Organic farming and seminatural habitats for multifunctional agriculture: a case study in hedgerow landscapes of Brittany

Finding more sustainable ways to produce food is a major challenge for humanity in the face of biodiversity extinction and climate change. Consequently, research on the ability of agroecosystems to provide multiple functions is growing. In this regard, the relative importance of organic farming and landscape-scale measures for improving multifunctionality has recently been debated. We investigated the effects of the farming system (conventional vs organic) at the field scale, the total length of hedgerows in the landscape, and their interaction with the multifunctionality of 40 winter cereal fields in Brittany (France). Our multifunctionality assessment integrated 21 indicators of biodiversity conservation, nutrient cycling, soil structure, pest and disease regulation, food production, and socio-economic performance. Many indicators of biodiversity conservation, pest and disease regulation, and socio-economic performance were higher in organic than in conventional systems. However, indicators of nutrient cycling and soil structure did not improve and food production was much lower in organic systems. Total hedgerow length in the landscape had less influence than organic farming on indicators, although we observed positive interactions. Granivorous carabid abundance and semi-net margin were highest in organic fields located in well-preserved hedgerow landscapes. Our study suggests that field-scale organic farming is necessary to promote biodiversity conservation and associated ecological functioning in crop fields, whereas landscape-scale preservation of semi-natural habitats alone is likely insufficient. Preservation of hedgerows in the landscape brings additional ecological and socio-economic benefits for organic systems without compromising agricultural production. More broadly, our results call for more ambitious research into the myriad possible combinations of farming practices and agri-environmental measures at both field and landscape scales, to improve both belowground and aboveground functioning.

Methods
We conducted the study in the southern part of the Zone Atelier Armorique, a Long-Term Socio-Ecological Research (LTSER) site in Brittany, France (47°59′35 N, 1°45′12 W). This region is characterized by dense hedgerow networks and crop-livestock farming systems. We selected 40 cereal fields, half under long-term organic farming (generally >20 years) and half under conventional farming. Crop fields were located along a gradient of total hedgerow length in the landscape. Field sampling was performed between April and July 2019 in winter cereal fields. Samples were collected in crop fields at least 5 m away and up to 50 m from field margins. In the manuscript, we describe the protocols for the measurement of soil enzyme activities and physicochemical properties, sampling of soil microorganisms, earthworms, weeds, crop disease severity, aphids and mummies, and natural enemies.