CASTOR project, cover crops

The CASTOR project aims to study how plant cover can be combined with cereal crops to reduce input requirements (fertilizers and pesticides in particular) and propose more sustainable agricultural production practices. The aim of the CASTOR research programme is to conceive strategies for inserting multiservice leguminous cover crops in association with cash crops. The project also aims to work in synergy with all concerned stakeholders.

Keywords: Associated cover crops, Crop diversification, Cropping association, Innovative cropping techniques, Intercropping, Legumes, Multi-services cover crops, Regulation, Weeds

Funders: TERRA Isara, Compagnie National du Rhône (CNR)

Trèfle comme couvert végétal dans le projet CASTOR

Red and white clover flowers. M. Rouge, May 2022.

Clover cover associated with cereal. M. Rouge, June 2022.

Clover cover associated with cereals after harvest. M. Rouge, June 2022.

Relay intercropped clover sowing in cereals. M. Rouge, February 2022.

Clover cover crop. M. Rouge, February 2022.

Clover associated with cereals. M. Rouge, April 2022.

Clover associated with cereals at flowering stage. ISARA, May 2009.

Our experimental approach

The project is organised in three main steps:

Innovation tracking: The aim of the tracking phase was to identify and analyze experts (innovative farmers, advisors) implementing innovative techniques. This was achieved through a survey targeting farmers throughout France.
State of the art of the scientific literature: results were compared to the latest scientific knowledge on these techniques to identify any gaps between scientific work and the references needs of farmers and advisors, and to determine relevant research area.
Experimental part with partner/farmers: Setting up of an experimental plots network of 20 plots during two years to produce recommendation and address the barriers identified in the innovation tracking. On each experimental plot, forage legumes were sown as a relay cover crop in winter cereal with three different legume species and three sowing methods. All plots were monitored during the first year of association and half of them for two years (first year of association and the following crop) to assess the behavior of the cover crops in relation to various planting and management methods, and the level of ecosystem services obtained.

Main results

The results of the project are presented in the project summary, which is divided into three parts:

The first part presents the project, some results about the farmer survey carried out at the start of the project, and the scope and details of the experimental schemes involving clover as relay intercropping with straw cereal.
A second part deals with the results of the experimental network in farmers’ plots on the association phase between clovers and the straw cereal. This second part supports the results on the different technical practices (sowing methods and clover species) used in the plots and their impact on the success of the cover crop and cereal.
The final part of the research project summary looks at the evaluation of the services provided by the cover crops after the winter cereal harvest, during the intercropping period and during the following spring crop. The issues raised concern competition with weeds, nitrogen restitution for the following crop and soil structure in the presence of cover crops.

(The project summary is only available in French)

The project provided also answers to the following questions:

How cover crop planting strategies can be improved to maximize their chances of success of cover establishment?

Farmers whose cover crops fail to establish on fields don’t seem to take as much care in establishing them as they would do for the cash crop. Many farmers fear competition between the cover crop and the cash crop (which is generally non-existent or not strong, as the literature shows). Farmers surveyed during the innovation tracking study generally stressed the importance of careful cover crop establishment. The experiments carried out shows that the development of cover crop could be improved through planting techniques adapted to soil and climate conditions (e.g. sowing the cover crop in rows or with a direct seed drill; sowing a mixture to adapt to heterogeneous conditions).

Climatic trends in recent years mean that spring sowing is no longer a guarantee of favorable conditions for cover crop development. As a result, farmers need to think about adaptive strategies – for example, sowing earlier if conditions are favorable, or sowing in autumn, giving themselves the possibility of resowing several times during the year if the first sowing failed.

How cover crops should be managed to maximize expected services, particularly weed control?

During the innovation tracking part, some farmers stated that cover crops were unable to compete effectively with weeds. The experiments carried out showed a good link between cover crop biomass and weed control, with a biomass threshold around 2TMS/ha in September. In other cases, shredding is often necessary to prevent summer weeds from going to seed and give the advantage back to the clover cover crop.

Sowing a clover cover as a relay crop: what to expect from nitrogen restitution?

The nitrogen restitution of the cover crop seems to be higher than often estimated by farmers and advisors. Thus, despite biomass production often limited by climatic conditions during the two years of experimentation, the nitrogen present in the cover crop was returned significantly and rapidly to the following spring crop. The quantities of nitrogen returned by the cover crops during the early stages of the following spring crop were on average around 80kgN/ha for a cover crop of 2TMS/ha. A fairly linear relationship between the nitrogen present in the soil under the spring crop and the biomass of the cover crop was demonstrated.

What is the impact of cover crop on the associated cash crop?

The presence of an associated cover crop had no effect, either positive or negative, on the yield of the associated cereal. In the network of experimental plots, there was no difference observed between the various methods tested (sowing methods and clover species) and the control without cover. Nevertheless, sowing clover in rows showed an average yield slightly lower than other sowing methods, this result is not significant, but underlines the importance of good soil bearing conditions when using a drill at the end of winter.

Project team

Florian Celette, Edouard Sory, Camille Pierre, Mathieu Rouge, Thomas Lhuillery, Anthony Roume, Adeline Cadiergues, Vincent Tolon, Léo Fisselier et Lisa Ravel

Partners

INRAE (UMR Agronomy and SAS), Oxyane, Cérience, Haute Loire Bio and all the farmers who who took part in the trials, with our sincere thanks!

Publications (in French)

Présentation du projet des dispositifs

Améliorer la conduite des couverts en relais et leur réussite

Évaluer les services écosystémiques fournis par les couverts de trèfle en relais

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CASTOR – Cover crops to foster agroecological transition and input reduction

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Our experimental approach

Main results

Project team

Partners

Publications (in French)