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Changing crop rotations

With more and more farmers using shorter rotations, the December Manitoba Agronomists conference was titled, “Are crop rotations obsolete?”

Even with good commodity prices, farmers need high profits to meet the rising costs of machinery, land and other inputs. In some cases, agronomists are concerned that the need for cash in the short run might be straining long-term rotations.

Crop insurance data

Doug Wilcox, research manager, Manitoba Agriculture Services Corporation (MASC), has looked deep into the Manitoba crop insurance data. He examined records for fields bigger than 120 acres between 1982 and 1993.

Wilcox found that wheat seeded on wheat stubble yielded 90 per cent of average wheat yields. Canola on canola yielded only 93 per cent of the average canola yield.

Although MASC has the authority to deny coverage for improper rotations, Wilcox says, “We usually don’t.” While farmer and commodity advocate groups like to see good agronomic practices, none of them are asking for government program administrators to add agronomic requirements.

Even without restrictions on insurance coverage, in the long run, farmers who consistently grow lower yields will benefit less from insurance payouts due to two factors built into the crop insurance program. First, after several years with lower yields, a farmer’s individual productivity index (IPI) will lower the insured yield on the farm. Second, farmers with frequent claims will pay more for insurance premiums due to the discount/surcharge system.

Driving factors

At the Manitoba Agronomists Conference, Anastasia Kubinec, MAFRI’s oilseed crop specialist, gave away the ending to her presentation with the title: “What drive$ Manitoba Crop Rotation?”

She told the audience that crop rotations have changed over the past 10 to 20 years, and that “dollars” are what’s driving a lot of this.

In 1992, 53 per cent of Manitoba farmland was seeded to wheat. Now, wheat acreage has dropped to 30 per cent; canola has climbed to 36 per cent of total acreage.

Like Wilcox, Kubinec has been sifting through the MASC data. She’s found that, since 2000, incidents of farmers seeding wheat on wheat stubble have decreased. However, there has been a slight increase in farmers seeding wheat in a rotation with a one-year break (that is, wheat, something else, wheat). Based on data, fields where a three-year break is used have the highest potential yield.

As well as in an increase in farmers taking just one-year breaks between seeding canola crops, Kubinec found a slight increase in canola grown on canola stubble. In practice, use of the “best” agronomic rotation (a three-year break) is decreasing.

What does Kubinec think is driving this move to shorter rotations, despite the best agronomic advice? Prices. If you’re making money, she says, “of course you’re going to keep on growing that crop. And maybe a little bit more for good measure.”

Some of the dangers of short rotations are not obvious. Contaminants from past crops can impact returns in the future. Kubinec says, “You get a few soybeans in your dry beans, and it’s become a food contaminant.” When it comes to herbicide tolerant crops, volunteers can easily become hart-to-manage weeds.

Kubinec mentioned a number of things for farmers to consider when planning rotations:

  •  Consider the rooting depth of the crops you’re planting from one year to the next. Canola and wheat have the “exact same rooting depth, and they take up about the exact amount of moisture.” Below that root depth, you could have salinity build up. Adding a deeper-rooted crop like corn or a sunflower to the rotation help take advantage of moisture at lower levels.
  •  It might be useful to plant oats or flax after herbicide tolerant soybeans, so you have limited concerns about weeds, disease, or herbicide residue.
  •  Be careful about planting flax after canola. Both of these crops use mycorrhizae for phosphorus uptake. After canola, your mycorrhizae populations will be reduced.
  •  After you grow sunflowers, you need at least a three-year break to reduce the potential for basal rot, mid-stalk rot and head rot.

Kubinec is concerned about farmers’ long-term profitability. While our rottions are driven by our expectations about net returns, she says, “to actually get those returns, we need to make sure we retain our yield potentials.”

“We need to take into consideration all the things that happen with crop rotation, to keep our returns high.”

Evolving understanding

Dr. Dwayne Beck, South Dakota State University also spoke on the subject of crop rotations.

“Much of the research and management we do is devoted to optimizing a single component” — like yield, said Beck.

Beck stressed that we can’t rely on new technology to solve all of our problems (like herbicide resistance), or “it’s just going to be an arms race.”

Prairie farmers have made many changes to tillage practices. Beck reminded agronomists that, “if we’re going to take tillage out, then we have to replace it with other culture practices, such as rotation, sanitation and competition.” †

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