Experts look at the performance of various cover crops to determine the best mix for weed suppression and plant biomass production
SWIFT CURRENT, Sask. — The growing interest in cover crops has prompted researchers at the Semiarid Prairie Agricultural Research Centre to look for the best mixes for southwestern Saskatchewan’s drier environment.
Jillian Bainard said cocktail forage mixtures, as cover crops are also known, are believed to improve soil and forage quality.
A three-year study that began in 2013 is looking at what makes mixtures more effective and how many species the mix should contain.
The experiment is using 12 species in four groups: barley, forage oats and triticale in the cool season grasses category; corn, millet and sorghum for warm season grasses; field pea, forage pea and hairy vetch for legumes; and kale, forage radish and turnip for brassicas or root crops.
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The crops were grown in monocultures and in cocktails of two, four, eight and 12 species together. Each treatment was repeated four times in the research plots and seeded in early June. They received no fertilizer or pesticide except for a small spray in 2013 because neighbouring re-searchers were concerned about blister beetles.
The biomass from the plots was collected in late July and removed in August. The same treatments were repeated in 2014 on the same ground.
“We’re doing that to accentuate some of the impacts we might be seeing in the soil in particular,” Bainard said.
The same seeding rate was used for all species. As well, a traditional meadow brome-alfalfa traditional mix was seeded for comparison.
Bainard said the 2013 results found that kale and sorghum performed poorly, both when grown alone and in mixes. Sorghum struggled to compete against weeds, while kale emerged poorly and didn’t establish well.
She said that might be because all crops were seeded at the same depth. The kale would have preferred to be shallower.
The cool season grasses produced the most biomass in the four and eight species mixes.
“Corn did a lot better than millet or sorghum,” Bainard said. “Similarly, radish had quite a high biomass production, whereas turnip or kale had smaller.”
She said the mixtures generally outperformed the monocultures.
“You might have guessed there would be some competition or re-duction in biomass, but we didn’t actually see that,” she said.
“When we look at that biomass production over all the different treatments, it goes up with the number of species that are included.”
Bainard said she wasn’t expecting the 12-species mix to perform as well as it did.
Her analysis of fibre and crude protein didn’t find strong patterns after the first year. All mixtures did well in weed suppression, with the 12 species doing the best job.
The traditional perennial mix didn’t perform well in 2013, although Bainard noted it was the establishment year.
The repetition of the experiment in 2014 had to deal with many more weeds and nutrient-depleted soil.
“The biomass patterns were similar,” Bainard said.
“The perennial crop did very well this year.”
The legumes benefited the health of the system, as could be expected, and the treatments with more groups and species did better.
All the data hasn’t yet been analyzed, but she said even the 12-species mix struggled with more weeds this past year.
Some species contributed more to the composition of the plots. For example, peas and legumes did well while the warm season grasses were poorly represented.
For 2015, the soil will be tilled before seeding to see if the weed population can be cut back and nutrients in the soil released.
She said the evidence indicates that mixtures are useful and that species selection will be the important factor.
Economic analysis is not part of this particular project, she added, but the data will be available if collaborating researchers want to pursue the numbers.
