Sugarcane root biomass is a major component of carbon partitioning in plants and the carbon balance in cultivated soils. Each year sugarcane roots are decomposed , contributing to the pool of organic matter in the soil. Root biomass is especially important when the whole above - ground biomass is used for energy purposes (combustible, alcohol or other). The amounts of root biomass produced per unit area of cultivated soil are not well - known. The objective of the study was to quantify the biomass (above and below ground) production of some multipurpose cane varieties. Studies were conducted to investigate the agronomic effects of using the whole above - ground biomass of multipurpose sugarcane as an energy feedstock. A local conventional sugarcane variety (R579) and three multipurpose cane varieties (WI79460, WI81456, WI86015) were tested at the same location (South of Guadeloupe, on volcanic soils) and with the same cultural practices (planted cane , 1.6 m row spacing). Dry root biomass per unit volume (DRB) was measured from soil monoliths (3375 cm3 ) sampled at different depths (0-15, 15-30 and 30-45 cm) and different distances from the cane row (0-15, 18-33 and 53-68 cm) to account for gradients in RBD and to estimate below - ground biomass production. Fine (<1 mm) and thick roots (>1 mm) were measured separately because sugarcane specific root length are different (Chopart et al 2010). Thick and fine root turnover in soil may also be different. Conventional and multipurpose sugarcane varieties were mainly different in total shoot biomass. Total DRB values of sugar cane (R579) and multipurpose canes were 262 and 318 g/m² respectively. Vertical and horizontal gradients were high. DRB of thick roots were higher than DRB of fine roots. We compared root and total shoot dry biomass (sugarcane: 5400 g/m², multipurpose cane: 6600 g/m²). DRB of multipurpose sugarcane was lower than top biomass (860g/m²) but higher than dead fallen leaves (80 g/m²). DRB is an important