Designing wheat varietal mixtures in organic agriculture

Project title and acronym: Co-design of varietal associations for organic agriculture - CASABIO

Funded in the framework of the Call for projects "Innovation" 2017, the CASABIO project took place over 3 years (2017-2019).

Leaders: Jérôme Enjalbert (GQE - Le Moulon) and Arnaud Gauffreteau (Agronomy)

Non-academic partners: GAB IdF (Group for Organic Agriculture in Ile de France) and ITAB (Technical Institute for Organic Agriculture and Food)

Adapting the variety to the growing conditions is a major lever to increase production in quantity and quality. This varietal lever is all the more important as the control of the growing environment by chemical inputs is limited, and therefore particularly strategic in organic farming (AB). However, the diversification of cultural practices, production objectives and the increase in inter-annual variability of crop conditions makes this choice difficult and sometimes impossible. Mixing several varieties in a plot at the time of sowing offers the farmer the possibility to cumulate characteristics of interest at the plot level and to increase the stability of his production in the face of an uncertain climatic and sanitary context by not putting all his eggs in the same basket. This practice has increased significantly in recent years (representing less than 3% of soft wheat acreage in 2015, it now occupies 12%).

Figure 1: Evolution of the area of mixed varieties in France

Faced with this growing practice, farmers and advisors lack rules of association to choose among the many varieties available those that will form a successful mixture, taking into account the methods of conducting these mixtures.
New fundamental and practical knowledge on plant-plant interactions in mixtures must be mobilized to better valorize these mixtures. The objective of CASABio was therefore to develop rules for the association of wheat varieties, focusing on nitrogen nutrition and weed control, two major constraints for AB production systems.

The 3-year project was built for and with organic farmers in Ile de France who participated in the design of association rules, in the choice of mixtures to be tested and in their experimentation on their farms.

A first result of CASABIO, following co-design workshops with farmers, agricultural advisors and scientists, was the development of heuristic (mental) maps. These maps list throughout the crop cycle the diversity of cultural practices and varietal characteristics related to each practice, which allow to control weeds and to favor nitrogen nutrition of wheat in organic agriculture.

Fig 2: Workshops to identify cultural practices and varietal levers to control weeds and nitrogen nutrition.

Following these workshops, various mixture assembly rules developed previously (Wheatamix Project) were reworked in CASABIO, notably by developing a simplified model of competition for light between varieties. Some of the rules developed (notably on disease resistance) have been integrated into a Multicriteria Evaluation Tool, OPTIMIX, which is available online. This tool was also the subject of a workshop with farmers and advisors.

Figure 3: Optimix, an online tool for evaluating on several criteria the qualities of a varietal mixture proposed by the user 

Finally, the rules produced were used to select variety mixtures that were evaluated in a network of AB experiments and by their implementation by GAB-IdF farmers in on-farm trials. These trials allowed to observe very contrasted production situations in organic farming (low to high productivity). The mixtures did not show a clear effect on weeds compared to pure varieties. On the other hand, nitrogen valorization and especially bread-making quality benefited from a positive mixture effect.

This work, original in its motivation and partnership, is currently being pursued in the CASDAR SSV STABLE and ANR PPR-CPA MoBiDiv projects.

The project leader explains the project and its RESULTS in VIDEO (LabEx BASC scientific days, February 2021)