Associating Rapeseed with Frost-Sensitive Cover Crops

From Triple Performance
Technical articles
Crop association in arable farming Management of cover crops in arable farming Climate resilience Soil cover Biodiversity Soil regeneration Associated rapeseed


This technique consists of sowing, at the same time as winter rapeseed, frost-sensitive service plants that are not harvested (or companion plants) and intended to accompany winter rapeseed during autumn, during the first part of its vegetative cycle, in order to provide services to the winter rapeseed crop. The cover crop is destroyed during winter by frost and the rapeseed continues its cycle alone in spring.

Services sought

  • Improve nitrogen nutrition of rapeseed in autumn and then in spring: In autumn, association with frost-sensitive legumes increases the nitrogen nutrition index of rapeseed. In spring, after winter destruction by frost, the legumes return part of the nitrogen fixed in autumn to the rapeseed.
  • Limit damage caused by insects in autumn (larvae of flea beetles and terminal bud weevils) by direct effects of camouflage, visual and/or olfactory disruption, and indirect effects linked to improved nitrogen status of rapeseed and thus its growth dynamics.
  • Structure the soil and improve rapeseed rooting through complementarity of root systems (rapeseed/service plants).
  • Achieve better soil cover and limit the development of weeds (competition or allelopathy).
  • Contribute to improving soil fertility in the medium and long term. Service plants associated with rapeseed increase the total biomass produced on the plot. By decomposing, frost-sensitive legumes contribute to carbon and nitrogen storage (part of nitrogen not rapidly mineralized) in the soil. The various effects of service plants on rapeseed allow savings on inputs (nitrogen, herbicide, sometimes insecticide) and maintain (or increase) rapeseed yield.

This technique requires some adjustments to the technical itinerary but is easily accepted by farmers as it does not require major reorganization of the cropping system.

Conditions for success

It appears preferable to associate rapeseed with one or more frost-sensitive species exerting limited competition on rapeseed. Therefore, legumes (Fabaceae) should be favored, as they are less competitive for nitrogen and also provide the service of "nitrogen supply" through their ability to use atmospheric nitrogen (symbiotic fixation) for growth and are early (more sensitive to frost when developed). It is important to limit health risks by choosing species not present in the rotation or not multiplying pathogens of rotation species (notably the case of Aphanomyces which requires excluding lentils, vetch, and sensitive varieties of vetches and clovers in rotations including sensitive crops such as peas or lentils).

It is also possible to associate non-legumes (flax, buckwheat...) with rapeseed, with caution regarding risks of competition and counterproductive effects as with buckwheat. Another type of association can be with perennial legumes. However, the choice of perennial species should not start too early in spring, and associating frost-sensitive legumes will limit the development of weeds and promote rapeseed growth.

To promote both the development of service plants and rapeseed, early emergence must be achieved, which implies:

  • early sowing (generally in the first two decades of August, at the beginning of the recommended sowing date ranges by Terres Inovia)
  • optimizing soil work by avoiding drying out as much as possible.

Finally, weed control must be adapted because full-dose programs are not selective enough for most legumes.

Since 2010, the areas managed with "associated rapeseed with service plants" have been steadily increasing. Farmers are very satisfied and report no yield losses and much less insecticide use in autumn (2 to 4 fewer passes!). This momentum should be continued.

Details on the technique

Species choice

Varietal choice for rapeseed can be adapted, particularly regarding low sensitivity to autumn elongation. Examples of pure species are available on page 3 of the technical sheet "associating a cover with rapeseed" from the Meuse Chamber of Agriculture, or in mixtures in the publication "Associated rapeseed with a frost-sensitive legume cover" by Terres Inovia (pages 12 for mixtures of 2 or 3 legume species, pages 14 and 15 for mixtures evaluated and/or marketed in 2015), such as:

  • Lentil (30 Kg/ha)
  • Spring faba bean (80 Kg/ha). However, faba bean seeds, being quite large, sometimes complicate sowing.
  • Alexandrian clover (6 Kg/ha, e.g. variety Tabor)
  • Mixture of spring faba bean (50 Kg/ha) and lentil (15 Kg/ha)
  • Mixture of spring faba bean (50 Kg/ha), common vetch (10 Kg/ha, e.g. variety Nacre) and clover Alexandrian (5 Kg/ha, e.g. variety Tabor)
  • Commercial mixtures of common vetch, purple vetch and Alexandrian clover (Jouffray-Drillaud) or of vetch, fenugreek and lentil (Sem-partners) sown at 20-25 Kg/ha.

