Decreasing agricultural diversity could affect sustainability.
“The trend is toward simplification of our systems with fewer crops dominating the landscape,” said Bill Deen of the University of Guelph.
Why it matters: More diverse crop rotations can improve soil health while boosting yields and long-term sustainability.
He and other scientists are studying the importance of longer crop rotations for soil health and improved productivity, yet some farmers are going in the opposite direction.
Simple rotations are more prevalent because they are more profitable for the producer.
“Everyone agrees soil health is a concern but the management practices associated with that problem are not feasible economically,” Deen said at a recent agrologists meeting in Alberta.
Farmers know this, said Agriculture Canada researcher Yantai Gan, who works at Swift Current, Sask.
“Crop rotation is a centuries-old concept. Some farmers look at the profitability and the market first to decide, and not really look at their longer term soil health,” he said.
Profitability is not a bad thing but diversification has a longer-term benefit.
“Farmers look at the markets first and I agree with that because you want to make money. But you do have other choices,” he said.
Soybeans are dominating in Ontario, said Deen.
Between 1970-2014 more soybeans were planted while corn, winter wheat and hay acres have decreased.
His work involves testing long-term simple and complex rotations at the University of Guelph research station in Elora.
Corn and soybean rotations have resulted in lower yields, decreased soil organic matter, poor soil structure and higher nitrogen requirements.
As the climate continues to change, different planting strategies may be needed because poor rotations may lead to water shortages.
The growing area of Ontario’s Great Lakes basin can expect drier, hotter summers with more winter precipitation, similar to what is predicted for the Prairies.
Fifty years’ worth of data found water demands go up as corn yields increase.
Breeding a better plant is not the answer.
“If you want more yield, you have to transpire more water. If we increase our corn yields in the last 20 years by 40 or 50 per cent, we need more water to produce that,” Deen said.
Well-planned rotations are associated with soil organic matter buildup and water retention.
Gan’s work looks at the semi-arid regions where diversifying crops with pulses like peas, lentils and chickpeas increase productivity while decreasing the environmental impact.
In a 10-year study, his team has experimented with continuous cropping and rotations with cereals, oilseeds and pulses to assess yield and soil health.
“We learned that diversification and rotations of the crops is the very key to make that farmer more profitable, more sustainable and more resilient over time,” he said.
They measure how each crop takes up water and the depths roots go to pick up moisture. They also measure nutrients in the different rotation systems as well as the diversity of bacteria and fungi communities in the soil.
“If you continuous crop with canola or wheat you will probably decrease the water holding capacity. The reason for that is when you use the same crop year over year the rooting profiles are the same. The use of water and use of the nutrients in the soil profile stay the same every year,” he said.
Diseases can increase with shorter rotations. Lentils and peas fix nitrogen but fungal pathogens can build up in the soil if continuously cropped.
Weeds may increase and build up a seed bank in the soil if a crop is continuously grown. If crops are diversified either by species or variety, different approaches can be used to keep weeds back and prevent them from building up resistance to herbicides.
Gan came from China and worked in the northeast where soybeans dominated.
“Those regions used to be soybeans but they are no longer able to grow soybeans because they used soybean-soybean-soybean and with the fungal buildup in the soil, you can no longer grow soybeans,” he said.
“Eventually the monoculture will catch up with what you are doing.”