This study aims to evaluate the effect of land cover type, soil properties, and vegetation structure on fine root biomass, and examined how these factors affect diameter of fine roots. The study was conducted in communities located in the Nova Ipixuna, Parauapebas and Pacajá municipalities of Pará state. In each area, nine farms were selected; in each farm were sampled five plots, totaling 135 plots distributed into nine different types of land cover; at each plot, four soil samples were collected to quantify the fine roots, vegetation cover was inventoried, and soil was collected for physical and chemical characterization. Fine roots were separated into four different classes. Principal Component Analysis (PCA) were done for the soil and vegetation matrix and they were compared with the fine root biomass PCA through a co-inertia analysis. Variability was high for fine root biomass data. All land covers exhibited a high proportion of fine roots > 1 mm. The co- inertia analysis showed that the fine root biomass PCA share a common structure with vegetation PCA, with 37/100 of the variability being explained; however only 9/100 of the variability was explained by the soil PCA. Our results highlight the importance of roots with diameters < 2 mm for the quantification of root biomass, whereas the biomass of roots > 2 mm was critical to the differentiation among land covers.