Weed management is a major problem in farming. Agronomic levers such as crop rotation, false seedbeds or delayed seeding help control weeds, but ploughing remains the most effective solution.
Ploughing, a mechanical weed control solution that buries weed seeds and destroys surface weeds
The plough is a farming tool used to fight weed development in crop fields. It significantly reduces the surface seed bank, mechanically destroys germinated weeds and disrupts the development of perennial weeds.
The harmful impact of weeds on cereal crop yields is real and significant. Combining ploughing with other agronomic practices helps effectively control weed growth and spread.
Characteristics of weeds
Weeds, more commonly known as "unwanted plants", are diverse. Understanding their biology is key to controlling them.
There are 2 main categories of weeds:
- perennials
- annuals
Perennials
Perennial weed species proliferate through the fragmentation of vegetative organs: rhizomes, tuberised roots, suckers and runners.
Examples of common perennials in crops: dock, couch grass, field thistle, sow thistle, bindweed, etc.
Rumex obtusifolius, also known as bitter dock
couch grass
- These are hard to eradicate because their regenerative power is in the roots. Fragmented rhizomes give rise to new shoots.
- In addition to rapid multiplication, perennials are also unique in that they accumulate reserves in their roots, allowing survival for several years in the soil.
Annuals
These account for 80% of weed species in arable crops. Examples of annual weeds and grasses: vulpine, pigweed, poppy, goosefoot, ragwort, foxtail, ryegrass, brome, wild oat, etc.
foxtail
goosefoot
- They live for a year or less but spread rapidly via seed production.
- These seeds germinate at shallow depths (5 cm of soil), and grow rapidly.
Ploughing acts as a mechanical herbicide, especially effective on annuals.
Annual Decline Rate (ADR)
ADR measures how long the seeds stay viable in the soil. Each buried weed seed has a lifespan and germination potential. ADR estimates the percentage of seeds that lose their ability to germinate, or their viability, after one year in the soil.
Deep tillage helps prevent and manage weeds by inducing dormancy or blocking germination. Ploughing will therefore be effective against weeds with a high ADR, such as vulpine, ryegrass, wild oat or sterile brome, which have ADRs between 70 and 95%. These weed seeds quickly lose their viability once buried. If ploughing is done 2 to 3 years later, the remaining viable seeds are minimal and unlikely to germinate.
Agronomic levers for weed control
Many farmers rely on herbicides to prevent field infestations, but it’s wiser to use them as a last step in a weed control strategy. Some preventive approaches (before weeds emerge) can stop infestations without curative treatments (after they’ve appeared).
Combining tillage operations (stubble cultivation, ploughing, false seedbeds) with smart herbicide use supports long-term weed management and boosts yields.
Crop rotation and diversity
Crop rotation is a lever to control weed pressure, especially in no-till or reduced-till systems (Soil Conservation Agriculture or Simplified Cultivation Techniques).
Weed species adapt to specific crop types, for example:
- grasses thrive in wheat-maize rotations
- Ryegrass is prevalent in wheat monocultures
- Ragwort dominates in rapeseed/protein crop rotations
Incorporating a spring crop (such as maize, sunflower or peas) into a rapeseed/wheat/winter barley rotation considerably reduces the pressure from autumn-germinating grasses.
It may be worth it to use cover crops between main crops as a means of preventing weed growth. They help by shading out weeds and competing for water and nitrogen. This is especially effective when the cover crop is well-established and dense, providing good soil cover. On the other hand, if the cover crop is poorly established or underdeveloped, they are less effective at controlling weeds.
Generally speaking, longer, more diverse rotations prevent the specialisation of weed species, making control easier. It's easier to control heterogeneous weeds than a high concentration of a single species.
This alternation mainly affects autumn/spring-germinating weeds, but has limited impact on those that can germinate year-round (e.g., bluegrass and chamomile).
Staggering sowing dates
In straw cereal crops, delaying sowing reduces the germination of autumn grasses (e.g., vulpine, brome and, to a lesser extent, ryegrass), as well as poppies, cocklebur and pansies. Combining this method with ploughing improves effectiveness. Compared with sowing at the end of September, a 15-day delay can reduce infestation by more than 70%.
But delayed sowing has trade-offs. Although delaying the sowing date can lead to a reduction in the use of plant protection products (fewer aphids, fewer weeds), this method also has its drawbacks. The crop's yield potential is slightly reduced and planting conditions become more complex. The later the sowing date, the fewer days available for sowing, particularly in heavy and/or moisture-sensitive soils.
Tillage between crops
Tillage includes several agronomic levers such as false seedbeds, stubble ploughing and ploughing to manage weeds. Each operation must be considered within a sustainable weed control strategy to reduce the use of phytosanitary products.
Farming practices have varying effects on the seed bank of weeds in crop fields.
Interventions | Seed bank Reduction | Destruction | |||
|---|---|---|---|---|---|
Annual weeds | Perennial weeds | ||||
Young plants | Developped plants | ||||
Shallow stubble tillage = false seedbed | 1 pass | ||||
Several passes | |||||
Deep tillage ploughing | 1 pass | ||||
Several passes | |||||
Tillage | |||||
Highly effective | Fairly effective | Effective | Not very effective |
The effects of ploughing on weed control
Depleting the weed seed bank
85% of annual weeds germinate within the top 5 centimetres of soil. Ploughing before sowing helps bury weed seeds deeper, making them less likely to germinate. Once buried, many seeds lose their viability—this is especially true for grasses like brome.
Ploughing can eliminate up to 60% of grassy weeds, making it a useful strategy for reducing seed banks of annual grasses, brome and certain broadleaf weeds. Ploughing also breaks up perennial plants, damaging their vegetative organs and pushing them deeper into the soil.
Physically destroying young weeds and sprouts
Ploughing removes surface weeds and crop regrowth, leaving the field clean before sowing the next crop. We recommend ploughing to a maximum depth of 20 cm, which helps avoid excessive mixing of organic matter. This technique greatly reduces weed emergence in the following crop.
Reducing herbicides
In conservation agriculture or minimum tillage, the absence of ploughing often leads to more herbicide use, especially glyphosate, to control weeds and crop regrowth. The amount of glyphosate used decreases as tillage intensity increases.
By reintroducing ploughing, the need for herbicides drops, reducing the Herbicide Treatment Frequency Index (HTFI) by up to 55%. This improves economic indicators, in other words, better yields and much less chemical herbicide use over time. Certain systems—like early sowing, short rotations of autumn crops and no-tillage farming (direct drilling)—can encourage the growth of autumn-germinating weeds.
If chemical weed control fails and pressure is high, reintroducing ploughing into the crop rotation can help tackle infestations that have become unmanageable with herbicides alone.Even if the most effective herbicide targets 100% of weeds, it only controls one tenth of the potential population present in the soil over the course of a year. That’s because only 10% of the seeds present germinate each year. Using farming methods like ploughing helps decrease the overall seed bank faster.
In organic systems, weed control relies heavily on mechanical methods. Ploughing prevents seed germination and destroys existing weeds. Mechanical control can be as effective as glyphosate.
To sum up, the success of weed control depends on using the right methods, either alone or in combination, tailored to the field conditions. These agronomic levers should consider the biology of weed species, infestation history, available equipment, and the soil and climate of the region.
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