When it comes to canola harvest, timing is everything, says Harry Brook, crop specialist with Alberta Agriculture and Rural Development. Farmers, he says, are mostly concerned about green seed, since green seeds contain more chlorophyll and are therefore undesirable to processors. If timing is so important, how do you know when is the right time?
Although it’s not foolproof, the easiest way to tell if your canola crop is ready for harvest is to look at the visual clues. Before swathing (or combining), the crop should reach an average seed moisture content of 30 to 40 per cent.
When scouting fields, look for colour changes. Specifically, swathing decisions should be made based on the seed colour changes on the plant’s main stem, says Brook. Depending on the cultivar, when they reach that point they will turn from green to light yellow, reddish brown or brown. While the most mature seeds in the bottom third of the stem will have completely changed colour, the seed in the top pods will still be green — firm, but not squishy, he says.
Look around your fields, says Brook. When the majority of the crop is mature, it’s time to harvest. Of course, final decisions will depend heavily on how many acres you have and how long it will take you to harvest those acres.
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Potential yield loss
Harvesting too late or too early can result in yield loss, says Brook. Swathing too early when only zero to 10 per cent of seed colour change has occurred can lead to a 10 per cent yield loss. If only 10 to 20 per cent of seeds have changed colour, you risk a five per cent yield loss. Finally, harvest too late and you leave yourself open to all sorts of problems, including shattering, which can lead to significant yield losses as well.
Getting the crop off at the right time can be tough if the operation has too many acres to swath. “I’ve seen a huge consolidation in acreages here, so the farms just keep getting bigger,” says Brook. “The problem with that is the time squeeze of getting the crop in and getting the crop off. So anything they can do to speed up harvest, they’ll do.”
A lot of growers, he says, are switching from swathing to straight combining. It can sometimes, but not always, be quicker and can result in less shattering.
Consider the weather
Ideal timing isn’t just about the crop itself, though. There are other factors to consider, says Brook, like disease, pod damage that occurred earlier in the season and weather conditions at the time of harvest. The ideal weather, he says, is warm, but not too warm.
“Anything over 25 C is too hot,” he says. “The crop will dry down too quickly.” Under normal conditions, canola will lose about 1.5 per cent moisture content per day. Depending on the weather, it can lose as much as three per cent per day. If conditions are too hot, though, the crop can lose moisture content even quicker than that.
“That’s when you get the problems with the green seed,” he says.
Really high winds pose a danger, too, says Brook. “Two years ago we had some big winds come from an unusual direction. It wasn’t northwest or southeast,” he says. “That’s why you’ll often see swathing done in a northwest to southeast direction, because they’re trying to go parallel to the prevailing winds to avoid the swath moving.”
If the crop does move and get blown around in the wind, he says, the result can be very high harvest losses.
Avoid frost damage
Lastly, frost can damage crops, creating green seed issues, as well. If green seed is frozen that green colour is fixed (since freezing permanently deactivates the enzymes responsible for removing chlorophyll from the seed).
If frost is predicted, swath two to three days early, if possible, says Brook. If frost is predicted before the crop is mature, all is not lost. Moisture from rain, he says, can sometimes reactivate those enzymes, reducing chlorophyll and, therefore, green seed. Yield losses depend heavily on the degree of frost, plus its duration.
Timing for straight cutting
Shawn Senko, agronomy specialist with the Canola Council of Canada warns that timing is somewhat different for farmers considering switching from swathing to straight combining. Farmers, he says, are choosing direct harvesting for a number of reasons, but mostly because they already straight cut other cereal crops.
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“The plants would have to be fully mature and the seed dried down to around 10 per cent for direct harvesting,” he says, “whereas with swathing it is generally done at 50 to 60 seed colour change.”
Since combining eliminates the need for swathing, time can be gained, but depending on the weather, the crop may still need to be harvested at the same time either way, Senko says.