Features Agronomy Soil
Canola crop rotations could condition northern soils

Field crop rotations tested in a greenhouse setting at Algoma University revealed that organisms in the soil can be coached to contribute to higher yields if crops are grown in specific rotations. For best canola crop results, ideal rotations include canola-corn-soybeans-alfalfa and canola-alfalfa-corn-alfalfa.     Photo by Photos courtesy of Pedro Antunes, Algoma University.

Not that long ago, farmers didn’t know planting bacteria with soybean seed produces better crops. There could be hundreds of equally critical underground interactions farmers don’t know about, but at least some progress has now been made by studying canola.

Dr. Pedro Antunes, a researcher at Algoma University in Sault Ste. Marie, Ont., says canola associates with a huge diversity of fungi and bacteria, viruses, and also larger living organisms much like every plant that grows in soil. His studies indicate, however, that certain crop rotations condition the soil’s biota to work with canola better than other plants because of the sequence of plant characteristics canola has, that lead to the greatest difference between beneficial and antagonistic biota. Antunes says plant roots are constantly exuding sugars and organic compounds which attract or deter different organisms, leading to a process called soil biota feedback, and he has gathered evidence supporting this that could explain his results.

“The way that a plant influences the soil has consequences for its own success and that of other plants,” Antunes says. “If we’re talking about agriculture, then this is going to influence the competition of plants in the field: it has consequences for how plants interact with weeds and, also importantly, it will affect plants that are coming in after.”

Researchers like Antunes have questions about the biodiversity in soils and how that biodiversity influences plant growth, nutrient availability and general crop quality.  These questions inspired the controlled environment study.  In a greenhouse setting, alfalfa, canola, corn, soybeans and wheat were rotated through pots of typical northern Ontario soil. Once the potted sterilized and unsterilized field soil had been “trained” by the initial crop over 10 weeks, crop rotations were simulated (that is, each plant grew in its own trained soil and in soil trained by all other plants). In order to gain conclusive evidence of the impact of soil organisms, Antunes said the later crops had to be grown again in all combinations of trained sterilized and unsterilized soil and in untrained sterilized soil that was only inoculated with a small portion of the previously trained unsterilized field soil to control for soil fertility.  As a result, his team found that, for instance, canola grew 20 per cent more after alfalfa than a repeat canola crop, and they were able to gain insight into the contribution of soil biota to these growth increments.

“So this approach allows you to choose the best kind of crop rotation to get maximum yield, including taking into account plant-soil biotic interactions,” he says. “Though we have to be cautious because these are findings from a greenhouse experiment.”

In the real world, there are even more variables to impact the interactions between soil microbes and plants. Antunes is eager to start multi-year plot trials in the field to confirm his top recommended rotations for northern canola production which are canola-corn-soybean-alfalfa or canola-alfalfa-corn-alfalfa. Although his research has extensive application, focusing on canola for the Algoma district was timely for regional farmers.

“Most people do hay, there’s cattle and a little corn, and not too many field crops because of challenges imposed by soil drainage and the climate,” Antunes says. “However, there’s much potential for farming in northern Ontario and to try out new crops.”

David Thompson, research project co-ordinator with the Rural Agri-Innovation Network (RAIN) based in Sault Ste. Marie, helped to secure funding for Antunes’ research. Thompson says with the unreliable nature of beef prices and a slow decline of dairy in the area, farmers have been looking to expand their operations. With a new cold press oilseed crushing plant recently established in nearby Bruce Mines, the association has taken an active interest in canola research.

“In our area, we haven’t seen many cash crops like soybeans and canola in recent years, there are only a few farmers who are actually trying it,” Thompson says. “We wanted a project that helped farmers understand the conditions and the techniques that you would use for growing canola.”

RAIN was established to support applied research projects that meet the needs of local producers and encourage farmers to try new things. But Antunes says that in addition to providing data specifically about canola production to Algoma district farmers, he has already collected enough data to attract a wider audience. “This work is novel, not just for northern Ontario, but has potential applications globally, because we have very poor knowledge of soil biota,” he notes. “These biota, they form soils, maintain soil aggregate stability, they are soil engineers. And if we don’t understand what they’re doing belowground, then we can’t capture the benefits that they can provide.”

Antunes suspects unravelling the secrets of soil biota could be significant in improving soil health. To begin answering the scientific questions that Antunes alone thinks of would require armies of researchers. In the meantime, he believes his work is a starting point for researchers to better understand and build on what farmers already know about crop rotations in general.

“There’s a lot of empirical knowledge that farmers use based on word of mouth and we had a hard time finding any criteria for the design of crop rotations,” he explains. “So the first thing we did was publish a review paper on the sets of criteria that could be used.” ("Accounting for soil biotic effects on soil health and crop productivity in the design of crop rotations.” Journal of the Science of Food and Agriculture: Volume 95, Issue 3, pages 447–454, February 2015.)

Antunes has high hopes future research will identify the many individual organisms and their roles in the soil, while also contributing towards more sustainable agriculture that is still capable of offering higher yields in canola and other cash crops grown around the world.

March 31, 2015  By Amy Petherick