Conservation agriculture : how farmers manage weeds

International audienceConservation agriculture is characterized by the continuousand simultaneous application of three principles:minimum soil disturbance (no-tillage), residue cover onthe soil surface (dead mulch or cover crop) and diversecrop successions and cover crop mixes. Adopted inFrance by farmers since the 1990s, this farming systemstill faces some challenges to its adoption, particularlyfor weed management. To highlight this problem,425 French farmers practicing conservation agriculturewere surveyed by an online survey. Cultural practicesused to manage weeds during the first years of conservationagriculture were requested. The use of each culturalpractices was first studied independently. Then, amultiple correspondence analysis followed by a hierarchicalascendant classification resulted in groups offarmers with different combinations of practices.During first years of conservation agriculture, chemicalweeding during the crop cycle was divided between apost-emergence application only (49%), a pre-emergenceapplication only (13%) or the use of both applications(38%). Spot management on weed patches(51%) and on field border (30%) was also part ofweed management. Cover crops and intercroppingperiod weeding represented the main points of weedmanagement for 80% of the farmers. Another practiceto compete weeds by adding such as cover cropswas the use of combined/companion crops by 37% offarmers. To manage weeds, many farmers also usedpractices to avoid emergence of weed cohorts, suchas sowing date optimization (39%), crop rotation optimization(48%) and alternating sowing periods (61%).Increasing crop competitiveness was not part of theweed management strategy. Only 8% of farmers optimizedrow widths and used a variety to compete withweeds. Seeding rate optimization was used by 24% ofthe farmers . When regarding to the combinationsof these cropping practices, six groups of farmers wereidentified. Main contributing practices for partitioningthe groups were chemical weeding (crop weeding andintercropping period weeding), increasing competitionby adding species (cover crops, combined/companioncrops) and crop competition (sowing rate optimization).Thanks to the active participation of farmers’ networksduring the broadcast, the use of an online survey resultedin effective responses to our questions