The allelopathy effect: how it can benefit organics

Research has found that roots and residues from previous crops can inhibit pathogens, such as decomposing rye residues inhibiting fusarium root rot in beans.  |  File photo

Some crops affect others by releasing chemical compounds, which could be beneficial to organic producers for weed and disease control

SWIFT CURRENT, Sask. — The idea that some crops affect others by releasing chemical compounds, and what that could mean for weed and disease control, is under study at the Swift Current Research Centre.

Allelopathy, as this is known, is difficult to observe and separate from other factors that might be affecting crops planted together, said Agriculture Canada research scientist Myriam Fernandez.

Chemicals isolated and used in laboratories often don’t work, she said, yet people have long sown plants together, or far apart, because of the observed effects of species on each other.

She told a low input and organic workshop last month that allelopathy is a tool producers could use to manage Canada thistle and other weeds, as well as diseases.

More field research is required, however, because most work has been done in labs or greenhouses.

Fernandez noted that while 2016 was very wet and 2017 was very dry, there were still high levels of fusarium root rot in pea and lentil crops last year.

“We believe that organic production based on intensive legume cropping for nitrogen supply might not be sustainable under a scenario of variable weather that includes rainy and warm growing seasons,” Fernandez said. “Allelopathy could be a solution to this issue, in addition to weed control.”

Previous research has found that roots and residues from previous crops can inhibit pathogens. For example, decomposing rye and oat residues can inhibit fusarium root rot in beans, and some brassicas control other pathogens.

“Other publications indicate the severity of aphanomyces root rot (in peas) was lower when brassicas or grasses were incorporated into the soil,” she said.

One trial underway at Swift Current is examining the allelopathic potential of different cover crops and residues to control the spread of perennial thistle. The work was done in the field and the greenhouse; the results of the field studies are not complete.

Hairy vetch, spring rye and tillage radish are known to have allelopathic potential, said Fernandez, while forage pea does not.

These crops were grown until flowering and then terminated, and the residues were either incorporated into the soil or left as mulch.

Canada thistle roots were cut into 2.5-centimetre pieces and planted into pots with the soils.

Fernandez said the forage pea treatment had the highest biomass and the most Canada thistle shoots whether the pea had been incorporated or left as mulch.

“Hairy vetch residue had the highest nitrogen content, and thistles in the hairy vetch treatment had a higher level (of nitrogen), especially when residues were incorporated,” she said.

Thistle in the spring rye treatment had lower nitrogen levels.

“Our conclusion is that, despite the higher percentage of nitrogen, the lower biomass that we saw in Canada thistles when grown with hairy vetch residues than when grown with forage pea residues indicates a greater inhibition by hairy vetch, likely due to allelopathy, and this appears to be overriding a nitrogen effect on the growth of the thistles,” said Fernandez. “Forage pea will likely increase the growth of Canada thistles just because of the nitrogen release.”

The study continues for two more years.

Producers interested in allelopathy can observe the field trials at the planned Aug. 1 field day.

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