Screenhouse-based shade-tolerance assessments of coffee and bean varieties, and cover crops, to optimize multi-strata intercropping in African smallholder systems

Intercropping annuals with perennials like banana, coffee, and trees is common in East and Central Africa, where farms are small and fragmented, but shade often limits crop productivity. This study screened bean varieties, Arabica coffee, and cover crops under different light levels (70%, 50%, 35%, and 10% of full sunlight). Several bush and climbing bean varieties maintained yields under moderate shade, though only two bush beans (HM21-7 and CODMLB 499) performed well under very low light. Bush beans generally elongated in shade, while climbing beans varied in response. Coffee seedlings remained relatively stable across shade conditions, with only slight reductions in some varieties. In contrast, cover crops performed poorly, with major biomass losses—especially elephant grass, while velvet bean and rattle pod also declined significantly despite retaining some root mass. Overall, the results highlight substantial variation in shade tolerance among beans and coffee, suggesting that selecting tolerant varieties can improve productivity in shaded systems, whereas many common cover crops are unsuitable.