Seven to 10 plants per square foot emerged uniformly. That’s the target. That’s the ultimate goal with canola stand establishment.
“A simple straightforward approach is to stick with the common seeding rate of 5 lb./ac. That rate often produces enough plants per square foot to maintain yield potential and is easy to remember,” says Justine Cornelsen, agronomy specialist with the Canola Council of Canada. “Trimming rates below that standard tends to miss the target plant stand — and thin stands mean lower profits.”
Various profit-reducing factors result from a thin stand. First, stands of fewer than five plants per square foot have lower yield potential. Hybrid canola studies show that stands of three plants per square foot yield around 80 percent of stands with five or more plants per square foot. “Shaving the seeding rate from 5 lb./ac. to 3 lb./ac. may save $20 per acre, but if yield drops by 20 percent — say to 32 bu./ac. from 40 — that chops revenue per acre by $80,” Cornelsen says. Targeting seven to 10 per square foot allows for some plant loss during the season so harvest counts remain at or above this critical five-per-square-foot threshold.
Second, thin stands tend to mature later. Each plant in a thin stand will have more branches, which means seed maturity on later branches will be well behind the main stem.
“Harvest timing for this crop is much more difficult, and growers will have to decide between letting the side branches mature long enough to produce viable seed or cutting on the early side to limit shelling losses on the main stem,” Cornelsen says. “And because a thinner stand takes longer to mature, this also increases the risk for frost and green seed.”
It only takes two percent green seed to drop to a No. 2 grade, which usually has a discount of at least $10 per tonne. At 40 bu./ac., that’s $10 — often more — per acre.
Thin stands tend to require more inputs to keep those few plants alive and competitive. The flea beetle threshold, for example, is based on leaf area loss but with a consideration for plant counts. With seven to 10 plants per square foot, growers can afford to lose one or two to flea beetle damage and still be at or above five per square foot.
“With a thin stand, canola is more likely to need protection from flea beetles, cutworms or whatever else comes along,” Cornelsen says. “The cushion that a healthy stand provides just isn’t there.” Typical cost for an early-season insecticide spray is $5 per acre plus application cost.
With fewer plants, the canopy takes longer to fill and can’t compete strongly with later weed flushes. This may increase the need for a second in-crop herbicide application. Product, application and time required for that second in-crop application will be $8 to $20 per acre.
Thin stands can also make the sclerotinia stem rot spray decision more difficult. Large leafy plants with many branches are still at risk from sclerotinia stem rot. More branches mean a longer flowering period, which may increase the need for a split fungicide application to keep the crop protected. Complete cost of a fungicide application is $25 to $30 per acre. Double that for a split application.
A more refined seeding rate
Growers who want a precise seeding rate that hits the seven- to 10-plant target will tweak the five-pound rate based on thousand seed weight (TSW) and on seeding conditions. Seed lots with a higher TSW have fewer seeds per pound, and therefore more pounds per acre are needed to achieve the target stand.
As for seeding conditions, emergence rates tend to be much higher in warm and moist soils. “Growers may want to seed at a higher rate in cold soils, high-residue fields or other situations that reduce seed survival, then seed at a lower rate on fields with excellent emergence expectations,” Cornelsen says. “At the end of the seeding season, growers will have used the same amount of seed but applied it in such a way that improves overall stand establishment and provides a better return on the seed investment.”
Other factors that can increase seed survival are:
Seed shallow. Half an inch to 1” below the packer furrow is the recommended seed depth for canola.
Seed at a consistent depth. Too shallow or too deep will both reduce emergence rates. Achieving consistent placement often depends on a level drill and well-maintained openers.
Seed at the right speed for accurate placement. The ideal speed will vary by drill and soil conditions. In general, at higher speeds, rear openers tend to throw more soil over the front rows. Seed in these front rows will be buried deeper, making them slower to emerge.
Limit seed-placed fertilizer. The best practice is to place only phosphate fertilizer with the seed following safe rate guidelines (20-30 pounds of phosphate per acre depending on soil conditions) and put other nutrients away from the seed row.
Penetrate residue. Spread residue evenly in the fall, and have a drill that can penetrate this layer so all openers place seed into the soil.
Leave a firm seedbed. Openers that fracture the seedbed, worn openers that do not provide a defined seed ledge and high fan speeds that cause seed bounce can reduce an opener’s ability to place seed precisely.
Pack appropriately. In wet conditions, reduce packing pressure to limit hard crusting. In dry conditions, pack more to conserve moisture in the seed row.
Source: Canola Council Canada