Intercropping can boost profits and provide agronomic benefits. But before jumping in feet first, farmers need to think through the process
Intercropping involves growing two or more cash crops in the same field. Farmers may also grow a cover crop over green manure. While some might assume intercropping is more suited to organic production, that’s not the case.
“Under these conventional systems, with the right crop combination, you would get over-yielding,” says Dr. Martin Entz of the University of Manitoba. Over-yielding occurs when the two crops yield more grain than a single crop would have yielded on the same land.
Entz and his colleagues have researched intercropping in both organic and conventional systems. Ten years ago PhD student Tony Szumigalski studied several crop combinations under organic and conventional systems.
On average, pesticide-free crops got a yield boost from intercropping 47 per cent of the time, while conventional crops over-yielded 75 per cent of the time. Canola-pea was the best performer during the three-year study. Pesticide-free canola-pea over-yielded 67 per cent of the time, while the conventional version over-yielded 100 per cent of the time.
Intercropping on the farm
Colin Rosengren, a Midale, Sask. farmer, started looking into alternative cropping systems in 2004. Today half or more of Rosengren’s 5,000 acres are intercropped every year. Intercropping boosts Rosengren’s net returns by increasing yield, and, in many cases, lowering inputs such as fungicide. Rosengren also sees less insect damage in some intercrops.
Rosengren grows specialty varieties such as maple peas, which are sold into the racing pigeon market in the U.S. He says maple peas have poor standability, poor yield and are disease prone. But when they’re grown with canola, “they stand up perfectly fine, they don’t get diseased, and we find they yield the same as yellows. And we get paid more.”
Andy Kirschenman farms near Hilda, Alta. Kirschenman uses cover crops to establish green manures, and he is also growing 600 acres of mustard-canola this year.
“I like the idea of a yellow mustard because it isn’t as susceptible to some of the insects as canola is. If we can stay out of the field with some of the insecticides, I’d be happy,” says Kirschenman.
1. Crop choices
Farmers should pick two crops that will mature at roughly the same time, or can wait while the other crop matures.
Entz, Rosengren and Kirschenman all say pea-canola or pea-mustard are good choices for first time intercroppers.
“It’s very forgiving. Both crops are very easy to harvest. I mean the feeder house thrashes both of them out, so that’s a good one to start with. It also has shown consistent positive results,” says Rosengren of pea-canola.
Choosing a late-maturing pea and early-maturing canola will help the crops mature at roughly the same time, Rosengren says.
Flax and chickpeas are also a winning combination on the Rosengren farm, cutting ascochyta and boosting flax yields. Rosengren says he won’t grow chickpeas without putting flax with them.
In general, Entz and his colleagues haven’t seen a great yield response with wheat, which he says was initially disappointing. He says he thinks it may be because wheat is less plastic than some other crops, and yield is set early.
“One thing we did find is… you really reduce the diseases in the wheat when you intercrop it,” says Entz.
Rosengren has also tried peas and wheat, and flax and durum. “Typically anything with cereals we’ve struggled to get much of a gain by intercropping.”
Kirschenman has tried wheat-flax too, but finds the wheat is too competitive and the maturity gap too large for it to work well.
“What has worked well has been Clearfield canola with sweet clover underseeded to it,” says Kirschenman, who’s been growing this combination for four years.
Farmers in Kirschenman’s area include fallow fields in their rotations. The year after seeding, Kirschenman allows the sweet clover to grow into late June before terminating it. In areas with more moisture, he thinks producers could seed warm-season cereals into it, or swath-graze it.
Farmers can seed each crop in its own row, known as strip intercropping, or mix the crops.
Entz says research out of India and the tropics shows strip intercropping often works better than mixed rows, but that’s not the case for every crop. For example, when lentils are seeded at a 45-degree angle to flax, they suppress weeds in flax, Entz says.
Kirschenman has seeded clover and canola in separate rows, which worked, but left him with 15-inch gaps in the next year’s clover. He now seeds it in mixed rows.
“You probably get more benefits of the intercrop early in the season that way because you do have that root interaction… It takes quite a while to grow across 7-1/2 inches, which was what our alternating rows were,” says Kirschenman.
Rosengren has had the best results seeding mixed rows rather than alternating rows for most intercrop combinations, including peas and canola. But when it comes to chickpeas and flax, Rosengren seeds two chickpea rows, then two flax rows, on 7-1/2 inch spacing. He seeds it against the wind, so the flax stops ascochyta spores from spreading.
Seeding rates are often set at two-thirds the regular rate, but that can vary. Both Rosengren and Kirschenman set their pea-oilseed crops at two-thirds the full rates.
Generally Rosengren is trying to bring up canola yields, but peas will out-compete canola, so he seeds the peas deeper to give the canola a head start on emergence. Usually each crop yields about two-thirds of a full crop, giving him a yield bonus.
Seeding rates with chickpeas and flax are a little trickier to nail down because of the micorrhiza fungi on the flax roots. Rosengren thinks the micorrhiza connect the flax roots to the better-rooting chickpeas, allowing the flax roots to find more nutrients.
Last year Rosengren seeded 15 pounds of flax per acre. A typical full rate for his farm is 50 pounds. Normally he would apply 60 pounds of nitrogen with the flax, but he didn’t lay down any. But the flax still yielded 90 per cent of an average monoculture flax crop, says Rosengren.
