Have canola growers been targeting too-dense stands?
According to one oilseed specialist that might be the case, but not everyone agrees.
Murray Hartman, oilseeds specialist with Alberta Agriculture and Forestry put forward the controversial suggestion during a presentation at Canolapalooza June 22 in Portage la Prairie. He says the current target of seven to 10 plants a square foot don’t produce enough added yield to justify the additional cost. A more profitable plant stand might be closer to four to six plants per square foot, he says.
“The actual, physical response of yield to density now is different with the herbicide-tolerant hybrids. We can achieve high yield with fewer plants than we used to,” he said, adding that the relative price of canola has changed with increasing seed costs.
Hartman did some rough calculations at the event, noting that lower seeding rates could bring producers as much as an additional $10 an acre or more, assuming canola prices of $10 and additional seed costs of $10 an acre. He also showed that higher-density seeding rates only broke back into profitability at lower emergence rates of 80 per cent or less, but profits were still higher in the lower-density model.
But while Hartman suggests that lower plant density might bring in bigger profits, his ideas raised questions from other experts.
Jeanette Gaultier, weed specialist with Manitoba Agriculture, said such economic-focused studies are too narrow and do not take proper agronomic management into account.
“Studies looking at the most ‘economic’ soybean and canola plant stands have found that producers may be able to seed less than recommended plant stands… but these studies only consider economics,” she said. “However, there are many less tangible seeding rate effects that producers should consider and weed control is a big one. Studies in various crops across the Prairies have demonstrated that increasing seeding rates increases crop competitiveness with weeds, which in all cases reduces weed biomass and weed seed return and, in many cases, increases crop yield. Decreased seeding rates, on the other hand, mean that our herbicides have to do all the heavy lifting due to a less competitive crop, which can increase the risk of selecting for herbicide resistance.”
Hartman acknowledged Gaultier’s point in Portage la Prairie June 22.
Along with weed concerns, the Canolapalooza instructor said a higher density would also provide more cushion in case plants are lost to disease, pests or weather through the season. Anticipated growing season may also affect optimal density, he said, since density can affect maturity.
“Most growers will say, well, I want extra seed because, for example, I might get flea beetles or some frost and things like that, and that’s fine,” he said. “My question is, do you know how much extra you’re willing to spend and what the extra value is to you?”
Hartman also said he is not advocating for every farmer to rein back on seeding rate. Many producers, he argued, may be overestimating their plant density and may already sit at densities at or lower than what his study recommends.
“If they’re counting their plant stands and they’re already at that low end, they shouldn’t be lowering it any more, but a lot of growers don’t measure what they have and they don’t realize they’re only achieving four plants per square foot,” he said.
“If you really want to be fine tuning your seeding rates with this expensive seed, you better be documenting what you have and figuring out whether you have room to go up or down,” he added.
The Canola Council of Canada (CCC) has joined further in the conversation around optimal seeding rate and plant density after launching its online canola calculator this year.
The tool includes several risk factors, including growing season length, frost, pest loss and non-uniformity, which producers may customize to mimic their farm’s environment.
Producers may calculate for seeding rate, plant survival or stand density using the tool.
“The CCC has been recommending plant density of seven to 10 plants per square foot, but emerging research which can account for equipment change, seed costs, seed size and improved vigour of hybrids indicates that growers may find situations where lower plant densities can still meet their goals,” CCC agronomy specialist Ian Epp said during the tool’s February launch.
Despite that, the council still recommends at least six plants per square foot due to potential plant loss.