A 7-year multi-criteria analysis of sugarcane intercropping compared to conventional cropping systems

Abstract Long-term studies are crucial for evaluating how intercropping affects the agronomic, environmental, and socio-economic sustainability of sugarcane systems. Intercropping with cover crops is expected to improve soil fertility and reduce herbicide use; however, its long-term effects on yield, weed dynamics, and production costs remain unclear, particularly under tropical conditions. Weed pressure has been hypothesized to drive yield decline over time, yet the temporal evolution of weed communities and their consequences for system sustainability remain poorly understood. We hypothesized that intercropping would modify ecosystem functions and services by increasing weed diversity and soil fertility, reducing herbicide use, and also increasing labor and production costs. To test this hypothesis, we conducted the first 7-year field experiment on Reunion Island, comparing four sugarcane intercropping systems with conventional chemical and low weed control systems. A multi-criteria approach assessed weed community dynamics, soil fertility, sugarcane yield and quality, herbicide use, labor, and economic performance over a complete crop cycle, including multiple ratoons. We show that weed pressure increased over time in both chemical and intercropping systems due to greater weed cover and species richness. Weed community structure differed during the first 3 years but later homogenized under sugarcane dominance. This increase led to more manual weeding in intercropping systems and to increased herbicide use in chemical ones, resulting in a 61% reduction in herbicide use under intercropping. After 7 years, soil chemical and biological fertility remained unchanged, while physical fertility improved with companion crop and weed development. Sugarcane yield and sucrose content were maintained, but production costs and working hours increased. This study demonstrates that sugarcane intercropping reduces herbicide dependence without compromising yield, though at higher labor costs. Systems maintaining spontaneous flora in inter-rows appear to offer a promising compromise for sustainable weed management. Further research on this system should be conducted in different pedoclimatic conditions.