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2019-003: Plant-soil interactions and stand decline in alfalfa: Mechanisms and potential mitigation strategies

Researcher: Jonathan Bennet

Funding; $55,936

Project Description:

Plant mixes and polycultures have gained increasing interest from producers over the past several years. Many producers are also interested in how to maintain a healthy stand, and are curious as to whether winterkill and overgrazing are the only definitive reasons why some stands don’t persist. Jonathan Bennett, a plant scientist from the University of Saskatchewan, will work to understand how a single crop stand and how multiple plants in a crop stand age, as well as their influences on soil microbes and it’s productivity. As alfalfa suffers from multiple root diseases with unknown causes, the SCA Board was interested in potential solutions this research might bring.


In order to understand legume decline over time in plant stands, this team sampled soil microbiome in 24 alfalfa monocultures and alfalfa-grass mixtures that were between one and six years old. They had four alfalfa varieties, and included six other forage species (sainfoin, red clover, American vetch, purple prairie clover, crested wheatgrass, and northern wheatgrass).

They found that some alfalfa varieties, namely Brett Young 3010, can take advantage of older pasture soils - that variety increased its growth by 36% due to the presence of specific arbuscular mycorrhizal fungi in the soil.

Sainfoin grew 35% better in grass-alfalfa mixtures than in sterile soil, likely due to the presence of certain beneficial bacteria in those soils (not rhizobia). Conversely, red clover grew better and had more nodules in alfalfa seed production soils suggesting that it can take advantage of alfalfa associated rhizobia in those fields but doesn’t do as well if those rhizobia are diluted, as in mixed stands.

Combined this suggests that certain alfalfa varieties and sainfoin may be better choices for rejuvenating pasture than red clover because they are helped by the microbiome in these fields.

Native plant species did poorly when inoculated with microbes from weedy fields, likely due to shared pathogens, suggesting that if you are seeding native species, pre-seeding weed management may be critical.

However, more tests are underway or in the planning stages.

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