Responses of soil microbial biomass and activity for practices of organic and conventional farming systems in Piauí state, Brazil

The aim of this work was to investigate the response of soil microbial biomass and activity to practices in organic and conventional farming systems. The study was carried out at the Irrigation District of Piauí, Brazil. Five different plots planted with “acerola” orchard (Malpighia glaba) and established at the following management were evaluated: (1) under 12 months of soil conventional management (CNV); (2) under six months of soil organic management (ORG6); (3) under 12 months of soil organic management (ORG12); (4) under 18 months of soil organic management (ORG18); and (5) under 24 months of soil organic management (ORG24). Soil microbial biomass C (Cmic), basal respiration, organic carbon (Corg), Cmic-to-Corg ratio and metabolic quotient (qCO2) were evaluated in soil samples collected at 0–10 cm depth. The highest Corg and Cmic levels occurred in organic system plots ORG18 and ORG24 compared to the conventional system. Soil respiration and Cmic-to-Corg ratio were significantly enhanced by the organic system plots. The qCO2 was greater in conventional than in organic system. These results indicate that the organic practices rapidly improved soil microbial characteristics and slowly increase soil organic C.