Effects of Coffee arabica cultivation systems on tropical soil microbial biomass and activity in the northeast region of Brazil

Microbial biomass (MB) is an important indicator of soil quality, being responsive to changes resulting from soil management and use. Although there are studies that evaluate changes in soil microbiological attributes in coffee growing systems, the effects of these systems on MB and its relationship with other soil attributes have rarely been investigated, especially in tropical climate conditions at altitude. Therefore, this study aimed to evaluate the effect of different coffee growing systems on biomass and microbial activity and how these responses relate to other soil and litter attributes. Our study was carried out in soils under three Coffea arabica cultivation systems (CCM—monoculture, CCB—consortium with banana, AFS—agroforestry system with Grevillea robusta) and under native forest (NF). Soil samples were collected at a depth of 0–10 cm and subjected to analysis to determine the microbial biomass carbon content (MB-C) by the fumigation-extraction method, accumulated respiration through released CO₂, soil organic carbon (SOC) and labile carbon by wet oxidation. There was a 45% reduction in SOC in coffee growing systems and a 75% reduction in MB-C in CCM compared to NF. The AFS is closer to native forest conditions due to its positive influence on the SOC content and the efficiency of converting this carbon into microbial carbon. The presence of the forestry component is positive and should be encouraged to mitigate the impacts of coffee growing on the soil.