Relay intercropping a winter cereal with a legume sown in spring
This technique aims to establish, from spring onwards, a cover crop sown mainly broadcast in a winter or spring wheat crop. The objective is to promote the establishment of the cover crop at a time when conditions are more favorable than at harvest sowing and thus increase the biomass produced and soil protection from the cereal harvest.
Authors: Valentin Verret (INRA), Florian Celette (ISARA-Lyon) and Sébastien Minette (Regional Chamber of Agriculture of New Aquitaine).
Presentation
Characterization of the technique
Description of the technique:
The associated species most often belong to the family of perennial forage legumes: white clover, red clover, alfalfa, minette, etc. In 2017, this practice remains mainly used in organic farming.
The legume is generally sown broadcast, at the stem elongation stage of wheat, during the last pass of mechanical weeding (hoe, harrow) to promote seed-soil contact. Relay sowing in spring allows to limit competition between the cover crop and the wheat crop during the association phase to ensure the performance of the cash crop (yield and protein content).
From the wheat harvest, competition for light is lifted, allowing the cover crop to develop and utilize summer radiation to produce plant biomass expected to provide multiple services: weed regulation, nitrogen fixation for return to the following crop (enriching the soil-plant system), soil structuring and other agronomic effects of cover crops established more conventionally. In the following winter or spring, the forage legume can be harvested or plowed under (before a spring crop, do not destroy the cover before December to avoid early nitrate leaching risk).
Examples of species relay-sown in winter wheat
- Red clover (20 kg/ha)
- White clover (6 kg/ha)
- Minette (25 kg/ha)
- Alfalfa (25 kg/ha)
Details on the technique:
In organic farming, the technique is simple to implement, easily accepted by farmers as it does not require major reorganization of the cropping system. It offers clear advantages for nitrogen supply and weed management during the following intercrop (a good cover crop maintains a satisfactory weed status but does not allow a "cleaning of the plot"). For livestock farmers, it enables the production of supplementary forage in autumn.
In conventional farming, implementation problems may arise requiring adaptation of technical itineraries:
- Wheat cover too dense, not letting light through: too strong competition with the cover crop at its establishment.
- Suspected residual phytotoxicity on legumes caused by herbicides used on wheat or previous crop (sulfonylurea, etc.)
- Early ammonium nitrate application on wheat inhibits legume development and increases wheat competitiveness.
- Mechanical weeding equipment not always available on conventional farms (harrow, etc.)
- Cover crop/crop competition possibly leading to yield reduction on the wheat crop
Thus, there are several causes that can explain failures in legume establishment in conventional systems.
Favorable situations for legume establishment:
- Wheat crop that still lets radiation through in spring: low seeding density, low tillering variety, practice of mechanical weeding in early spring.
- Non-limiting water situation in spring (caution on shallow soils).
Application of the technique to...
Implementation period During the intercrop, on established cropSpatial scale of implementation Plot
All crops: Easily generalizable to all cereals with straw.
Associations of legumes with winter wheat at other periods are under experimentation: sowing the legume at the same time as wheat in autumn, sowing wheat in a permanent cover (e.g. alfalfa or white clover).
All soil types: Generalization sometimes delicate, it can apply to many soil types. However, caution in drying soil situations where water may limit legume establishment.
Therefore, species (and variety) choice must be adapted to soil characteristics (e.g. alfalfa dislikes acidic soils, pH < 6).
All climatic contexts: Generalization sometimes delicate
Adapted to Continental, Oceanic and Mediterranean climates. Practice studied in the Auvergne-Rhône-Alpes region since 2011.
Beware of situations with high risk of water stress, low spring precipitation. Subsequently, biomass production during the intercrop may be limited under dry conditions. Also adapt species (and variety) choice to the climatic context.
Regulations
Caution in water-sensitive zones, where intercrop covers composed solely of legumes are prohibited. In these situations, overseeding of another non-legume species at cereal harvest may be considered. Also, do not destroy the cover before December to avoid rapid nitrate leaching risk.
Effects on cropping system sustainability
"Environmental" criteria
Effect on air quality: Variable
Acidification : UNKNOWN
Pesticide emissions : VARIABLE
GHG emissions: UNKNOWN
Particulate emissions : NEUTRAL
If this practice reduces the use of pesticide treatments, transfers to air by volatilization of active substances will also be limited. It remains to verify in practices if cover crop effects reduce treatment use (cases studied are mainly in organic farming).
Moreover, this technique also allows some reduction of greenhouse gas emissions (details below), but a caution remains: GHG emissions linked to degradation of crop legume residues (N2O for example) are still poorly estimated.
Effect on water quality: Variable
Eutrophication : VARIABLE
Pesticides : VARIABLE
Turbidity : NEUTRAL
The association of a relay legume in wheat helps limit nutrient losses in winter by their immobilization in legume biomass during autumn. However, early destruction of the cover in autumn increases leaching risks during winter. This practice secures intercrop cover establishment compared to sowing at wheat harvest. With a better cover, leaching losses are better controlled. Nutrient recycling by return to the next crop allows fertilizer savings and potentially reduces pollutant transfers linked to overdosing.
Effect on fossil resource consumption: Decreasing
Fossil energy consumption : DECREASE
Phosphorus consumption : UNKNOWN
Pooling the sowing operation of the cover crop with mechanical weeding in spring avoids an additional pass for cover sowing in summer, thus saving fuel consumption related to tractor use. Possible nitrogen fertilizer savings on the following crop reduce fossil energy consumption linked to fertilizer manufacture and transport.
"Agronomic" criteria
Productivity: No effect (neutral), the staggered sowing date between legume and wheat limits competition effects exerted by the legume on wheat.
With secured cover establishment, overall system biomass production is increased, and beneficial effects of "green manure" covers can alleviate some factors limiting system productivity (competition from weeds, nitrogen-limited nutrition).
