Allelopathy: The Case of Buckwheat
Allelopathy refers to the set of biochemical interactions that occur between plants, or between plants and microorganisms.
In practical terms, allelopathy is understood as a plant’s ability to release molecules that affect the growth of competing plants (weeds).
The allelopathic effect of buckwheat, described in this article, is stronger than in other plants.
Description
This phenomenon is still poorly understood because it's difficult to determine whether the reduction in weeds per square meter is due to allelopathy or competition for key growth factors (light, water, nutrients, etc.). In 2023, INRAe published a synthesis of all scientific studies on the topic dating back to the 1950s. Out of 450 publications, only 7 were able to quantify the chemical allelopathic effects of buckwheat on weeds in the field. This suggests that resource competition may still play a significant role.
Agroscope conducted pure buckwheat crop trials to determine whether the weed-suppressing effect of buckwheat was truly due to allelopathy—i.e., the release of molecules into the soil—or simply due to light competition.
In these trials focused on amaranth, its emergence was significantly limited—regardless of whether shading was light or heavy.
- "-filet" = without netting to separate buckwheat plants, resulting in high light competition.,
- "+ filet" = netting used to space out buckwheat plants, resulting in low light competition as sunlight reaches the soil directly.
It was shown that buckwheat secreted 600 additional molecules in the presence of amaranth, compared to when grown alone.
So something is indeed happening, but how can this molecule release be more precisely controlled in an agricultural production context?
Under what conditions does buckwheat’s weed-suppressing effect occur?
First of all, in the field, buckwheat sown at 40–50 kg/ha is generally cleaner (fewer weeds) than when sown at 30 kg/ha. Seeding rates above 50 kg/ha are usually avoided to reduce the risk of lodging.
Additionally, field feedback shows that this "allelopathy" only expresses itself on soils with at least minimal moisture.
When does this effect not occur?
Buckwheat-wheat intercropping
As part of the CONSERWA research project, the National Center for Agroecology (CNA) tested buckwheat-wheat intercropping. These trials were carried out under no-till (NT) systems in Eure, Haute-Marne, and Nièvre, as well as under reduced tillage in Eure.
Seeding rates ranged from 20 to 80 kg/ha, sown simultaneously with wheat. The wheat was sown at standard rates and planting time (mid-October).
Although there was no frost before late November, observations made one month after sowing (November 15) showed very poor buckwheat emergence (fewer than 15 plants/m², despite sowing rates up to 300 seeds/m²), with plants stuck at the two-leaf stage.
This is because buckwheat has a vegetative zero growth point at 6°C, meaning its development is halted below this temperature, which is commonly reached after mid-October.
Buckwheat-fennel intercropping
In this field case from Eure, buckwheat was sown at 30 kg/ha between fennel rows. Here, the buckwheat had time to develop before reaching its vegetative zero. However, only the buckwheat rows remained clean. The fennel rows experienced significant weed infestation, with no noticeable effect from the buckwheat.
Buckwheat-rapeseed intercropping
Here, the seeder had a 16 cm row spacing. Rapeseed was sown in every third row, while buckwheat was sown at 30 kg/ha in the two rows left empty between rapeseed rows. Once again, the buckwheat rows stayed relatively clean, while the non-buckwheat rows had substantial weed pressure.
Summary
To achieve a weed-suppressing effect with buckwheat, it must be sown densely, uniformly, and allowed to develop properly.
Sources
This page was written with the kind assistance of Martin Rollet, agronomist at the National Center for Agroecology.
This page was written in partnership with the Conserwa project and with the financial support of the European Union.
