Adapting the cropping system according to the risk of weed infestation it generates
Technique characterization
Technique description
Knowing the level and nature of the risk generated by the cropping system makes it possible to implement an action plan to reduce weed pressure.
Risk assessment requires:
- identifying the main problematic weeds
- knowing the key elements of their biology (preferred emergence period, annual seed bank decline rate, etc.)
- studying the effect of the cropping system on these weeds.
One can then build an action plan limiting risky techniques and integrating various favorable techniques described in other technical sheets (choice of crops, diversification of sowing dates in the rotation, false seedbeds, smothering crops, etc.) The techniques to be implemented will depend on the short, medium and long term objectives and the constraints related to the plot.
Example of implementation
For example, if autumn sowings dominate and the autumn-emerging flora is the most problematic, the risk is high and it is necessary to consider delaying sowing dates and/or introducing spring/summer crops. Furthermore, OdERA-Systems is a tool designed by INRA and Agro-Transfert Ressources et Territoires for assessing weed risk according to cropping systems and developing action plans.
Implementation period
On established crop.
Weed pressure is lower in long and diversified rotations (diversity of species, sowing dates, available herbicides, etc.).
Short rotations (2-3 years) generally increase the risk of plot infestation which can be difficult to control (increased infestation and risk of herbicide resistance development). Agronomic levers to manage weeds apply to the rotation, but also in the technical itineraries of each crop and during the intercrop period.
Application of the technique to...
All crops
Easily generalizable
It is necessary to adapt the levers to each crop. For example, in oilseed rape, sowing is generally advanced to smother weeds, and in wheat it is delayed to avoid sowing at the peak emergence period.
All soil types
Easily generalizable
Some techniques such as mechanical weeding will not give satisfactory results in all soil types.
Easily generalizable
Regulations
Regulations can sometimes limit the use of certain techniques.
Example: the obligation to cover soil during long intercrop periods limits the possibility of false seedbeds at certain times.
Effects on cropping system sustainability
"Environmental" criteria
Effect on air quality:
- Reduction of phytosanitary emissions
- GHG emissions: VARIABLE
Effect on water quality:
Increasing due to reduced pesticide use. Effect on fossil resource consumption:
- fossil energy consumption: VARIABLE
Water: reduction of phytosanitary products if the action plan reduces herbicide use (with variable effect depending on molecules).
Air: reduction of phytosanitary products if the action plan reduces herbicide use (with variable effect depending on molecules). GHG emissions depend on the action plan implemented.
Fossil energy: depends on the action plan implemented.
Biodiversity: increase
An increase in biodiversity is expected linked to reduced herbicide use (however, limited herbicide ecotoxicity) and possible diversification of the rotation. Positive effect on soil biological activity. This increase depends on the techniques implemented to reduce infestation risk.
"Agronomic" criteria
Depends on the action plan implemented.
However, if the action plan leads to diversification of the rotation: the productivity of a long and diversified rotation is higher than the sum of the productivities of short rotations with the same crops (example: beet/wheat/oilseed rape/wheat/barley is more productive than beet/wheat on one side and oilseed rape/wheat/barley on the other).
Soil fertility
Depends on the action plan implemented and particularly on the chosen crops (diversity generally favors soil fertility).
Water stress
Depends on the action plan implemented and particularly on the chosen crops and soil tillage.
Depends on the action plan implemented and particularly on the chosen crops (crop diversity generally favors functional biodiversity).
Active substance durability: Increase
The action plan mainly relies on agronomic levers and involves reduced herbicide use. Therefore, herbicide resistance development is expected to be reduced.
Weed flora diversity: Increase
Introducing new crops in the rotation promotes the establishment of a diversity of weed species and thus avoids flora specialization. A diverse flora is easier to manage.
"Economic" criteria
Long-term weed control cost: Decrease
The action plan should reduce the risk of infestation over time. Reduced risk implies lower weed control expenses. However, this decrease in weed control cost may be offset by additional costs for soil tillage or less profitable crops.
"Social" criteria
Peak period
Work distribution may change. For example, introducing spring crops implies more work in spring and less in autumn.
Observation time
Depends on the action plan implemented. Possible increase if rotation diversification.
Training needs: increase
Designing a new cropping system (and possibly introducing new crops in the rotation) requires acquiring new knowledge (weed biology, etc.)
For more information
- FlorSys: a model of the effect of cropping systems on weed demography
- -Gardarin A. (INRA): Munier-Jolain N. (INRA); Colbach N. (INRA) AFPP: twentieth COLUMA conference. International days on weed control, Dijon, December 11 and 12, 2007, Conference proceedings, 2007
- OdERA-Systems: a weed management tool
- -Munier-Jolain N. (INRA); Pernel J. (Agro-Transfert Ressources et Territoires) INRA, Agro-Transfert Ressources et Territoires, 2011 Conference article and poster
