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Careful With Your Lentil Rotation

For Maurice Berry, who farms 4,900 acres near Carievale in southeastern Saskatchewan, preventing disease and resistant weeds are foremost on his mind as he rotates his crops. On his no-till farm, he sticks to the basic four-year rotation — sometimes bumping it up to five years by throwing flax in. But with the recent high prices for lentils, Berry admits “it was hard to resist the urge to shorten the rotations.”

The biggest reason farmers ignore the suggested rotation schedule is economic. They want to grow profitable crops more often. Makes sense. Dale Risula, provincial specialty crops specialist with Saskatchewan Ministry of Agriculture, says shortening rotations may work out as long as the grower closely monitors disease levels and pays attention to regional climate. A wet season means more risk of disease than a dry one, so if you’re in a region more likely to have a wet season, the short rotation is that much riskier.

Risula’s general recommendation is the four-year cereal-pulse-cereal-oilseed rotation.

The primary benefit of crop rotation is disease control. If you plant lentils too frequently, inoculum of the disease organisms build up in the soil. Diseases that primarily affect lentils tend to be fungus-related organisms — especially ascochyta and anthracnose — with spores that stay in the soil. The more spores in the soil, the greater the disease risk for the crop and the higher the probability that mutations will occur and a more virulent strain of disease will result. Then new treatments or new strains of lentils need to be developed.

The pathogens do degrade/ decompose within the soil system over time because of other factors, for instance deterioration from sunlight or from the organisms of decomposition. If left long enough, they can decline to an acceptable level. That is why you rotate crops to manage disease.

A farmer planting lentils for the first time on a field that’s away from any other fields where lentils have been previously grown probably has a lower level of risk because the pathogens are usually host-specific — they won’t be found in the soil if the host has never been planted there. But that lower level of risk does not make jumping into two-or three-year rotations of lentils a safer practice. Years of experience and research show that shortened rotations will cause problems, even if you’re planting lentils for the first time, Risula says.

The diseases that affect lentils can have an impact when the plants are very young right up until they are beginning to ripen. They may affect yield or quality or both. Ascochyta is the most prevalent and the most damaging. Anthracnose is a close second. There are some other organisms that cause root-rot but seed treatments have been able to deal with most of them. In terms of treating lentil diseases on the Prairies, Risula feels we’ve gone quite far fairly quickly.

WEED CONTROL AND OTHER BENEFITS

While minimizing disease and pest issues is foremost in Risula’s mind, crop rotation has other benefits. For instance, producers may want to rotate plants that utilize moisture from different soil depths. Lentil roots are short so they take moisture from just below the surface. Wheat has a slightly deeper root. Forage crops, corn, and sunflowers are deep rooted.

John Bennett uses crop rotation to accomplish many objectives — to control weeds and disease, to manage nitrogen and moisture. Bennett has a no-till operation in the Biggar, Sask., where he’s farmed for 30 years.

“My sense is that lentil-durumlentil-durum is not a lot unlike wheat -canola-wheat -canola. You’re setting yourself up for disease,” Bennett says. “Plus you’re becoming too dependent on too few herbicides.”

His four-year rotation enables him to use the full spectrum of herbicides. This lessens the opportunities for resistant weeds to occur. It also prevents any possibility of residues building up in the soil.

There is some debate that no-till needs a longer rotation. Some believe that tillage aids in speeding up the decomposition of pathogenic organisms since the soil warms up more, while non-tilled soils are cooler and the organisms of decomposition are less active so pathogens are able to survive better and longer. Dale Risula says research shows “no significant difference.”

Bennett runs a four-or five-year rotation, which mirrors the general recommendation: cereal, pulse, cereal, oilseed. For the five-year rotation, he introduces a chemfallow year between the cereal and oilseed if he has a weed issue.

Bennett usually plants canola for the oilseed rotation and follows it with barley. The two crops have compatible weed control. He can easily control grassy weeds in canola but not broadleaf weeds. When barley follows canola, he has an excellent opportunity to control broadleaf weeds. He doesn’t plant barley after a pulse crop because there’s too much nitrogen in the soil and that builds up the protein in the barley, making it less likely to be accepted as malt.

On the barley stubble, Bennett plants lentils since volunteer barley in lentils is not an issue like it is with wheat. Wheat seed is hard to separate from lentils and the crop will be downgraded. Barley is easily separated from lentils.

Lentils switch out easily with peas since they both fix nitrogen and are susceptible to the same weeds. Unlike lentils or malt barley, which will be kicked down a class with any wheat content, peas can be planted on wheat stubble because the wheat seed separates out well.

Any leftover nitrogen from the canola crop is used up in the barley crop, and now the lentils will fix their own nitrogen. Bennett finds that he usually has good weed control going into the lentil rotation since most weed issues have been addressed earlier in the rotation — during the chemfallow, canola, and barley rotations.

On the lentil stubble, Bennett seeds wheat. The wheat receives slow-releasing nitrogen from the lentil crop, which ups the protein level and, in this case, increases the crop’s value.

Bennett may introduce a chemfallow year after the wheat and before the canola. He always puts chemfallow on cereal stubble, which he leaves very tall — 12 inches — so that it retains snow and reduces evaporation. Pulse residues aren’t as effective in this regard because they decompose quickly. After the chemfallow year, it’s back to canola.

While Bennett’s system weaves together moisture, nitrogen, disease, and weed management, it also has to factor in economics. What Bennett has found over years of experience is that with a good, diverse rotation, “somewhere in the mix, you always have something that is going to be a high value crop.” He doesn’t feel it’s worth skewing your rotation away from what makes sense agronomically because “you never know, if you chase a market and the market changes, then what are you left?”

Patty Milligan lives on a farm near Bon Accord, Alta.

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Patty Milligan is a freelance writer based at Bon Accord, Alta.

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