The objective of this work was to evaluate a method to determine sugarcane roots with active metabolism and its distribution and growth in the soil profile, by using isotopic dilution technique with 15N. The experimental design was in randomized blocks, the split plot was considered in relation to time. The 15N tracer was applied in the leaves of the plants as urea solution. After the harvest of the above ground part of sugarcane plants, trenches were opened and the soil + roots samples were taken by monolite. The isotopic dilution method with 15N allowed evaluating active root mass and the root distribution in the soil. There is a larger percentual distribution of the roots with active metabolism in depth than in the surface of the profile, which stands for, respectively, 31% in the layer of 0.6-0.8 m and 23% in the layer of 0.0-0.2 m. The method also made possible to determine the roots with active metabolism that remained in the soil after sieve, that was 35%, showing the importance of determining these roots.
root system; stable isotope; nitrogen; soil profile
