Co-written by Dr. Lori Phillips, AAFC Harrow
Multicropping practices like double cropping and relay intercropping hold the promise of increased productivity and profitability through the harvest of two crops per year on the same acres of land. Double cropping in southern Ontario is not a new practice; farmers in Essex, Kent and Lambton have for some time seeded soybeans after an early winter wheat harvest. Recently this practice has become even more common with the expansion of winter canola acres in these counties. Combining a successful winter canola harvest with favorable fall conditions for soybean grain filling can lead to highly profitable outcomes. However, in regions with shorter growing seasons, such as central Ontario, double cropping becomes less reliable. Here, relay intercropping presents a viable alternative, offering farmers a way to reap the benefits of multicropping while mitigating the risks associated with shorter growing periods.
Relay intercropping is an agricultural practice where two crops are grown together in the same field for part of their lifecycle. One crop is seeded into a standing, actively growing crop before it reaches maturity. The first crop is harvested while the second continues to grow and is harvested later. This system makes better use of sunlight, which is often underutilized during the shorter seasons in traditional monocropping systems, and extends the period of ground cover, reducing soil erosion and nutrient loss.
Over the past five years, Agriculture and Agri-Food Canada’s (AAFC) Ontario Living Lab has been investigating the challenges and benefits of implementing relay intercropping on farms. At Van Meer Farms near Tillsonburg, farmer Greg Vermeersch worked alongside researchers to address production challenges while highlighting the ecosystem services provided by extended periods of living roots in the soil. In a video summary, Greg shares insights from the 2021 season. He emphasized practical considerations like centering the second crop (soybeans) between rows of winter cereals at planting (Photo 1), choosing crop pairings with height differentials to simplify combining (Photo 2), and covering parts of the cutter bar to avoid damaging the second crop during the first crop’s harvest (Photo 3). In the end, Greg’s double-crop soybeans out yielded the relay intercropped soybeans (43 vs. 40 bu/ac), a result he attributed to a late frost affecting the relay beans.
The Role of Soil Microbiology in Relay Systems
The benefits of relay intercropping extend far beyond yield, particularly in improving soil health. Research led by Dr. Lori Phillips, a soil microbiologist, examined how Greg Vermeersch’s relay intercropping practices influenced the soil microbiome on his farm. Soil samples were collected from soybean, winter cereal, and control (no cereal) rows at various points during the growing season. DNA analysis and quantitative PCR (a molecular laboratory method) were used to measure microbial processes related to carbon, nitrogen, and phosphorus cycling. The findings revealed that intercropping increased bacterial and fungal populations by 30% and 90%, respectively, while also enhancing the soil’s ability to decompose crop residues and cycle nitrogen. For instance, cellulose decomposition capacity increased by over 125% in intercropped fields, potentially improving organic matter storage in sandy soils.
Crop residues left after cereal harvest (both above and below ground) feed diverse microbes, whose biomass eventually accumulates as stable carbon in the soil. Winter cereals also supported higher populations of beneficial microbes, with nitrogen-fixing bacteria (e.g., rhizobia) increasing by 40% under rye or barley compared to non-intercropped fields. This combination of fungi breaking down crop residues and bacteria fixing atmospheric nitrogen likely contributed to the observed fivefold increase in soil organic nitrogen. Relay intercropping soybean with cereals fostered a more abundant and diverse microbial community, delivering critical ecosystem services that could enhance the long-term resilience and productivity of the agricultural system.
Adding winter canola to the mix
Profitability is without a doubt one of the key consideration for farmers looking to try relay intercropping for the first time. With this in mind, Grain Farmers of Ontario supported a collaborative research project between AAFC and the University of Guelph to examine whether winter canola, a high value oilseed, could bring additional value to a relay intercropped system with soybean. In research led by Marinda De Gier (a graduate student at the University of Guelph) winter canola was seeded in wide rows in late August/early September at four locations across southern Ontario—Elora, Woodstock, Harrow, and Woodslee. The following spring, soybeans were inter-seeded into the standing canola before bolting (Photo 4). Given that winter canola stands are known to produce dense canopies early in the spring, this research aimed to investigate how these canopies could be modified by changing the winter canola seeding density and/or the quantity of nitrogen fertilizer applied in the spring.
Results of this research clearly demonstrate that managing nitrogen inputs is essential to the success of relay intercropped system with winter canola. While spring nitrogen significantly boosted winter canola yields by an average of 0.9 Mg/ha, it reduced soybean yields due to the impact on the canola canopy. More nitrogen resulted in bigger winter canola and less resources (i.e., light, water, nutrients) for the developing soybean seedlings. In general, soybeans grown in a relay intercropped system yielded 59% less than sole crop soybeans, demonstrating the challenges of growing under a winter canola canopy. Never the less, when the total grain production in relay intercropped systems (canola + soybean) was compared to sole crop soybeans, there was no difference in the biological productivity of the cropping systems.
Economic analysis of relay intercropping with winter canola proved its potential viability, though profitability remained lower than that of sole cropping systems. Sole soybean systems achieved the highest net income, averaging $1,002 CAD per hectare, while monocrop winter canola generated $691 CAD per hectare. Relay intercropped systems produced net incomes between $443 and $579 CAD per hectare, highlighting the trade-offs associated with managing two crops simultaneously. Higher input costs, including additional planting and harvesting operations, were a primary factor reducing the economic advantage of relay intercropping. Nevertheless, the system offers advantages beyond immediate profits, including improved land-use efficiency, enhanced soil health, and diversified rotations.
For farmers considering relay intercropping, starting with small-scale trials is recommended. Adjusting nitrogen application rates, optimizing planting configurations, and refining timing for planting and harvest operations can help farmers adapt the system to their specific conditions. While challenges remain, such as managing competition and mitigating environmental risks, relay intercropping represents a promising pathway for sustainable and resilient farming in Ontario. With continued research and adoption, this innovative system has the potential to redefine multi-cropping practices and strengthen Ontario’s agricultural landscape (Photo 5).