Establishment of service plants

Early sowing, between August 1 and August 20 depending on regions, is preferred to maximize temperature sum and growth of service plants. Service plants can be established:

  • Simultaneously with rapeseed on the same sowing line (cereal seeder).
  • Simultaneously with rapeseed alternating sowing lines (seeder with separate hoppers).
  • In two passes: the rapeseed sowing is done after the broadcast sowing of the cover. Rapeseed sowing density remains unchanged. Rolling then ensures good seed-soil contact. Particular attention should be paid to seed mixture homogeneity when species have different seed sizes (e.g., rapeseed + faba bean or rapeseed + clover).

Maintenance

If service plants emerge early and develop significantly, a 30-unit reduction in nitrogen fertilization can be made in spring for rapeseed.

Destruction

Service plants generally freeze during winter. Chemical weed control will be necessary if they have not frozen and risk hindering crop development at regrowth.

Testimonials

Here are some testimonials on associating rapeseed with service plants:

  • In organic farming, success factors according to Pascale Croc and Garry Charre (17):
  • Service plants, for rapeseed and beyond according to Christophe Bouyé (47):
  • With faba bean, easy organization and convincing results according to Gianny Bonnouvrier (17):

Some decision support tools

The Cover crop choice tools from Arvalis and ACACIA from GIEE Magellan provide assistance in cover crop choice to associate with rapeseed, considering expected benefits and risks at the rotation scale.

The Species choice support tool for rapeseed (CAPS) was developed by INRAE and partners of the Casdar ALLIANCE project to help choose cover crop species based on desired services.

Implementation period

At establishment: Service plants can be sown simultaneously with rapeseed. For large seeds like faba bean, if the seeder is not equipped with a double hopper, sowing with a fertilizer seeder is preferable before the seedbed preparation tool or with a cereal seeder before rapeseed sowing with a single seed drill.

Application of the technique

Neutre Generalizing this technique to all crops is sometimes challenging. Associations of service plants with other crops are under experimentation (association with wheat, lupin, corn, sunflower, etc).

Positif This technique is easily generalizable to all soil types. Establishing a legume cover crop alongside rapeseed can be applied to all soil types. This technique is particularly interesting in shallow soils, with low nitrogen availability, and/or in situations with high autumn insect pressure. Expected services are probably harder to achieve in situations with fewer limiting factors, in deep soils with high potential, and in regions where autumn insects are not problematic.

Neutre This technique will not be generalizable to all climatic contexts. In northern and eastern France, the climate may be unfavorable to the growth of service plants in autumn, with the risk that expected services are not effectively provided. Sowing in the first 15 days of August is preferable to benefit from still mild temperatures.

In regions with low frost occurrence (e.g., oceanic climate), the choice of service plants is limited to species capable of decomposing even without significant frost (single-cut Alexandrian clover, vetch, fenugreek). Chemical destruction may be necessary as a catch-up.

Regulations

The establishment of an association of frost-sensitive legumes or a cover of frost-sensitive and non-frost-sensitive legumes is subject to CEPP sheets (Phytopharmaceutical Product Savings Certificates):

  • Action No. 10: Replace autumn herbicide and insecticide treatments by associating frost-sensitive legumes with winter rapeseed.
  • Action No. 50: Reduce phytopharmaceutical product use by associating a cover of frost-sensitive and non-frost-sensitive legumes between rapeseed rows.

As of the article writing date (08/09/2021), it is possible to declare rapeseed as EFA (Ecological Focus Area) under the CAP.

Services provided by the technique

Weed regulation and management

Service plants compete with weeds for resources and suppress them. Note, this technique needs to be combined with other complementary techniques: lengthening rotations, possibly no-till to limit problematic dicotyledonous weed emergence such as geraniums, etc. Effect level: MEDIUM if used alone, to be combined.

Confidence level: MEDIUM.

Pest management

Legume-based service plants have a dual action limiting insect larval damage:

  • direct insect disturbance action resulting in reduced larvae per plant, provided companion plants develop sufficiently (>200g/m² entering winter)
  • indirect action improving rapeseed nitrogen nutrition, resulting in better growth dynamics and thus less sensitivity to larvae presence.

