The Value of a Crop Rotation

  Hort Snacks - June 2018
Download 358K pdf file ("HortSnacks-June2018.pdf")PDF
     Subscribe to our free E-Newsletter, "Agri-News" (formerly RTW This Week)Agri-News
This Week
     Hort Snacks HomeHort Snacks Home
 One of the most fundamental agronomic recommendations that is applied to any crop is to ensure that an adequate crop rotation is followed. A crop rotation is defined as “the practice of growing different crops in succession on the same land…” To dive deeper into that definition, it means that you ensure that the crops you are growing potentially contribute something to, or don’t negatively impact, the other crops within the rotation. It means that not only are you growing different crops one after the other, but they are sufficiently different so as to have little or no common pests, as well as different rooting depths and fertility requirements. The overall goal of crop rotation is to ensure that the health of the soil (and the crops growing in it) is maintained, and preferably enhanced and improved over time. And rotation also means having some amount of separation between cropping areas, to prevent transfer of a problem from one area to another.

The length of a rotation can vary quite a bit and is, of course, subject to a number of factors. The general recommendation for a rotation is 3 to 4 years, with rotations sometimes stretching as much as 7 or more years. The number of years doesn’t merely represent a change in the calendar, but the separation of entire growing seasons. One of my personal pet peeves is seeing what is referred to by some as a “canola:snow” rotation, which is NOT a rotation at all, and leads to a whole host of problems (more on that later).

Over the decades, there have been countless studies that have highlighted and demonstrated the benefits of following a crop rotation. Despite the overwhelming evidence in favour of crop rotations, you might be justified in asking why some people still don’t follow this practice (see previous example “canola:snow”). The following are some reasons why agronomists recommend rotations (when at all possible), just to keep you convinced.

1) Give the soil a taste of something different
Rotations are made up of a range of different crops, although you might only be interested in a particular crop, and the rest are just filler. Regardless, each of those rotation crops brings something different, whether it is the amount of organic matter it contributes at the end of the season, nutrients (e.g. legumes), associated microorganisms, etc. Mixing up the crops helps to diversity things a bit and shakes up the soil ecosystem, in a good way.

2) Mix up that soil profile
Just as different crops contribute different nutrients and amounts of organic matter to the soil, rotational crops also typically have different rooting profiles and habits. Cereals tend to be prolific rooters, which can push organic matter deep into the profile, beyond the shallow area in which vegetable crops mainly function. Legumes might not root all that deep, but they charge up the nitrogen levels a bit. Cover crops can also stir things up by penetrating through hardpan layers, which improves water penetration and drainage, at a minimum. It is also important to not underestimate the impact of how each crop is managed, after harvest, as the required cultivation and/or soil preparations for the next crop can alter the soil profile, often to the overall benefit of the soil.

3) Interrupt those disease/pest life cycles
In order for diseases and pests to really get going and get a foothold in a crop, they need a susceptible host and suitable conditions for them to grow and develop. By interrupting disease and pest life cycles, and by removing the susceptible host, you encourage the reduction in the amount of surviving critters and disease inoculum. The longer the rotation, the more chance there is that overwintering spores and resting insect stages will be starved out, meaning you have less of an issue to deal with when you come back in with the crop later in the rotation.

4) Expand your pest management toolbox
If you are using pest management tools to control your pests, sometimes you come out ahead by controlling issues in other crops. By growing other crops, you open up your management options, and can collectively bring down the pest problems for all of the crops in the rotation. For example, you might have issues with grasshoppers, but haven’t got a lot of options in veggies, but you can control them in cereals.

5) Build up the soil – give a little back
Including nitrogen fixing legumes in a rotation has long been common practice. The use of other crops, which encourage a diverse soil microbiology, can also improve things. And mixing up the crops means that you have a chance to put different textured crop residues into the soil. All in all, a win:win outcome.

Sometimes rotating can be challenging to plan, but once you commit to it, it should flow pretty smoothly. And no one says that you have to farm all of the rotational crops; they can be farmed out to a renter. The end message is that rotating between crops should be of more benefit to you than not rotating, other than maybe simplicity or rough economics. Give it a try.

Share via
For more information about the content of this document, contact Robert Spencer.
This information published to the web on May 29, 2018.