Impact of coffee biochar on carbon, microbial biomass and enzyme activities of a sandy soil cultivated with bean oleh ARGEMIRO P. MARTINS FILHO, ERIKA V. DE MEDEIROS, JOSÉ ROMUALDO S. LIMA, DIOGO P. DA COSTA, GUSTAVO P. DUDA, JENIFER S.A. DA SILVA, JULYANA B. DE OLIVEIRA, ANTÔNIO C.D. ANTONINO, RÔMULO S.C. MENEZES, CLAUDE HAMMECKER