Soil enzymatic activities and microbial biomass in an integrated agroforestry chronosequence compared to monoculture and a native forest of Colombia

Large tracts of land in South American native forests have been converted to monoculture for livestock production which could negatively affect soils and environmental quality. A proposed management alternative is to use agroforestry systems, but little information is available on how they affect the soils. The objective was to assess the effect of a silvopastoral chronosequence in a tropical region of Colombia on soil microbiological and physico/chemical properties. The systems (three replications) were: monoculture grass conventional pasture (CP), native forest (F), and a silvopastoral system (SS) chronosequence with ages of 3 to 6 (SS₃), 8 to 10 (SS₈), or 12 to 15 (SS₁₂) years. Soil responses to these land management were determined by measuring soil chemical (total C and pH), physical (penetrometer resistance and bulk density), and microbiological properties (activities of ß-glucosidase, urease, and alkaline and acid phosphatase and microbial biomass). Because of differences in soil texture across management treatments, microbiological properties were normalized on organic C content basis. SS₁₂ showed the highest microbial biomass and enzyme activities on a per unit C basis and was consistently and significantly different from CP. Additionally, microbiological to C ratios were significantly affected by SS establishment age (P < 0.05). The low microbiological responses were consistent with high penetration resistance and bulk density of CP which indicates that the SS are improving soil quality. This study presented quantitative data that SS stimulated soil microbial biomass and enzyme activities, which indicates greater potential to carry out biogeochemical process, and that SS provides a more favorable microbial habitat.