Finding guidelines for vegetable-based intercropping design through a relay of meta-analyses. Framework and application to cabbages

Summary

Modern agriculture has been focused on improving and optimizing production, neglicting supporting and regulating ecosystem services. Meta-analysis has been a useful tool to demonstrate the potential of cereal-legume intercropping to deliver multiple ecosystem services and providing guidelines for their intercrop design. However, detailed guidelines for the design and management of such systems remain unclear, especially for the understudied vegetable-based intercropping systems. whether such premises apply to vegetable-based intercropping systems remains unknown. Given the diversity of vegetable crops, we propose a ‘relay’ of crop-specific meta-analyses to capitalize on vegetable intercropping research. Each ‘leg’ in the relay analyzes relevant performance criteria from the perspective of one focal crop, and over the course of subsequent legs the network of interactions among the different crops is built. We argue that this approach provides crop-specific guidelines and identify designing principles that are applicable under a range of different environmental conditions. We started the ‘relay’ meta-analysis focusing on cabbage (Brassica oleracea ssp.) and the delivery of the provisioning services productivity, product quality (grade and pest injury in cabbage products), and yield stability across different companion species, spatio-temporal configurations, and management inputs. We identified 72 studies across 62 field sites, comprising 564 data records. We show that intercropping did not significantly compromise cabbage productivity (-6 % on average) or grade (1%) and significantly reduced pest injury (53 %) relative to sole cabbage systems. Effects on yield stability remained unknown as trials were rarely conducted for more than two years, pointing to the need for long-term experimentation. Greater productivity was associated with short companion species with a low growing habit or types sown at or after planting of the cabbage crop thus limiting competition with cabbage at early development stages. The decrease in pest injuries was associated with intercropping patterns involving strong inter-plant interactions (i.e. mixed, row and additive) and companion species that supported biodiversity such as living mulches. Overall, beneficial effects of intercropping tended to be more evident in organic or no input production systems, possibly due to synthetic inputs overriding potential regulating effects and/or promote imbalance between the intercropped species. Cabbage growers and agricultural advisors can use these guidelines for designing intercrop systems specific to their local conditions. A more holistic understanding vegetable intercroping systems interactions can be achieved by implementing the database structure developed here with other crops and agro-ecosystem services