How to integrate cover crops to enhance sustainability in banana and citrus cropping systems

In Martinique (French West Indies), because of the susceptibility of the insular environment, the demand from society and policy-makers is high for sustainable and environmentally friendly fruit production systems. In tropical wet areas, weed management is crucial but difficult to control without herbicides. Herbicide becomes the most important pesticide input in banana plantations and orchards, thus developing herbicide-free alternatives are a priority. Cover crop intercropping constitutes the best option. Besides weed control, we considered their ability to reduce runoff and soil erosion, to compete with the main crop for water and nutrients, to host pests and natural enemies, and to preserve biodiversity. Thus, cover crops turn into global services crops. A multi-step and multi-criteria grid was built to select the ideal cover crop. We tested it on banana fields and citrus orchards. First, cover crop pre-selection was common and checked for climate suitability, seed availability, height, status of noninvasive species and capacity to be perennial. Second, we assessed the agronomic behaviour of seven pre-selected cover crops under field conditions. We measured cover crop specific traits (germination rate, covering rate, perenniality, biomass production, root depth, nutrient uptake or recycling, regrowth after mowing, adaptation to shade). Last, according to each cropping system specifications, we designed prototypes with the most relevant cover crops. In citrus orchards, grasses characterized by a high covering index associated with a low biomass production were selected, but natural enemies hosting services were poor. In banana fields, grasses were intercropped too, but nitrogen competi¬tion, was too high and led to loss in banana yield. As a conclusion, we showed that the concept of an ideal cover plant has to be implemented and combined in a more efficient mixed cover system (grasses mixed with nitrogen fixing plants). (Résumé d'auteur