The Italian ryegrass (Lolium multiflorum), dormancy release and bio-indication.
See the article Ryegrass for ryegrass cultivation.
Life cycle
The Italian ryegrass is capable of germinating throughout the year as shown in the calendar below, but the quantities are not evenly distributed. The flowering and maturation periods are more limited and concentrated in the summer months.[1]
Distribution of germination over time
It is noted that 70% of individuals germinate from October to December with a clear peak in October and only 30% during the spring period. Older bibliographic references report 94% autumn emergence and only 6% in spring.
Note: In recent years, a shift and spreading of germination increasingly later in the season has been observed. This phenomenon is notably due to the selection pressure exerted by root herbicides which favors seed germination after the end of product persistence. Climate change and milder winters also favor spring ryegrass populations.
Seed characteristics
The optimal emergence depth of ryegrass is between 1 and 2 cm, with a maximum depth reaching 5 to 6 cm. Germination is rather staggered.
The TAD (annual decay rate), i.e. the quantity of seeds that can no longer germinate after one year, is quite high, 60-75% at maximum. Thus, in one year 60 seeds out of 100 can no longer germinate. If there is no soil intervention, ryegrass seeds would theoretically disappear after 3 to 5 years (hence plowing recommended every 4-5 years).
Seed dormancy release
Temperature
Temperature during the seed maturation period (July-November) is the main factor influencing dormancy of future seeds. Higher temperatures during seed maturation lead to reduced dormancy.
In detail: [3]
- In trials, plants grown in the laboratory at warm temperatures during seed development produced seeds with higher germination at maturity and after 5 months of after-ripening than seeds developed at cooler temperatures.
- The germination optimum is around 20°C.
- A warm maturation temperature reduces the number and size of seeds produced, suggesting a broader impact of temperature on seed development.
- A post-maturation temperature of 40°C is optimal for dormancy release, resulting in higher maximum germination than lower or higher temperatures. Post-maturation temperatures above 50°C reduced germination, possibly indicating a deleterious effect on seeds.
Humidity
The effect of moisture level on dormancy release of annual ryegrass is less clear than that of temperature.
Water stress during seed development had no significant effect on seed dormancy at maturity.
However, an effect of water stress appeared when combined with low temperatures. Under these conditions, seeds lost dormancy faster than watered plants. This suggests a complex interaction between temperature and moisture.
In summary, no clear correlation was found between precipitation during seed development and dormancy release rate. But a possible link between low moisture during seed development and reduced dormancy of annual ryegrass cannot be excluded.
Ryegrass, a bio-indicator weed?
As shown on the map below, ryegrass is present over much of metropolitan France and infests large crop fields at varying levels depending on the regions. Therefore, considering its presence or absence in a field has a low indicative power which is generally not taken into account[4].
Ryegrasses, a nitrophilous species
Scientific studies show that the more nitrophilous a species is (according to Ellenberg), the higher its potential aerial growth and the more its growth depends on nitrogen availability.
The ELLENBERG-N index classifies species according to their affinity for nitrogen on a scale from 1 to 9, ranking nitrophilous species between 7 and 9 and oligotrophic species between 1 and 3.
Ryegrass has an index of 8, so it is a nitrophilous plant with a strong capacity to uptake nitrogen in high availability situations allowing a rapid expansion of its leaf area. This leads to strong light interception, thus a high photosynthesis capacity as well as a better shading ability of neighboring plants.
| Label | Example weed | |
|---|---|---|
| 1 | Extremely infertile site | Rat's-tail fescue |
| 2 | Extremely infertile to more or less fertile site | Spring draba |
| 3 | More or less fertile site | Bird's-foot trefoil, rough hawkbit, soft brome, field nigella, Venus' looking-glass, summer adonis, bastard toadflax |
| 4 | More or less fertile to intermediate fertility site | Slender spurge, soft geranium, wild lettuce, false hawkweed, field hedgeparsley |
| 5 | Intermediate fertility site | Creeping bentgrass, field lady's mantle, sterile brome, cock's-foot couch, cut-leaved cranesbill |
| 6 | Intermediate to very fertile site | Field canarygrass, common ragweed, corn poppy, broadleaf plantain, false vipers bugloss, curled dock, sticky catchfly |
| 7 | Very fertile site | Tall fescue, reflective amaranth, hairy bittercress, field thistle, white goosefoot, creeping couch, common fumitory, slender geranium, purple dead-nettle, English ryegrass, green bristlegrass, rough hawkbit, Aleppo sorghum, Persian speedwell |
| 8 | Very fertile to extremely fertile site | Common thistle, cock's-foot panic, cleavers, Italian ryegrass, annual meadow-grass, common ragwort, intermediate chickweed, stinging nettle |
| 9 | Extremely fertile site | Greater burdock, dioecious nettle, broadleaf plantain |
Sources
This article was written by Jasmin Razongles, agronomy engineering student in work-study at the Centre National d'Agroécologie.
- ↑ 1.0 1.1 https://www.arvalis.fr/infos-techniques/bien-connaitre-la-biologie-du-ray-grass-pour-adapter-les-moyens-de-lutte#:~:text=Les%20ray%2Dgrass%20peuvent%20germer,et%20au%20d%C3%A9but%20du%20printemps.&text=Le%20TAD%20%C3%A9lev%C3%A9%20et%20la,d%C3%A9sherbage%20efficace%20%C3%A0%20court%20terme.
- ↑ http://www.odera-systemes.org/pdf/adventices
- ↑ https://media.ahdb.org.uk/media/Default/Imported%20Publication%20Docs/AHDB%20Cereals%20&%20Oilseeds/Weeds/WRAG/Understanding%20and%20combating%20the%20threat%20posed%20by%20rye-grass%20(Lolium%20multiflorum)%20as%20a%20weed%20of%20arable%20crops%20full%20(2010).pdf
- ↑ S.Cordeau.2023;ARE WEEDS (BIO)INDICATORS?
- ↑ https://www.agro.basf.fr/fr/cultures/ble/adventices_du_ble/ray_grass/
- ↑ Soil status characterization - are weeds (bio)indicators? - https://hal.inrae.fr/hal-04114763v1/file/tcs_122-dossier_et_page_a2c.pdf
