One in three for canola and pea

Stu Brandt, research scientist with Agriculture and Agri-Food Canada in Scott, Sask., shared his research on intensive canola and pea rotations at the Manitoba Agronomists Conference in December. You can see his presentation by going to www.umanitoba.ca/afs/agronomists_conf and clicking on “Webcast Archive.” You’ll find a video of his talk, called “Intensive canola and pea.”

The seven-year study was conducted at Scott and Melfort locations from 2000 to 2006. It compared these rotations: continuous canola, continuous pea, canola-wheat, pea-wheat, wheat-pea-canola and wheat-pea-wheatcanola. The study was conducted to see if the recommended one in four year rotation for both crops was still warranted. The one-in-four recommendation was set 15 years ago, or so, based on disease and weed pressures that would build up with tighter rotations.

Conclusions for canola:

Canola yields were the worst in a continuous rotation. Canola yields went up dramatically when you added a year of wheat in between, and yields were best in a wheat-pea-canola rotation where canola was planted once every three years. This rotation, especially when the canola was a hybrid, also had the best overall net returns based on a yearly average.

The study compared two varieties of canola — an InVigor hybrid and the old open-pollinated Westar, which the original recommendations were based on. Westar is susceptible to blackleg. InVigor, like most new canola varieties, has a “resistant” rating for blackleg. This makes a big difference. “Genetic resistance is the most effective tool for blackleg management,” Brandt says, which is why farmers can get away with tighter rotations these days.

Brandt also noted the type of canola you grow — high-yielding hybrid or lower-yielding OP — has no bearing on yield for the following wheat crop. Whether wheat followed a high-yielding canola crop or a low-yielding canola crop, it had, in general, no influence on wheat yield, he says.

Conclusions for peas:

Weed control is the major drawback for tighter pea rotations. In continuous peas, there were more cleavers in the field than peas by the seventh year. “By 2006, we associated a 60 per cent yield loss to cleavers alone,” Brandt says. You need at least a one-year break between pea crops to introduce a different mode of weed control.

As for disease, Brandt says the poorest response from fungicide application came in the continuous pea rotation. This was a surprise, he says. They expected fungicides to provide the greatest return when disease pressure was highest. He suspects that inoculum levels were so high in continuous peas (and canola) that fungicides couldn’t keep up. His recommendation for peas, based on the study, is to use a fungicide when yield potential is high. “It can provide a 20 to 25 per cent yield boost in these conditions,” he says. “The challenge for farmers is to determine a crop’s yield potential early enough to know that a fungicide application will pay off.”

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