Effect level: MEDIUM if used alone, to be combined.

Confidence level: MEDIUM.

Nutrient supply

The technique promotes nitrogen nutrition of rapeseed in autumn and spring. If legumes have significant and early development, a 30-unit nitrogen reduction is recommended. Early observations suggest nitrogen nutrition benefits on the following wheat, but these remain to be quantified.

Effect level: MEDIUM if used alone, to be combined.

Confidence level: MEDIUM.

Physical stability and soil structuring

The multiple root systems in the association structure the soil and facilitate rapeseed rooting. Moreover, faba bean can help break a crust that would prevent rapeseed emergence.

Effect level: MEDIUM if used alone, to be combined.

Confidence level: MEDIUM.

Water storage and management

Root systems of companion plants improve water circulation in hydromorphic soils, especially verified with faba bean.

Effect level: MEDIUM if used alone, to be combined.

Confidence level: MEDIUM.

Effects on cropping system sustainability

Environmental criteria

Positif Effect on air quality: Increasing. Association of service plants with rapeseed reduces phytosanitary treatment use (herbicides, insecticides). If not destroyed by frost, chemical weed control may still be necessary after winter.

Positif Effect on water quality: Increasing. Association of service plants with winter rapeseed reduces the amount of phytosanitary treatments (herbicides, insecticides), thus reducing risks of transfer to groundwater variably depending on molecules. It also increases root exploration of the soil and nitrate uptake in autumn, limiting leaching risks. When using "legume" service plants, a 30-unit reduction of mineral nitrogen inputs on rapeseed can be considered. If service plants are not destroyed by frost, chemical weed control may still be necessary after winter.

Positif Effect on fossil resource consumption: Decreasing. Association of service plants with rapeseed reduces nitrogen input and number of phytosanitary treatment passes, thus:

  • Lower fossil energy consumption linked to mineral fertilizer production and tractor use,
  • Lower greenhouse gas emissions (CO2) linked to mineral fertilizer production and spreading and tractor use.

However, cover establishment may require an additional pass.

Agronomic criteria

Neutre Productivity: No effect (neutral). In most situations, the effect on rapeseed yield is neutral to positive (Alliance project). Positive yield effects are observed especially in successful establishment and good cover development situations, in shallower soils, and under high autumn insect pressure. Rare yield losses are linked to legumes that do not freeze and compete with rapeseed in autumn (cases of vetches, faba beans, and multi-cut Alexandrian clovers). These situations can be avoided by choosing species with good winter behavior (single-cut Alexandrian clover, vetch, fenugreek, lentil) and using chemical catch-up as a last resort.

Neutre Production quality: No effect (neutral).

Positif Soil fertility: Increasing. Establishing a legume cover improves nitrogen availability for rapeseed (symbiotic fixation, better root exploration, and nitrogen return from decomposed service plant residues). Some experiments and farmer observations report additional nitrogen for the following crop after associated rapeseed, or with white clover maintained throughout the rapeseed cycle and destroyed before the following wheat. Finally, the additional biomass produced by the association compared to rapeseed alone contributes to increased C and N storage in soil (see results of the SOLEBIOM project).

Neutre Water stress: Variable. In case of low autumn rainfall and very competitive cover, early cycle water stress risks for rapeseed may increase but are mostly not impactful on final rapeseed development. Rapeseed can "catch up" in spring for biomass deficits observed in autumn (cf. Casdar Alliance project).

Positif Functional biodiversity: Increasing. Some service plant species can attract flying beneficial insects by providing resources (early flowering of buckwheat, extrafloral nectar secretion by faba bean). Increased soil cover may favor soil predators by providing a favorable habitat.

Neutre Disease risk: Variable. Aphanomyces: In rotations including a sensitive species such as peas or lentil as a cash crop, avoid species and varieties that multiply the pathogen (cases of peas, lentils, vetches, some clover and vetch varieties). Favor faba bean, Alexandrian clover, and non-sensitive vetch varieties that do not multiply the pathogen (list of sensitive species and varieties).

In general, do not use as service plants species already grown as cash crops in the rotation.

