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What is the best stubble for flax?

Achieving consistently high flax yields is a challenge, but fine-tuning the crop rotation is a way for growers to improve their chances. “One of our big goals in working with flax agronomy is trying to understand why it is so difficult to push yields to provide consistently higher grain yields. If we could consistently be in the 30 to 35 bushels per acre range, then with the right price structure, I think we could sustain a larger number of flax acres,” says Dr. Guy Lafond of Agriculture and Agri-Food Canada (AAFC).

As part of his research into production systems, Lafond has been growing flax every year for his 25 years at AAFC’s Indian Head Research Farm. So he has lots of experience in seeing just how variable flax yields can be, even in plot studies.

He says, “When you look at cropping practices and agronomic factors, usually there are two or three that account for 80 or 85 percent of the variability. We’ve done many studies trying to uncover what those factors are for flax. We’ve had multi-location and multi-factor studies, and after all was said and done, we can say a few things, but it still eludes us as to why we cannot get consistently better, more stable yields.”

Crop rotation was one of the factors examined in some of these studies. Lafond notes, “The effect of the crop stubble type on flax yields had not been really looked at before. We already had these multi-year rotational studies underway, so it was just a matter of carrying through for one additional year and to see if we could pick up the effects on flax yields of the stubble from the previous year or two years previous.”

These studies point to some rotational options that can increase the likelihood of better flax yields; not hard and fast rules, but factors to add into the mix of the things to consider when planning a crop rotation. “Cereal stubble is probably the best stubble for flax,” says Lafond. “At the same time, producers have to be careful about volunteer cereals because they can really outcompete flax, especially volunteer barley. Seeding flax on pea stubble can produce good yields but not as consistently as flax on cereal stubble. We do see benefits of seeding flax on cereal stubble where the cereal had followed a grain legume like field pea in the previous year.”

In one study, flax, as well as all the other crops in the study, had very good yields in Year 3 when the Year-1 crop was barley silage. Lafond speculates, “It could be because, with barley silage, you’re removing 90 percent or more of the above-ground residues, so it makes for a cleaner seeding environment but more importantly, an easier seeding environment.”

Research results show flax typically does not do well after canola. “If you seed flax on canola, you can almost guarantee yourself a poor crop for a couple of reasons,” he explains.

One is that flax depends strongly on mycorrhizal fungi in the soil to bring nutrients like phosphorus back to the plant’s roots. Because canola is not a mycorrhizae host, it does not leave behind a network of mycorrhizal strands capable of colonizing the new flax roots early in the season. As a result, the young flax plants have a tough time getting all the nutrients they need. Crops like wheat, barley, corn and pulses are mycorrhizae hosts and are more likely to leave behind a mycorrhizal network for the next crop. Lafond adds, “The other reason that canola before flax can be a problem is that volunteer canola can be very challenging to control in flax, and once canola gets going it’s a very aggressive plant.”

As well, Lafond’s research indicates that canola’s negative impacts on flax can sometimes persist for two years. “It’s not always a consistent effect, but it’s consistent enough to say that maybe one year after canola is not enough, maybe you need two years.”

Growing flax immediately after flax is also not recommended. He says, “Flax-on-flax is definitely a no-show; the results on that are pretty consistent. It just doesn’t thrive as it does on something like a cereal stubble.”

More tips for better flax yields
“We know that if a flax crop starts strongly in the spring it seems to carry through. If it has a difficult start for whatever reason, it seems to struggle all the way through,” says Lafond.

The choice of crop stubble type is one way to give a flax crop a better start. He recommends two other practices: increase seeding rate; and seed flax in between rows of 12- to 14-inch stubble. Lafond says the flax seeding rate should be high enough to ensure a plant population of at least 300 plants per square metre. “When I talk to farmers, most of them are using seeding rates around 40 lbs per acre. In our work with high seeding rates (60 lbs per acre), we were achieving that threshold plant population only 73 percent of the time, and at 40 lbs per acre, we were only achieving that threshold about 60 percent of the time. So you need to use about 60 lbs per acre to make sure you are over that minimum threshold. You can go higher; 400 or 450 plants per square metre won’t have a negative effect on yield.“

Getting above that 300-plant threshold is important for two reasons, explains Lafond. “Higher plant populations help accelerate crop maturity, and they are better able to compete against weeds.”

According to Lafond, flax yields could be improved by seeding between the rows of tall stubble because the stubble ameliorates the growing conditions. AAFC researchers at Swift Current have found that tall stubble greatly reduces wind speeds, lowers moisture stress and somewhat increases the air temperature near the soil surface. That microclimate helps young plants to do better. “I think there are tremendous gains to be made for flax production and this concept really needs to be tested properly in controlled field trials,” says Lafond.

He adds, “To me this concept of tall stubble and seeding between the rows is one of the most exciting areas in dryland farming. It has far-reaching implications, not just for increased yields. If you can seed into tall stubble successfully, you might be able to use a little wider row-spacings, which reduces the amount of draft as you’re going through the field. And when you cut your stubble taller, you don’t put as much residue through the combine, so you are substantially reducing energy use and tremendously increasing the combine’s productivity. When you start tying all these things together, it gets pretty interesting.”

Lafond worries about the future of flax if the challenge of achieving consistently higher yields is not met. “I am very concerned that flax may drop off the radar where people will just not grow it because other better yielding crops have displaced it,” he says. “Flax is a very good end product in the human nutrition field, it’s good in the industrial field, and it has tremendous animal health benefits when included in small amounts in rations. And there’s nothing like crop diversity in our cropping systems to maintain resiliency and as part of an overall risk management package.”