Plant count vital when evaluating seeding practices

Canola growers need to walk into their crops and count the number of plants per square foot, says a Canola Council of Canada agronomist.

Doug Moisey, who works in central Alberta, told a recent webinar that fields with insufficient or inconsistent plant densities will generate significantly lower yields.

“It’s really critical that we get producers to try and get to that five plants (per sq. foot) or better during the growing season,” he said.

According to a survey done by Agriculture Canada researcher Julia Lesson of Saskatoon, many canola growers in Western Canada aren’t achieving five plants per sq. foot. Leeson surveyed 218 canola fields in Alberta last year and found that 34 percent had less than four plants per sq. foot.

However, Moisey said most growers don’t know how many plants they have per sq. foot. A canola council survey found that “approximately 75 percent of producers do not do plant counts.”

Yantai Gan, an Agriculture Canada scientist in Swift Current, Sask., said a plant count is needed to evaluate seeding practices.

For instance, if a grower seeded at nine pounds per acre but only grew 3.7 canola plants per sq. foot, it would mean that seed survivability was low, possibly because the seeds were planted too deep or the seeding speed was excessive.

Growers who don’t have plant counts from previous years won’t know how to adjust seeding practices in the future, he added.

“Some farmers, they look in their field and they say, ‘yeah, my canola looks OK,’ ” Gan said. “But they don’t know how good it is.”

As part of the flax-canola Canadian science cluster, Gan and his colleagues have conducted field trials at multiple locations on the Prairies to assess the impact of uniform plant stands on seed yield and quality.

Based on results from sites near Brandon, Gan found plots with 2.8 plants per sq. foot yielded 25 bu. per acre, while fields with 7.4 plants per sq. foot yielded 37 bu. per acre.

Gan said factors that determine how many canola plants will grow in a sq. foot include:

  • seeding rate
  • seed vigour
  • uneven seeding depth

Gan advises canola growers to use higher seeding rates, such as eight to nine lb. per acre, but producers often tell him they use six to seven lb. per acre.

Moisey said some producers still follow the rule of thumb of five lb. per acre, but that rule is no longer valid.

“The five lb. per acre adage doesn’t (hold true) anymore. With bigger seed size, you’re not going to be getting the plant populations you hope.”

Gan said canola growers should set a target of 5.6 to 7.4 plants per sq. foot.

Last year he and other Agriculture Canada scientists in his project visited about 60 canola fields to count plants and determined that most prairie fields have less than 5.6 plants per sq. foot.

“Most out there are between 30 to 60 plants (per sq. metre, or 2.8 to 5.6 plants per sq. foot). A very few farmers were over 60 plants (per sq. m, or 5.6 plants per sq. foot).”

Gan seeded plots to achieve a specific number of plants per sq. foot, ranging from 1.9 to 9.3 plants. The scientists then removed a number of plants in each trial with 1.9, 3.7, 5.6, 7.4 or 9.3 plants per sq. foot. That way, they had a control plot with a uniform plant stand and another plot with a non-uniform stand.

After evaluating results from 2010 and 2011, Gan determined that uniform stands preserve yields when plant populations are low.

“(At) 20 to 40 plants per sq. m (1.9 to 3.7 plants per sq. foot), the uniform plant establishment will increase yield by 11 to 19 percent over the non-uniform plant establishment,” he said.

There was minimal difference in yield between uniform and non-uniform stands when plant counts were higher than 5.6 per sq. foot.

Gan said fields with varying plant concentrations, or patches of high and low concentrations, generate lower yields for two reasons:

  • when the population is low, weeds grow in the open spaces between plants and remove nutrients from the soil
  • plants in low density produced branches later in the growing season. Pods often formed on those branches but they didn’t contain seeds

“So the plants are wasting their energy by producing those late em-erging branches and late emerging pods.”

Gan will do one more year of field work on canola plant stand uniformity this summer to collect more data on seed yield and quality.

The final results of the study will likely be published in 2013.

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