Wheat cultivar mixtures enhance the delivery of agroecosystem services compared to monocultures under contrasted tillage intensities and fertilization

Wheat cultivar mixtures provide a more complex and functional cropping system than monocultures. Their functionality may result in the delivery of agroecosystem services. However, research on cultivar mixture performance has mainly been done in controlled environments. Greenhouses and laboratory experiments do not account for environmental or agronomic factors that may influence the polyculture’s functionality. To fill this research gap, we set up a novel strip-split-block experimental design with three factors (wheat treatment, tillage, and fertilization) in a field long-term trial. We assessed the performance of the modern wheat cultivar Florence-Aurora and the traditional cultivars Xeixa (Triticum aestivum L. subsp. aestivum) and Forment (Triticum turgidum L. subsp. durum) monocultures and their mixture in providing aphid and weed control and promoting crop yield under contrasting tillage practices (moldboard ploughing vs. chisel ploughing) and fertilization (farmyard manure applied or not applied). We analyzed aphid abundance, number of aphids per tiller, parasitism rate, weed abundance and richness, and crop yield. Additionally, we examined wheat establishment, cover, phenology, and height for cultivar characterization. We observed that soil management practices affected some aspects of the cropping system. The wheat cultivars differed in their aphid susceptibility and weed suppression ability, with Florence-Aurora being less suppressant to weeds and more prone to aphid infestation. Most remarkably, our study shows for the first time that mixing wheat cultivars with distinguished traits enhances associational resistance for aphid and weed control. These benefits were specifically important under high weed infestations generated by reduced tillage. Moreover, the yield of Florence-Aurora monoculture and the mixture was found to be influenced by tillage and fertilization. Our study underscores how soil management practices impact the functionality of cultivar mixtures. This emphasizes the need for further field research to better understand the complexity of farming conditions that influence the delivery of agroecosystem services by cultivar mixtures.