Intercropping done well can give both crops an advantage, provided they have just enough space to do their work
Ascochyta rabiei had resistance to strobilurins, a key management chemistry, at every site in a recent survey of the disease across the prairie chickpea growing region.
Michelle Hubbard, a research scientist at Agriculture Canada who led the survey, said the efficacy of fungicides against ascochyta is waning.
“There’s issues both with fungicide resistance and with the cost of applying fungicide, and then the risk of you could still lose your crops despite using fungicides appropriately,” Hubbard said.
She has been looking into alternative practices to try to manage diseases in Canadian chickpea crops, including intercropping.
“Intercropping in general interests me because it just makes sense. A lot of diseases can really get going in monocropped agricultural systems — where if the host is suitable, and the environment is suitable and a pathogen is present, the disease can spread and spread across a whole field of a suitable host,” Hubbard said.
Intercropping chickpea and flax is not a mainstream practice in Canada, but it is becoming more popular and it’s been an established practice on some Saskatchewan farms for many years.
Colin Rosengren has grown intercrops on his farm near Midale, Sask., since 2004, and he said the chickpea and flax combination is the best one out of all of the combinations he’s tried.
“It’s the number one at the top, no brainer. There is no other way to grow either of those two (crops),” Rosengren said.
He said the best disease control results he’s seen when growing chickpeas and flax together comes when he uses paired alternate rows, with two rows of chickpeas between two rows of flax, and ideally seeded on a northeast-southwest angle.
“What we’ve observed is that any spot where the disease starts, it doesn’t really spread. We’re creating firewalls and it greatly slows down its spread, and that’s what we’ve seen with ascochyta,” Rosengren said.
“When it (ascochyta) starts, it spreads in a great big oval the direction of the dominant winds, and when it starts to take off, it goes like wildfire across your field.”
He said the paired row of flax between every paired row of chickpeas provides a physical barrier that provides exceptional disease suppression in some years.
A chickpea monocrop will likely out yield a chickpea-flax intercrop In growing seasons with good soil moisture, low humidity and low disease pressure, Rosengren said.
“But in a year where you’ve got humidity and moisture and you’re up against disease pressure, you will probably get more chickpeas with flax than you will on your own, and you get the flax as well,” he said.
“Probably any type of wetter weather climate years, for sure, it’s a big win, and on the other years it generally is on par or a smaller win.”
Lana Shaw led a small plot trial at Redvers, Sask., in 2014, in which she found less ascochyta blight and better yields in desi and kabuli chickpeas when intercropped with flax compared to a monocrop check.
An intercropping project that Hubbard is involved with expanded on this work.
The study started in 2018 and was set to end in 2021, but it will be extended because the pandemic prevented research during the 2020 growing season.
Small plot trials were held in Saskatchewan in Swift Current, Indian Head, Redvers, Melfort and Saskatoon.
Hubbard said they chose these sites to get data from multiple eco zones.
The chickpea seeding rate was consistent while the flax seeding rate was varied. The flax was planted in the same row mixed with chickpeas, in alternate rows and paired alternate rows.
Two nitrogen rates of zero and 60 kilograms per hectare were used.
Dry conditions set the study back, but the best year for the study so far was in 2019, when all of the sites went forward except the Saskatoon site because of emergence issues due to dryness.
“In 2019, we found that in Swift Current things were really dry. So there was very little disease and hence the benefits of intercropping for disease control couldn’t really be tested,” Hubbard said.
“But in Redvers and Melfort, there was a measurable amount of disease. So we found that at some of the high points where we went and assessed disease severity, there were differences, and the intercrop plots had less disease than the monocrop plots.”
When it comes to the planting arrangement of the intercrop, each of the treatments had either the same or less disease compared to the monocrop, and at the Melfort site the mixed rows had more disease compared to the treatments that alternated double or single rows.
The microclimate within the crop canopy was also examined with the use of electronic monitors that record the temperature and the relative humidity every hour throughout the growing season.
There were differences in the microclimate, but they were not consistent.
“In some sites the intercrops were more humid than the monocrops and in another site the reverse was true. So we really need to get more years of data and try to figure out what’s going on there,” Hubbard said.
She said microclimate differences in the canopy between a chickpea crop and an intercrop could make a big difference when it comes to how ascochyta spreads.
Crop diseases tend to like moist environments, and this is especially the case with fungal diseases that are propagated by spores.
Temperature within the canopy also plays a big role with crop diseases.
Different diseases have different optimal temperatures — ascochyta blight prefers moderate temperatures in the low 20s C.
