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Start planning spring crop rotations

Strong crop rotations can bring along a wealth of long-term agronomic benefits

Crop rotations can be used to take advantage of differences in how each crop in a rotation contributes to increased soil organic matter, aids in pest management, manages soil nutrients and controls soil erosion. Rotating different crops in the same field can effectively promote sustainable crop production.

If you haven’t already started planning your crops and crop rotations for next year, now is a great time to start the planning process to make changes to improve your rotations.

To get started, make a list of the goals you would like to achieve on your farm. Some of these might include:

  1. Improve profits by growing higher value or higher yielding crops.
  2. Increase soil organic matter and improve soil quality.
  3. Break disease cycles.
  4. Plant more diverse crops to rotate herbicide groups and improve weed control.
  5. Increase residual soil nitrogen release for subsequent crops by growing legumes or cover crops.
  6. Plant more diverse crops to spread out seeding and harvest for efficient use of labour and equipment.

Your goals will help you sort out the types of crops and rotations you might want to develop. Make sure newly selected crops can be successfully grown on your farm. Keep in mind important environmental considerations such as growing season length, heat requirements and water requirements. Decide approximately how many acres of each crop you want to grow.

Make a list of all your fields or draw a map of all the land you will crop next year. For each field, record the previous crops grown to avoid growing the same crops back to back. If herbicides with potential residue carry-over were used on any land in the past two years, record this to ensure a residue sensitive crop is not grown. If serious or difficult to control weeds are present in any fields indicate this. Note any other significant potential problems, such as saline soil areas, acid soils or depressional or wet areas in each field. Avoid pulse crops on strongly acid soils. Field areas that are slightly saline can be cropped to barley but large saline field areas might be better seeded to salt-tolerant forages.

A two-year rotation such as a “wheat, canola” rotation is really not a true crop rotation. Ideally, I prefer to see at least a four-year crop rotation. An example of a four-year rotation is: “pea, spring wheat, canola, malt barley” to maximize positive crop interactions.

Growing wheat after pea will take advantage of residual nitrogen release from pea residue and remaining sub-soil moisture, because pea is a shallow rooted crop. These factors will contribute to higher wheat yields and higher grain protein. Wheat grown between pea and canola will help to break common diseases such as sclerotinia. Canola is a very good scavenger of nutrients such as nitrogen. Growing barley after a good yielding canola crop means lower spring soil nitrogen levels, which will help to ensure medium protein levels in the following malt barley crop. Pea does well when seeded early and is a shorter season crop. This would help spread out harvest. Substituting winter wheat for spring wheat would further spread out labour and equipment use. This rotation means cereal crops would not be grown back to back, helping reduce disease issues. Also, pea and canola will not be grown back-to-back.

I like to see forages in a rotation. Forages build soil structure and improve soil organic matter. But, farmers that do not have cattle often only want to grow annual crops that are more profitable.

Benefits of sound rotations

Sound rotations are important for reducing pest problems. Rotating crops will help control less mobile insects and reduce the presence of residue-borne fungal and bacterial diseases. Having a break of several years between crops susceptible to the same disease will reduce disease potential.

Long-term rotations that include annual crops and perennial forages are ideal. Forages are excellent for lowering disease risk of annual crops in a long-term rotation, and also reduce the presence of weeds. Forage crops also help improve soil quality.

Shorter-term rotations using annual crops should include at least three crop types such as cereal, oilseed and pulse crops. Ideally, don’t grow the same crop more than once every four years. Don’t grow different crops susceptible to the same disease back to back. Sequence crops to your advantage. After growing a nitrogen-fixing crop such as pea, then grow spring or durum wheat to take advantage of nitrogen release to increase grain protein.

Alternating winter wheat and spring wheat helps disrupt the life cycle of weeds to help control weed problems. Rotating crops makes it easier to rotate different herbicide groups to reduce the potential of developing herbicide resistant weeds.

About the author

Columnist

Ross H. McKenzie, PhD, P. Ag., is a former agronomy research scientist. He conducted soil and crop research with Alberta Agriculture for 38 years. He has also been an adjunct professor at the University of Lethbridge since 1993, teaching four-year soil management and irrigation science courses.

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