With grain prices in the basement and crop inputs staying high, many farmers are looking for that one piece of magic to make the whole system work. There is no piece of magic. The system works when all the pieces are put into place and managed. In direct seeding we often talk about the 5 pillars: Residue Management, Fertility, Weed Control, Rotations, and Crop Establishment.
Crop Rotation is defined as a planned sequence of crops. The key is the "planned sequence". I have seen rotations that are market oriented or very haphazard. This type of rotation usually ends up costing you more money in the long run with either higher inputs or the loss of some of the rotation benefits that can be achieved. The rotation of crops has an impact on residues, weed control and fertility.
Many direct seeders are using a 4-year crop rotation with a Cereal - Pulse - Cereal - Oilseed. This rotation can be used in all soil zones, although the specific crops that are plugged into the rotation will vary according to the region. The advantages to this rotation include:
Over the next few issues of the Prairie Steward, I will be addressing all of these issues of rotations and how they impact one another. In this issue I will look at the weed control aspect of this rotation.
All weeds have a time of year or a specific climatic condition in which they germinate and grow best. If we always seed the field closest to home first and the field furthest away last, we are selecting for specific weeds on these fields with our seeding habits. One of the best examples of this is Pygmy flower and Yellow Whitlow grass. These weeds germinate as soon as the snow leaves, flower 2 to 3 weeks later and have produced seed before the end of May. If you always seed this field last, you have allowed these weeds to go through their entire life cycle without any disturbance. Using a crop rotation to determine the time of seeding will vary the seeding date on each field as you rotate the crop on that field. Low residue stubble such as pulse or oilseed stubble should be seeded first as it will warm up sooner and also dry out quicker due to the lower amount of residue covering the soil. Higher residue fields such as cereal stubble will hold the moisture longer and will also take longer to warm up in the spring so they can be seeded later and still have adequate moisture for crop germination.
When controlling weeds in crop there should be a basic plan. Herbicide rotation should be considered. It is usually cheaper to control broad leaf weeds in a cereal crop and grassy weeds in a broad leaf crop. So this is where the emphasis should be placed. One example is a little bit of Buckwheat in a cereal crop. It may not seem economical to spray it out this year but the seed set from those weeds will make it necessary to control the buckwheat in the broad leaf crop the next year. The cost of controlling the buckwheat in a wheat crop is much cheaper than in a pea crop or a chickpea crop where there is no registered control.
Residual herbicides should be used to your advantage but require rotation planning and a good set of field records. Don't sacrifice your rotation because you used a herbicide with recropping restrictions that doesn't fit into your rotation, regardless of how good the weed control it will give you.
Perennial weed control is best achieved with preharvest applications of glyphosate. Once again, planning your rotation will give you the opportunity to control these tough perennials in the crop so harvest and weed staging work together. Many farmers do not like to use preharvest in canola because they feel the damage from the sprayer is more than acceptable. Pulses should be a good candidate for preharvest as the Roundup will also help dry down the crop for harvest. The problem in pulse crops is that when you have high thistle populations, the pulses are not competitive and where the thistles are, you have no crop at all. Many farmers like to control the perennial weeds before they plant their pulse crops. That leaves cereal crops for the preharvest application. But if you are trying for malt barley the maltsters don't want glyphosate residues on the barley. Therefore, preharvest should be used on the other cereal crops and flax. An additional benefit to spraying Roundup on flax is that it stops the flax from continuing to grow and thereby saves moisture for the next year's crop.
Chart #1 shows this basic rotation with seeding dates and time of some weed control. If Preharvest Roundup is applied to the cereal crop in year 4 for perennial weed control, you can then assess the control in the oilseed crop in year 1 of the chart. If there is still a large number of perennial weeds in the field you have the option of using a post harvest Roundup application after crops such as canola or mustard are harvested. These crops are usually cut early in the fall and quite high, leaving many of the thistles leaves on the plants. With fall rains and adequate regrowth showing on the weeds, Postharvest is an option that has worked well. It is more effective to hit perennial weeds with Roundup two falls in a row (for instance, preharvest in Year 1 and post harvest in Year 2) than to wait for 2 or 3 years.
Control of winter annual weeds like Stinkweed, Flixweed and Narrow Leaved Hawksbeard also need to be part of your rotation plan. Fall 2,4-D is an excellent method of controlling these weeds. In this rotation there is a fall 2,4-D application following the oilseed and pulse crops. This is because these crops have dark residues and low residues and in the spring these fields are infested the worst with winter annuals because they will get an early start next spring. A fall application of 2,4-D is not recommended prior to seeding oilseed or pulse crops the following spring.
Chart # 1 shows the timing of all the practices I have been mentioning. However when I start plugging specific crops into this rotation I will change some of the timings:
If peas are my pulse, I will seed them first. Even though the peas are on cereal stubble, they require a lot of moisture to germinate and can tolerate cool soils. When peas are seeded early, there is usually 2 weeks before they emerge. This is an opportunity to do a post seeding-pre emergent burn off. Quite often in a Low Disturbance system, if the broad leaf weeds are controlled at this time there is very little new germination and there may not be a need to use any incrop broad leaf weed control; provided all the tough-to-kill broad leaf weeds that were in the cereal crop the previous year were controlled. This may not always work but when you build it into your rotation system you reap the benefits when it does work.
If I were using a Roundup Ready Canola as my oilseed crop I would also seed it early and not use the Zero Incorporated Granular herbicide. The reason for planting this type of canola early is that I don't need to wait for the first flush of weeds to emerge before I apply my Roundup burnoff. I can spray Roundup at any time the weeds are there and not hurt the crop. By seeding early I can also make use of the moisture and avoid the July heat.
As you can see, even though I have set out a basic rotation, once specific crops are identified, some of the practices change. There is no perfect rotation or recipe that will work for all conditions. However, a well planned and managed rotation will give you some agronomic benefits that should also help the bottom line on the balance sheet.
Chart#1