A multidisciplinary on-farm survey of maize-bean intercropping highlights key considerations for reviving traditional agricultural systems.
Résumé
Cereal-legume intercropping is a promising strategy for sustainable agroecosystems. The traditional intercropping of maize and bean is experiencing a revival in some modern agricultural settings, such as in southwestern France, where maize hybrids are intercropped with the commercialized Tarbais bean. We conducted on-farm surveys to address the following questions: How do intercropping and sole cropping impact yield, nutrient uptake and rhizosphere bacterial assemblages? Do positive or negative interactions between maize and bean dominate in intercropping at the phenotypic level? What is the effect of intercropping at the transcriptomic level? We recorded technical itineraries, conducted yield and nutrient measurements, and characterized soil bacterial assemblages via metabarcoding to compare sole cropped maize and beans with intercropped plants. We also set up a controlled field assay to quantify differentially expressed (DE) genes between cropping systems. We observed an increase in bacterial diversity in intercropping and a significant impact of the cropping system on agronomic traits, with frequent farm-by-cropping system interactions. Competition dominated maize-bean intercropping, with 56 out of 90 significant negative correlations between maize and bean traits. The bean displayed lower yield in intercropping but greater seed size, weight, nitrogen and carbon percentages. From the controlled field assay, we found that competition primarily affected the beans and their transcriptome, with nearly 30% of DE genes detected while none were found in maize. Overall, our findings suggest that synergies between the two crops are likely hindered, underscoring the importance of carefully considering partner varieties and technical itineraries in the revival of traditional agricultural systems.
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