Microbial biomass and cellulase activity in soils under five different cocoa production systems in Alto Beni, Bolivia

Cocoa is one of the most important crops of the Alto Beni region in Bolivia. This crop is produced in different systems, among them monoculture and agroforestry. In order to determine the effect of the production system on microbiological soil characteristics, we measured microbial biomass carbon, microbial biomass nitrogen and cellulase activity and we determined the microbial quotient in soil under five different cocoa production systems (conventional monoculture, organic monoculture, conventional agroforestry, organic agroforestry and successional agroforestry) and in fallow plots. The measurements were carried out in dry and rainy season. Soil from fallow plots and soil under agroforestry had higher microbial biomass than soils under monocultures, probably due to the effect of fresh organic matter input on microbial biomass. No significant difference for microbial biomass in soil from plots subjected to organic management and soil from plots subjected to conventional management was observed, possibly because of the short time elapsed from the initial establishment of the plots. In dry season, the microbial quotient showed a significantly higher value in soils under conventional agroforestry than in soils under organic monoculture, suggesting that besides the input of fresh organic matter, mineral fertilization may play a role on the fraction of available carbon. Cellulase activity was not affected by any of the factors tested, indicating that, under our assay conditions, it was not a good indicator of changes in soil.