Full-Crop Rotations Gain Momentum

EDMONTON - Jan 14/04 - SNS -- Western Canadian farmers are thinking more often in terms of full crop rotation cycles instead of just worrying about year to year changes in what is seeded, helping them do a better job of managing disease and weed cycles on their land.

"It's always interesting to hear farmers talk about their crop rotations," says Don Wentz, agronomist, Reduced Tillage LINKAGES, Lethbridge. "Instead of saying this is a new spring wheat variety or a new herbicide-tolerant canola, they are saying this is canola-on-wheat stubble or wheat after peas. Farmers are thinking of crop production in terms of full-crop rotations and not just from year-to-year."

Rotating crop types, such as oilseeds followed by cereals, or cereals following pulses, can help control disease and weeds, and give bigger yields.

"With the many herbicide-tolerant canola varieties available today, crop sequencing is very important," says Wentz. "Herbicide carryover can be good or bad depending on the circumstances, and growers should always consider how soil texture, pH, organic matter and moisture conditions will affect it. A big advantage to including herbicide-tolerant crops in a rotation is that it allows for a change in herbicide groups to reduce herbicide-tolerant weeds."

Crop-disease interactions are another important consideration when setting up a crop rotation. Rotating crops can reduce soil-borne diseases resulting in increased yield. "For example, we know that canola and peas are susceptible to sclerotinia," notes Wentz.

"If canola is planted on pea stubble, there is usually less plant material to infect the next crop. As well, there is a foliar spray available for sclerotinia control on canola but not on peas. On the other hand, sclerotinia affects peas less than canola, and later in the season. As such, if we have grown peas on canola stubble or vice-versa, we should follow with a cereal to break the sclerotinia disease cycle."

The question now becomes whether this follow-up cereal should be barley or wheat. "Peas and lentils are legumes and therefore convert and store atmospheric nitrogen in the soil. Research shows that soil residual nitrogen is also about 20 per cent higher in pea stubble than in wheat stubble. However, if the barley is going for malt, the protein content may be too high following peas," says Wentz.

"In this case, wheat would be the better choice. Pulse crops like peas and lentils are shallower rooting than cereals and oilseeds. Research has shown that pea and lentil stubble has about 10 per cent more soil moisture than does wheat, mustard or chickpeas. Wheat yields about 25 per cent more when grown on pulse stubble than when planted on wheat stubble. This is similar to the increase when canola is seeded on a pulse stubble."

Another issue around crop sequencing and rotation is the method of seeding, and whether to use a low-disturbance (LDS) disk opener or a high-disturbance (HDS) hoe opener. "In each case, direct seeding into the previous year's crop residue is possible," says Wentz.

"Note that direct-seeding research has shown that, no matter what the soil disturbance level was, weed growth is reduced in all cases with a Roundup pre-seed application. Research also shows that LDS has fewer weeds and a quicker start for the crop than the HDS."

However, adds Wentz, soil type, crop residue, stones and other factors determine what seeding opener works best for each area. "Bottom line is whichever one gets the crop out of the ground first wins."

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