniform and evenly distributed across the plots.
And lower-density stands can produce more seed per plant than those seeded at higher rates. Because
plants don’t have to compete with each other for moisture and nutrients, each one tends to produce more pods and, therefore, more seeds. That makes each plant in a low-density stand more productive.
“With relatively low populations, plants will branch out more to compensate,” adds Kutcher.
But there is a limit to the benefit. Moisey points out that even though plant stands below critical levels in the research trials produced more pods per plant, overall there were fewer pods per square metre, which still translates into reduced yield.
HARVESTABILITY AND PEST PRESSURE
There are other downsides to low-population stands. “Canola is basically an indeterminate crop. If you keep feeding it, it will keep growing. It needs stress to stop growing come harvest time,” says Moisey. That means maturity in a low-density field will be delayed, creating problems if early season frost becomes a threat. “When secondary and tertiary pods start forming, that delays maturity,” he adds.
“In research we conducted going to two plants per square foot versus five, maturity was delayed by as much as 18 days in some locations,” he says. This is an extreme example of the effects of lower plant populations, but a valid one.
In addition, low plant numbers can leave little cushion if diseases become a problem. “We had issues this year where a lot of guys had ten plants per square foot and they were happy they did, because they lost a couple of plants per square foot due to seedling diseases,” explains Moisey.
Dealing effectively with in-season pests and disease in low density stands will require increased monitoring. “Threshold levels for pests might have to be reevaluated,” he says. Farmers whose fields have low plant numbers may find they have to apply pesticides in cases where they otherwise might not, adding to production costs. Losing two plants per square foot in a stand of five is much more significant than losing the same number in stands of ten.
PLANT DENSITY TARGETS
Farmrs toying with the idea of reducing seeding rates need to know what plant populations their fields averaged over the past couple of years, Moisey believes.
“If you are targeting five plants per square foot, basing seeding rates on 60 per cent emergence and we get a real cold spell that delays emergence, rates could drop to 40 per cent, which puts you at three plants,” he says. “At those levels there is no margin for error. As well, the question is will it emerge evenly? Research has shown that nonuniform stands can cost 20 per cent in yield losses.”
With so many possible pitfalls to cutting seeding rates to the bone, Moisey advises against it. Instead, he advocates targeting a uniform stand of 10 plants per square foot to start the season on the right foot.
“If you’re going to play it close to the edge, you have to be on top of everything,” he says.
Contacthimat [email protected]
The difference between three and
four pounds per acre can make the difference between having to reseed a crop or not.