Production quality: Variable
In organic farming, excessive legume development does not impact wheat yield but may cause a noticeable decrease in protein content on wheat, for species best tolerating wheat competition (alfalfa, minette)[1].
Soil fertility: Increasing, establishing a legume cover increases the nitrogen stock of the soil-plant system at the cropping system scale. The "green manure" effects of the cover contribute to soil protection, structuring, etc., thus preserving soil fertility.
Water stress: Variable, in dry springs and drying soil, despite its advanced development, wheat may suffer competition from the cover for water if the associated species establishes well and grows vigorously. A well-developed cover will deplete available soil water stock, possibly affecting protein content or cereal yield.
Being in establishment phase, the cover will be sensitive to competition exerted by wheat for water in spring.
Functional Biodiversity: No knowledge on impact, diversification and soil cover after wheat harvest could have a positive effect on development of natural enemies of crops and functional biodiversity.
Other agronomic criteria: Variable
On diseases, the cover association could have effects:
- sometimes positive: reduced "disease" risk due to crop diversification "associated plant effect".
- sometimes negative: possible development of certain diseases (e.g. aphanomyces, sclerotinia) with service plants "legumes" that may host these diseases
"Economic" criteria
Operational costs: Variable, investment linked to legume seed purchase must be largely offset by nitrogen savings on the following crop. A higher investment would have been made anyway in the case of a long intercrop, with purchase of other cover crop seeds probably more expensive than clover seeds for example.
Mechanization costs: No effect (neutral), sowing operation has no extra cost if combined with mechanical weeding. Cover destruction operation is not strictly linked to this practice but to any soil cover practice during intercrop.
Margin: Variable
Slight increase in costs on the current crop with purchase of legume seeds.
Margin decrease if impact on yield or grain quality (protein content).
Fertilizer cost reduction on the following crop.
"Social" criteria
Working time: No effect (neutral), no effect if operation combined with mechanical weeding (except preparation time of sowing equipment).
Peak period: Decreasing, sowing the intercrop cover in spring rather than summer during harvest.
Observation time: Increasing, this practice is innovative requiring learning and observations.
Favored or disadvantaged organisms
Favored bioagressors
| Organism | Technique impact | Type | Details |
|---|---|---|---|
| aphanomyces | pathogen (bioagressor) | Caution to choose species little sensitive and non-hosts of diseases affecting other crops in rotation: e.g. aphanomyces if pea in rotation... | |
| slug | pest, predator or parasite | Effect of the presence of a cover crop in late winter. No measures to confirm / suspicion and possible negative effect on cover establishment | |
| sclerotinia | pathogen (bioagressor) | Caution to choose species little sensitive and non-hosts of diseases affecting other crops in rotation: e.g. sclerotinia if oilseed rape in rotation |
Disfavored bioagressors
| Organism | Technique impact | Type | Details |
|---|---|---|---|
| weeds | MEDIUM | weeds | Suppression of weeds likely to develop in the system during intercrop (medium efficacy if technique used alone, to be combined) |
Natural enemies favored
| Organism | Technique impact | Type | Details |
|---|---|---|---|
| Ground beetles predatory and granivorous | LOW | Natural enemies of bioagressors | Presence of a vegetative cover favors populations of walking insects |
| Pollinators | MEDIUM | Pollinators | Provided the cover flowers before destruction |
5. For further information
- Experimental analysis of the effect of relay legume covers associated with winter wheat, conducted in organic farming, on crop performance, weed control and nitrogen dynamics - Camille Amossé (ISARA-Lyon), university work, 2013. Link to thesis references
- Association of a cash crop and companion species providing ecosystem services
- -Muriel Valantin-Morison (INRA), Christophe David (ISARA), Stéphane Cadoux (Terres Innovia), Mathieu Lorin (INRA), Florian Celette (ISARA), Camille Amossé (ISARA), Annick Basset (Jouffray-Drillaud), Innovations Agronomiques 40 (2014), 93-112 (Carrefours de l’innovation agronomique, November 2014, ESA d’Angers), Non-peer-reviewed journal article, 201. Link to article. Link to presentation. Link to presentation video
- Association of a service forage legume with winter soft wheat in organic farming: explanatory factors of variability of ecological services provided by the legume and ways to optimize the trade-off between services provided by the association - Sylvain Vrignon-Brenas (ISARA-Lyon), Thesis, University work, 2016
- Relay association wheat / forage legume in organic cereal system: a response for weed control and nitrogen nutrition of crops - C. Amossé (ISARA-Lyon) F. Celette (ISARA-Lyon) MH. Jeuffroy (INRA) C. David (ISARA-Lyon) Innovations Agronomiques 32 (2013),21-33, Non-peer-reviewed journal article, 2013. Link to article
- Relay sowing cereals and forage legumes - C. Amossé (ISARA-Lyon) F. Celette (ISARA-Lyon) C. David (ISARA-Lyon) AlterAgri, May-June 2013, p14-16, Non-peer-reviewed journal article, 2013. Link to article
- CASDAR Alliance Project - Coord. Muriel Valantin-Morison (INRA), Casdar Research & Innovation, Professional report, 2017 Link to project webpage
Appendices
Est complémentaire des leviers
S'applique aux cultures suivantes
Favorise les bioagresseurs suivants
Favorise les auxiliaires
Défavorise les bioagresseurs suivants
La version initiale de cet article a été rédigée par Valentin Verret, Florian Celette et Sébastien Minette.
- ↑ C. Amossé, AgroParisTech, Experimental analysis of the effect of relay legume covers associated with winter wheat, conducted in organic farming, on crop performance, weed control and nitrogen dynamics, 2013. http://www.theses.fr/2013AGPT0009
