Evidence map of crop diversification strategies at the global scale

The diversification of cropping systems encompasses different strategies that may help maintain orenhance the sustainability of agriculture. Thousands of experiments have been carried out around theworld since almostfive decades to evaluate and compare the performances of various diversificationstrategies in a wide array of agroecosystems and climates. Although these analyses have beensynthesized in a growing number of meta-analyses, the information remains somewhat fragmented. Amulticriteria systematic synthesis of worldwide agricultural diversification is still lacking. Here, wereview all meta-analyses conducted on crop diversification strategies and produce a detailed overviewof their results and of their quality. We identified and analyzed 99 meta-analyses summarizing theresults of more than 3700 agronomic experiments on seven crop diversification strategies. Amongthese strategies, rotation and associated plant species are dominant in the literature followed byintercropping, agroforestry and landscape heterogeneity. Our analysis reveals that rotation andintercropping are associated with yield increases. Agroforestry systematically induces an improvementof biodiversity and soil quality—in particular soil organic carbon. We show that, regardless of thecontext, a combination of several diversification strategies outperforms any individual strategy. Ourreview reveals that a significant knowledge gap remains, in particular regarding water use, farmers’profitability, product quality and production stability. Few meta-analyses investigate the performanceof landscape heterogeneity and of systems with species other than cereals and pulses. Additionally, weshow that most of the meta-analyses studied cannot be considered fully transparent and reproducible.Their conclusions should therefore be interpreted with caution. Our systematic mapping provides abenchmark to guide and improve the relevance and reliability of future meta-analyses in agronomy