Economic criteria

Neutre Operating costs: Variable. The association of service plants with oilseed rape involves additional costs of €30 to €80/ha for seeds. However, this technique should lead to a reduction in phytosanitary treatments and fertilizers, with operating costs not very different from oilseed rape grown in pure culture.

Neutre Mechanization costs: Variable. The association of service plants with oilseed rape may involve an additional pass at sowing but may avoid other passes related to the reduced use of pesticides and nitrogen, with mechanization costs not very different from oilseed rape grown in pure culture.

Positif Margin: Increasing. In a network of 10 trials (Casdar Alliance project 2014-2017), average increase in semi-net margin of +€32/ha in cases of significant reductions in the use of inputs. The additional cost of establishing the cover crop (seeds + sowing) is offset by the reduction of input costs and associated passes. The impact on the margin therefore depends on the effective reduction in input use, as well as the effect of the cover crop on yield.

Neutre Fuel consumption: Variable. The association of service plants with oilseed rape may involve an additional pass at sowing but may avoid a pass for herbicide and insecticide application. These two items generally offset each other, with no overall effect on fuel consumption at the crop scale.

Social criteria

Neutre Working time: Variable. The association of service plants with oilseed rape may involve an additional pass at sowing but may avoid a pass for herbicide and insecticide application during periods of high workload (soil preparation and sowing of winter crops). The association of service plants with oilseed rape is an innovative practice requiring learning and observation.

Positif Peak period: Decreasing. The technique avoids a pass for herbicide and insecticide application during periods of high workload (soil preparation and sowing of winter crops).

Positif Effect on farmer health: Increasing. If reduction in exposure to phytosanitary products (insecticides, herbicides).

Favored or disadvantaged organisms

Bioagressors disadvantaged

Organism Impact of the technique Type Details
Flea beetle MEDIUM Pest, predator or parasite Companion plants that disturb insects and promote oilseed rape growth, resulting in reduced larval damage
Oilseed rape flea beetle MEDIUM Pest, predator or parasite
Terminal bud weevil MEDIUM Pest, predator or parasite Companion plants that disturb insects and promote oilseed rape growth, resulting in reduced larval damage
Noctuids LOW Pest, predator or parasite
Small flea beetle MEDIUM Pest, predator or parasite
Weeds MEDIUM Weeds

Auxiliaries favored

Organism Impact of the technique Type Details
Predatory and granivorous ground beetles LOW Natural enemies of bioagressors Legumes favor them thanks to a layered vegetation height
Diaeretiella rapae MEDIUM Natural enemies of bioagressors Parasitoid of grey aphids, favored by the presence of faba bean

For more information

Valantin-Morison M., Verret V., Médiène S., Gardarin A., Lorin M., Pelzer E., Celette F., Naudin C. Website, 2014

Trotin V. Chamber of Agriculture of Poitou Charentes, 2013

Cadoux S., Sauzet G., Valantin-Morison M., Pontet C., Champolivier L., Robert C., Lieven J., Flénet F., Mangenot O., Fauvin P., Landé N. Terres Inovia, Technical brochure, 2016

Cadoux S., Sauzet G., Valantin-Morison M., Pontet C., Champolivier L., Robert C., Lieven J., Flénet F., Mangenot O., Fauvin P., Landé N. OCL, Peer-reviewed journal article, 2015

Verret V., Gardarin A., Makowski D., Lorin M., Cadoux S., Butier A., Valantin-Morison M. Elsevier, Peer-reviewed journal article, 2017

Pillier A., Remy L., Robin P., Ronget D., Sauvdet F. Chamber of Agriculture of Côte-d'Or, Technical brochure, 2010

Archambaud M., Sauzet G. TCS, Press article, 2009

Thomas F. Excerpt from the film Secrets of the Fields by Honorine Perino, Rés'OGM Info / ADDOCS, Multimedia, 2012

Minette S., Trotin V., Ginestière Y. Regional Chamber of Agriculture New Aquitaine, Technical brochure, 2012

Jouffray-Drillaud, Technical brochure, 2014

Lorin M. Thesis defense, Academic work, 2016

Keywords

  • Bioagressor control method: Cultural control.
  • Mode of action: Mitigation, barrier.
  • Type of strategy regarding pesticide use: Substitution, redesign.

Related articles

Appendices

S'applique aux cultures suivantes

Défavorise les bioagresseurs suivants

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