Spatial variability of soil erodibility in pastures and forest areas in the municipality of Porto Velho, Rondônia oleh Lucivânia Izidoro da Silva, Milton César Costa Campos, Wildson Benedito Mendes Brito, José Maurício da Cunha, Alan Ferreira Leite de Lima, Luís Antônio Coutrim dos Santos, Abdul Luís Hassane