Features Environment
Productive and sustainable cropping systems

Matching carefully designed cropping system approaches with best management practices can help growers optimize crop productivity at the same time as improve whole-farm sustainability and resiliency. Researchers and industry are interested in understanding how those cropping systems might also help growers adapt to climate change, improve soil health and environmental footprints. 

“Across the Prairies, several researchers have a very large project underway comparing different cropping systems in terms of agronomics, productivity, economics and their capacity for sustainability and resiliency,” says Reynald Lemke, research scientist with Agriculture and Agri-Food Canada in Saskatoon. “We are trying to see if there are different approaches in terms of crop choice, crop sequence and other management strategies that might better prepare growers for addressing climate change and weather extremes, enhancing system productivity and resiliency across the Prairies. I’m leading the carbon footprinting component of this study, although I’m also involved with other aspects. This study was funded through the Integrated Crop Agronomy Cluster.” 

The study was conducted at seven ecosites across Alberta, Saskatchewan and Manitoba, comparing different cropping systems and six or more treatments at each site over four years. The goal of this large project was to compare cropping system approaches that would optimize agro ecosystem productivity, resilience and sustainability in major Canadian ecozones. Cropping systems include conventional, intensified, diversified, market driven, high-risk high-reward and a soil health-focused system. 

“For these systems, the actual crops and crop sequences varied depending on the soil zone or region of the site,” explains Lemke. “Each site had a reference or conventional system considered to be more typical of each location, an intensified cropping system that included pulses or oilseeds or both and a diversified system with four different crops in each year of the four-year cropping system. For example, at Swift Current, Sask., the reference system was fallow-durum-malt, barley-durum sequence, the intensified system was lentil-durum-chickpea-durum and the diversified system was lentil-canola-pea-durum. By comparison, at Beaverlodge, Alta., the reference system was wheat-pea-wheat-canola, the intensified system was wheat-canola-wheat-canola and the diversified system was pea-winter, wheat-faba, bean-canola. A soil-health cropping system focused on maximizing biomass and included a green manure such as faba bean in sequence. Each of the seven ecosites had their own specific systems.”

For the market driven or flexible cropping system, site managers selected the crop each year based on current commodity prices and the best economic outcome for that system. The management strategy was focused on maximizing yield, including bumping N fertilizer by about 20 per cent over standard practice. The N fertilizer strategy for all of the other systems, except for the reference, was based on soil test recommendations and a reasonable yield target. The reference system used a standard practice fertilizer rate for the selected crop, not accounting for residual soil N in the fall. The fertilizer management practices directly impact the carbon footprint of the cropping systems. 

Carbon footprint of cropping systems
“We have completed the first four-year cropping system sequences and plan to continue to maintain these systems for another two or three cycles in order to be able to measure the outcomes and system changes for various factors and indexes,” says Lemke. “For the carbon footprint component, the key measures for calculating the footprint are the addition of greenhouse gas emissions and change in soil carbon. The net results or balance of the equation will indicate whether the system is having a positive impact by sequestering carbon and removing carbon dioxide (CO2) from the atmosphere, or negative and still contributing to the atmosphere.” 

Lemke emphasizes that the results so far are preliminary, with some of the impacts not expected to be fully realized for a few years. “The greenhouse gas emissions observed so far confirm what we expected with higher emissions at the sites with higher soil carbon, such as the black or dark gray soils at Beaverlodge, Lacombe and Melfort compared to lower emissions in the dark brown to brown soils at Swift Current or Lethbridge. Sites with higher soil organic carbon have higher yield potential and better moisture conditions, therefore higher fertilizer use, all of which leads toward higher greenhouse gas emissions. However, although higher, the emissions overall were still fairly low.” 

For the greenhouse gas emissions calculations, direct and indirect (emissions associated with nitrogen losses through leaching and volatilization) nitrous oxide emissions (N2O) from fertilizer use and CO2 emissions from the fossil fuel use for fertilizer production, transport and delivery and from farming practices such as seeding and harvesting were included. The N2O emissions, which are of significant concern, were converted to CO2 equivalents for comparison. For context, in terms of global warming, in the atmosphere, one molecule of N2O has the same impact as nearly 300 molecules of CO2, the reason so much attention is focused on N2O emissions.

“Our early results show there were differences in terms of total emissions with the various cropping systems. Generally, the diversified cropping systems tended to have the lowest emissions, which is largely a reflection of the frequency of pulses in rotation and lower N fertilizer inputs,” adds Lemke. “The number of times a pulse appears in the four year rotation can indicate where the system will rank in terms of emissions. The market-driven system had the highest emissions.” 

To estimate the change in soil carbon, researchers relied on using a modelling approach and tools that are well established and validated for Prairie conditions. However, soil carbon changes are small and take time, so what is observed in the short-term may differ over longer time frames. In this study, the preliminary modelling results show all of the cropping systems showed an increase in soil carbon at all of the sites, some sites were small while others were more substantial.

“Overall, when putting all of the measures together, the preliminary results show all of the systems tended to have a negative carbon footprint, essentially withdrawing carbon from the atmosphere and sequestering it as soil carbon, however, some systems at some sites did have a small positive footprint,” says Lemke. “Generally, the more diversified cropping system with a pulse crop will have a better carbon footprint. There are many different considerations when looking at these cropping systems beyond carbon footprints and it will be important to weigh them against various factors, such as whole-farm economics, environmental impacts, soil health indicators to find the balance and realize the real benefits for sustainability and resiliency. As more results and information become available for the many components of this large study, they will be shared and made available.”