Consumer demand for organic products is growing in Canada. In order to stay competitive, meet the growing demand, and drive growth in both national and international markets, the organic industry must continue to grow, learn, and adapt.
Although there is no one clear-cut approach on how to improve the sustainability and resilience of organic production, implementation of certain practices can help organic producers work towards those objectives. Dr. Myriam Fernandez, a scientist for Agriculture and Agri-Food Canada, is determined to help Canadian organic production practices become more sustainable and resilient through science. She has dedicated more than 20 years to organic research and works very closely with farmers and industry.
With every finding, it is continuously becoming more apparent to Dr. Fernandez how interconnected an agroecosystem really is and, in particular, how sensitive an agroecosystem can be to farm management decisions. This is reflected in some of her most recent projects, which investigate cropping strategies to improve the sustainability of organic crop production in the Brown soil zone in the Prairies, as well as biological control and management of significant crop diseases.
Traditionally, legumes, such as forage peas, have been grown as a monocrop green manure in Western Canada to provide nitrogen, build soil quality, and control weeds. However, Fernandez believes that over time, organic-based production systems using intensive legume cropping for nitrogen supply are unsustainable. This is due to a number of reasons. The first is that, compared to many other species, such as grasses, legumes decompose more rapidly, and they do not contribute as much organic matter. Additionally, legume diseases have been increasing, including root diseases. A common disease, Fusarium root rot, which may be found in legumes in the semi-arid region can reduce biomass, yield, and nodulation rates, thereby also reducing nitrogen fixation.
Fernandez and her team decided to explore other practices, such as using other cover crops and intercropping. At the time, there was very little information and literature available specific to the semiarid regions of western Canada, or even to other semi-arid parts of the world. In fact, there was great disbelief that cover cropping and intercropping practices could be successful in these regions. However, the opposite is proving to be true.
The main objective of Fernandez’s recent cover cropping project was to investigate the viability of cropping systems under organic management, including cover crop mixtures grown as green manure in rotation with grain crops. The team explored ways to maintain or improve grain quality and yield, as well as soil quality. Crop growth and quality were evaluated by taking samples of biomass, recording grain yield, and sampling the harvested grain, while soil was tested both before and after growing the cover crops.
The study examined four different cover crop blends that incorporate multiple species from different functional groups (e.g., grasses, brassicas, legumes, forbs). Each blend focused on a different functional group (Table 1). The species that were selected over the years were highly compatible with the local semi-arid growing region. Choosing species adapted to the region from different functional groups was found to be a successful method when creating blends.
Cover crops can help increase organic matter, suppress weeds and pests, improve yield, mitigate disease, and reduce the need for tillage. As a result, the use of cover crops can improve the productivity and sustainability of organic systems, as well as increase overall resilience to the impacts of extreme climate events.
Although the selected blends are well suited to this semi-arid environment, farmers from other areas within Canada can also benefit from the project findings as drought and the effects of climate change are becoming more common across the country.
When selecting cover crops or intercrops, one must consider the competitive nature of the species being used, and their competitive ability when grown in different mixtures. A farmer should choose species that are well-adapted to their growing conditions. Finding the right variety and species can take time, especially under variable environmental conditions. Stay up to date, not only with organic production practices in general, but also with information shared on practices that may help with carbon sequestration and the mitigation of climate change.
DIGGING DEEPER
It is important to look beyond the cover crops themselves and see what is happening underground. This provides insight into the microbial communities, as well as diseases that may affect the cash crop that follows.
As mentioned, legumes are quite susceptible to root rot, even when grown in a dry environment. The most common grain legumes that are grown in the semi-arid region are field peas, forage peas, and lentils, all of which are very susceptible.
One of the main objectives in the crop disease project was to identify other legume species that could be more resistant to root rot. Notably, the clovers in the experimental mixtures as listed in Table. 1, did not do very well under very dry conditions, however they did prove to be more resistant to Fusarium root rot.
To study this, root samples were taken from every legume, grown as a monocrop or in a blend. The microbial community on the roots was analyzed, including the pathogens responsible for root rot. The interactions of these organisms were examined, both with themselves and with the pathogens.
Some of the Fusarium species that were found in crop roots can cause Fusarium head blight, which is a devastating disease of cereals, particularly for durum wheat. This highlights the importance of looking underground and considering the cash crop that might follow the cover crop.
Looking at what is underground, and at what promotes the growth and persistence of those organisms over time can lead to better management of disease development in the following crop. Remember that each growing combination can result in very different outcomes. For example, when intercropping, oats and field peas interact differently than mustard and lentils. Oats and field peas, despite being different species, tend to share some of the same pathogens. In regard to yellow mustard and lentils, the opposite was found to be true; mustard, a brassica, is known for being a biofumigant, resulting in an increased presence of biocontrol agents. As a result, when yellow mustard and lentils are grown together, the level of root rot in lentils was reduced. Also, in the following crop (durum wheat), there was a higher control of root rot due to the previous lentil-mustard intercrop. That being said, there are still other factors to consider when using brassicas, as they can take up considerable amounts of soil nitrogen, which can result in less available N for the following crop.
Future work will continue to investigate disease, the knowledge of intercropping, and cover crop blends, and will improve upon best management practices through research.
(OSC3) Originally published in Organic Science Canada magazine, Issue #5, Spring 2023