“One of the thinking behind the flax intercropping is that it could alter the microclimate, so the climate on a small scale within the canopy. One way in which it might happen is if you think about the structure or the shape of the plants, so flax are kind of a tall, skinny plant whereas chickpeas can be a bushy, dense plant,” Hubbard said.
“If the conditions are wet, it’s reasonable to think that it might be more humid in a field that’s just all chickpea, whereas if there’s some tall, skinny flax plants breaking up that chickpea, then you might have a drier environment and hence less disease.”
Rosengren gives credence to agronomic research, but he said he doesn’t require crop trial evidence to guide the decisions on his farm.
Instead, he keeps track of what returns the most money to the farm over time.
“If you look at it from the perspective of the chickpeas, the big benefit to them is obviously disease control they get.”
However, he said flax also benefits from the intercrop. It may also get a reduction in disease pressure, but the big benefit is that the crop seems to be able access nutrients better when it’s grown with chickpeas.
“We’ve seen over the years where we will grow more flax with chickpeas than we will in a monoculture beside it in the same year,” Rosengren said.
He said the Western Ag PRS Cropcaster consistently shows that flax is one of the least capable crops at acquiring nutrients from the soil, while chickpeas are the best at this.
“They’re (chickpeas) the best at getting roots down there and scavenging phosphorus and finding micronutrients and potash and obviously moisture and everything else, which is what makes them such a good dry crop,” Rosengren said.
“If you have healthy soils with good mycorrhizal levels, what we’re speculating is that we’re getting a really good tie together of the roots through that mycorrhizal fungi in the soil. And with the tied together roots, we’re essentially grafting our flax crop onto the chickpeas, getting a transfer of nitrogen and probably getting access to other nutrients as well.”
He said growers need to be careful when setting the seeding rates for the intercrop because chickpeas start off slowly and flax can take over the field fairly quickly.
For example, with many intercrops if each crop is planted at a two-thirds seeding rate, the overall crop can slightly favour one crop or the other, depending on fertility and growing conditions, but with flax and chickpea you can dramatically steer it towards one crop or the other crop,” Rosengren said.
“We make sure we hold back the seeding rate (of flax) and have fields where there’s relatively little fertility to start with in order to kind of hold that flax back enough to let the chickpeas form a crop.”
Crop prices also affect Rosengren’s chickpea-to-flax seeding ratio, and he varies the chickpea population to match the field’s topography.
However, there are limits in terms of how much the seeding rates can change because the crop is planted in paired rows and there always has to be a minimum amount of chickpea in the crop to help thresh the flax during harvest.
“Twenty-five or 30 percent of the mixture has to be chickpeas so that it’s abrasive enough to do the thrashing for you, because that’s what threshes the flax in the combine,” Rosengren said.
He said he still uses fungicides for ascochyta on more than half of his chickpea and flax crops.
“I just looked at my records and about 50 percent of the time we did one application. Normally our guideline is if a monoculture chickpea is on the fourth path, then we’re starting to hit the threshold for one (fungicide application),” Rosengren said.
When it comes to herbicides, he said he doesn’t really come up against any restrictions.
“We’ll often do Authority and then go in with Centurion, and if we have any wild oats, but I don’t like to put the traffic through because it does create that initial start for disease,” Rosengren said.
“There’s two things: the physical damage to a plant will definitely cause a starting point for disease in your chickpeas; the second is the surfactants. I really strongly feel that when the surfactants start to break down that leafy surface, you’re opening the door to get chemicals in but you’re also opening the door to let pathogens as well.”
Rosengren’s fertility program for the chickpea-flax intercrop is very simple some years because he doesn’t add any nutrients at all.
“Oftentimes with flax and chickpeas, embarrassingly enough, we do nothing. Like will apply zeros across the board and just throw the seed out there. Instead, we put our phos into our canola and into our barley and boost rates on those other fields,” Rosengren said.
“We feel that we get way bigger bang for our buck that way and create a little more available phos in the future by putting it with crops like canola that can acidify it and hopefully have higher uptake and then tie it up into the straw and hopefully cycle that to future crops.”
He said flax has very poor uptake of the phosphorus applied the same year, so there is a limited upside of putting any down with flax, and chickpeas are very efficient at finding this nutrient.
“We still want a little bit of N to start the crops off,” Rosengren said.
“But I hate trying to tell guys to put down 10 pounds of this and 20 of that because it depends so much on the rotation, soil and organic matter and just exactly what’s going on. You’ve got everything from fields that have absolutely nothing, and nothing to give during the year, to fields that had manure and has massive nutrients. I guess I’d just say we keep the fertility situation quite low to it (chickpea-flax intercrop).”