Looking for a sure fire, low-cost way to boost canola yields by 10 to 20% this year? Simple. Avoid planting canola on last year's canola stubble, says Derwyn Hammond, Agronomist, Manitoba for the Canola Council of Canada. Stick with a one-in-four rotation for long-term success, he adds.

"Research trials and crop insurance data show canola yields are higher following cereals, flax or a pulse crop than following canola, often by as much as 10 to 20% or more. Each of these crops in turn also fairs better when seeded into canola stubble, with the exception of flax which can suffer from phosphorous (P) deficiency due to reduced levels of vesicular-arbuscular mycorrhizae--the fungi which aid in making soil P available to plants," he says.

Under continuous canola cropping, pest populations increase, especially if the pest has limited mobility. Diseases that survive in the soil (such as seedling diseases, root rots, and clubroot) or on crop residue (such as
blackleg) fall into this category, as would most weeds.

"It can be tempting to stray from the recommended one-in-four canola rotation, particularly when canola prices are high. However, over the long term, following the recommended canola rotation can provide better yields with reduced risk for all crops in the rotation.

"Keep in mind that there is a new strain of blackleg in some parts of the prairies. Old diseases are changing and new diseases are being found. It's even more important that growers pay attention to canola rotations," stresses Hammond.

For blackleg, where varietal resistance is the main control option, growing resistant varieties under short rotations selects for the most virulent strains of the fungus. The disease can eventually overcome the resistance mechanism.

"A one-in-four canola rotation combined with good sanitation practices is very effective in limiting the spread and buildup of new strains of a disease, like blackleg, and new diseases, like clubroot," says Hammond.

The impact of a diverse crop rotation on weeds is partly due to differences in crop competitiveness, which prevents shifts in the weed spectrum within a field. For example, a high canola frequency in a field will favour cruciferous weeds. Growing cereals in the rotation, however, can shift the spectrum to more grassy weeds. Another great benefit of a diverse crop rotation is the opportunity to use a range of different herbicides not used in canola, providing improved overall weed control in the long term. The use of different herbicide groups also helps prevent the buildup of resistant weeds. However, he cautions growers to be sensitive to re-cropping restrictions and potential herbicide residue problems as they plan rotations.

Diverse crop rotations also provide other benefits. Rotating crops with different rooting systems and depths can result in improved water use efficiency for the farm. A combination of cereals, oilseeds, pulses and forages results in a variety of crop residues that can improve soil aggregation and nutrient cycling. As well, yields for the entire farm will tend to be more stable.

"The bottom line: A well planned crop rotation can reduce pest pressure, leading to improved yields, less reliance and use of chemical controls, and improved farm profitability," says Hammond.