Integrating cover crops into forage operations is becoming a popular strategy to improve soil and offer a diverse diet to livestock.
Growing multiple crops together is also known as polycropping, polycultures and cocktail mixtures.
Jillian Bainard, a research scientist with Agriculture Canada at Swift Current, Sask., said producers believe benefits include enhanced weed control, better soil health and greater productivity.
These are short rotation crops and can produce large amounts of biomass and extend the grazing season. They can also interrupt disease and weed cycles.
The first cover crop trials at Swift Current started in 2013 to assess the benefits.
While this part of southwestern Saskatchewan is a semi-arid region, researchers have noted species richness and good productivity under harsher growing conditions, especially when compared to monocultures.
The study included plots with up to 12 species in various blends.
“We see there is a positive trend, and the more species we include, we tended to see higher productivity,” she said during a recent webinar hosted by the Beef Cattle Research Council.
Mixtures that include legumes, cool and warm season grasses and brassicas such as forage turnip and radish each offer something different, including more forage production, nitrogen fixation and weed control.
A new trial was initiated in 2018 in which different mixtures were selected for certain purposes.
Forage quality and quantity can be maintained or improved when compared to a monoculture. Protein content was higher, and neutral detergent fibre was lower in mixes.
Micronutrients in the mixtures offer more calcium, copper, iron, nitrogen, phosphorus and potassium.
“You don’t want high levels of some of these, so there needs to be feed testing to make sure these are in the right balance and supplemented if necessary,” she said.
Legumes such as hairy vetch have high crude protein levels and are highly digestible. Mixtures high in brassicas may have toxic levels of nitrate and sulfur, so they should not be offered in a monoculture. However, in the right proportion, brassicas grow well after being grazed and are frost tolerant with high palatability.
Some mixtures are created for weed suppression.
Competitive plants such as brassicas with lots of leaves shade the soil and take over a larger area. Some of these crops also have the potential to release chemicals that suppress other plants around them.
“Those mixtures seem to have a better ability to control weeds than monocultures,” she said.
Different row spacings from half a foot to a foot apart were tried to assess weed growth.
“We found the row spacing did not have an impact on the weed abundance, but the species selection really did,” she said.
Oats and peas offered the poorest weed control, while barley, turnip, triticale and radish had the best weed suppression.
There are also reports of some cover crops becoming weeds, such as hairy vetch that went to seed and grew back. Management oversight can make sure some plants do not go to seed. However, some producers like that because hairy vetch is a low-growing legume that fixes nitrogen.
“Weeds can get out of control in a cover crop and especially if that cover crop performs poorly,” she said.
“In those really dry years, if you didn’t hit the seeding time right and get some biomass production, it might have been a bit of a wreck where a lot of weeds might have been able to come in there,” she said.
Producers report soil improvement with better colour, quality and texture, but that attribute has been harder to prove in research trials.
“Soil properties take a really long time to change in general,” she said.
They have not found many significant effects in the research, but more results are coming.
Grazing had no significant effect on soil chemistry after the first year of a research trial.
Changes in the living component of the soil are being checked. The fungal community composition was different under mixtures than monocultures such as oats.
“It is not better or worse, but it is different,” she said.
Grazed plots lowered bacterial diversity and increased fungal diversity the following year. Bacterial communities change rapidly because of factors such as temperature, moisture and changes in soil pH. Fungal changes occur slowly, so they could be a better indicator of a change to the living community.
There was an increase in soil-stable aggregates when growing mixtures. This is the ability of the soil to stick together.
Mixtures with increased diversity provided the greatest number of statistically significant increases in the percentage of water-stable aggregates.
More research is needed on all of these practices, and monitoring of soil quality will continue because changes may take a long time.
Researchers are planning to explore the impact of actively grazing livestock on cover crops in annual rotations. They want to move to larger scale plots to see what kind of residue is left and measure the wider impacts of grazing.
Bainard encouraged producers to talk with people who have tried cover crops and consult seed companies and extension representatives to see what works in each region. Species selection is locally dependent.
“Pick the species based on what you want them to do,” she said.
Seeding dates depend on grazing strategy, moisture and temperature. Seeding in June provides later season grazing. In a dry year, there is a risk of getting no production.
When producers are planning a cocktail mix, it is important to remember that the crop recommended by seed companies may not work in some locations. For example, kale does not grow everywhere.
There is a lot of variability because of weather and local topography. Seeding these mixtures is also challenging because the seeds come in different sizes. Look at the suppliers’ recommendations for seeding depths. It is also dependent on tillage, equipment and moisture levels.
“Depending on the type of equipment you have and if you can side-band or you can select different depths with different boxes on your seeder, that is great,” she said.