“We grow specialty flax that’s been $18 a bushel. So if we’re growing 20 bushel flax and 20 bushel chickpeas like last year, that’s amazing.”
Kirschenman seeds the clover and canola at the same time. He sets seeding depth at the correct depth for the smallest seeded crop. Canola is seeded at the regular rate, and he sets the clover at three to four pounds per acre.
When it comes to fertilizing pea-canola, Rosengren takes the inoculant into account. On soil with low organic matter, the best results he’s seen come from applying about two-thirds the nitrogen of a typical canola crop.
Though there is no direct link between the rhizobia inoculant and canola, the rhizobia will break down nutrients in the soil, freeing up more nitrogen if there’s plenty of organic matter. So Rosengren applies less nitrogen to soil with high organic matter, as long as mineralization is likely.
Kirschenman uses a little less nitrogen, but a full phosphate rate, for pea-mustard. He lays down nearly a full nitrogen rate for canola-clover. “The benefits of the green manure are mostly coming in the years after, not in the year of establishment.”
Intercropping systems can control weeds, says Entz. But they’re really good at clamping a lid on disease.
“The problem with raising yields in monocrops is you raise these incredibly dense canopies that are very humid. Even in dry areas they stay humid longer during the day. So there is a lot more potential for disease infestation. And so the question that we’ve been asking ourselves is how do you create a real high-yield situation, but not have so much disease pressure,” says Entz. He says creating diversity within the canopy is one answer.
In some cases, intercrops seem to deter pests. Entz cites research out of North Dakota showing flea beetle infestations were less severe in canola-pea intercrops than monocropped canola.
“Some of the benefits that we’re seeing, in some years may be due to disease. In other years, they may be due to insects that we didn’t observe. And in some years, maybe it’s a combination of all those things plus more photosynthetic capture,” says Entz.
Rosengren has found that although spraying Odyssey in-crop doesn’t normally damage peas, the peas don’t always recover when they’re competing with canola. One year after he sprayed Odyssey, damaging the peas, “it cost us 10 bushels an acre in pea yield, but we gained seven in canola. So in the end it netted the same dollars.”
The flax-chickpeas intercrop sees far less ascochyta blight than monocropped chickpea, says Rosengren.
When other farmers are spraying their chickpeas for the fourth time, Rosengren says, “we’re starting to think about our first pass.”
Kirschenman can spray Odyssey, Pursuit or Solo in the canola-clover intercrop without damaging the clover. He also uses a Group 3, such as Edge, with the pea-mustard to control Group 2 and glyphosate-resistant kochia.
When it comes to harvesting lentils and flax, farmers should take care not to chip lentils during threshing. Entz says the lentil chips are the same size as flax seeds, making it difficult to separate them.
“Those sorts of practical things are really important to keep in mind,” says Entz.
Kirschenman says the canola-clover intercrop is usually easy to harvest. An early frost might set the canola back, and there have been a couple times where the clover is as tall as the canola during harvest. But Kirschenman says the canola does dry out in the swath.
“It doesn’t take that long and then you’re able to harvest it just as you would straight canola,” he says.
Based on his neighbour’s experience, the peas-mustard should mature at the same time, Kirschenman says. He plans to use a rotary cleaner to separate the seed. “You’re able to through-put at least a 1,000 bushels an hour, but probably more.”
Rosengren straight-cuts both the flax-chickpea crop and the canola-pea crop. Swathing pea-canola works, too. The crop is cut high enough that there is still stubble to anchor it against big winds. The swaths are heavier, too, so they’re less likely to tangle. Rosengren cautions a canola-lentil swath blows around easily. The lentils also lay at the swath bottom, which is a problem if it rains.
When it comes to harvesting the flax-chickpea crop, Rosengren sets his combine for chickpeas. He says it’s simple to harvest them, but there needs to be at least five bushels per acre of chickpeas for threshing.
Rosengren likes to separate the seeds from both crops right away, but he says if they’re dry, they can be stored for a while. He’s used rotary drums to separate the seeds, and says they worked well. But he now uses a rotary cleaner with shaking screens, as it’s a little more reliable and has more capacity.
Entz says farmers have asked whether growing a canola intercrop, such as pea-canola, means growing monocropped canola later in the rotation would increase disease risk. He says more research is needed before he can give a good answer, but he thinks farmers’ experiences are important.
“I don’t think the threat is serious enough to not consider intercropping. I think intercropping is intriguing and is worth a try. And I think as we gain more experience with it, hopefully we’ll get some pathologists starting to look at these cropping systems a bit more closely and provide those answers in the future,” says Entz.
Rosengren says he wouldn’t follow pea-canola with canola, but in his opinion disease has more to do with how intensely a crop is grown in an area than rotations in individual fields.
“This is not the opinion of most researchers I talk with but it has been my experience,” Rosengren writes.
Kirschenman says he isn’t concerned about disease pressure from short intercrop rotations.
“Short duration rotations are really not an issue for us because we’re trying to get into six and seven year rotations. So even if it is an issue, it’s not going to be an issue for us.”
Andy Kirschenman blogs about his on-farm trials and other production practices at andgronomy.blogspot.ca. Research by Entz and his colleagues is available online at umanitoba.ca/outreach/naturalagriculture/.