Sugarcane is a semi-perennial crop cultivated on 22,700 ha in Reunion Island. It is still very dependent on phytosanitary products such as urea or herbicides. Within the framework of the ECOPHYTO plan and the reduction of herbicides, the reduction of chemicals inputs in sugarcane production is a major lever for reducing the herbicide treatment frequency index (HTFI). One solution is the introduction of leguminous as companion crop in sugarcane crops to control weeds and fix atmospheric nitrogen. However, few studies have been focused on the underlying processes of competition between species, in particular the root compartment, which will be a determining factor in the distribution of resources. We therefore proposed to study the root response of sugarcane in association with companion crops under contrasting nitrogen and water availability. We observed that the presence of companion crops impacts the root biomass density in the cane row rather than in the interrow. Root density decreased with depth and with increasing distance from the cane row, whether in pure or in association. In general, 80% of the roots were found in the first 30 cm and more than 50% of the roots were found as close as possible to the cane row, whether in association or pure. Finally, the root density of the cane is affected by the availability of nitrogen and water. It was possible to observe an increase in root density for the irrigated treatments: 47% for the irrigated, unfertilised treatment and 27% for the irrigated, fertilised treatment. The opposite trend was observed for the roots of the companion crop with +18% root density for the non-irrigated and +51% root density for the fertilized modalities. In view of the preliminary results, there did not seem to be any separation of root niches between the companion crop and the sugarcane but a competitive impact on cane growth.