Changes in soil microbial biomass and activity in different Brazilian pastures

Microbial biomass and activity are useful indices for assessing changes in soil ecosystems. The impact of different pastures on microbial biomass and activity was studied in a long-term experiment in Northeast Brazil. For our study the pastures were divided into plots: a) Brachiaria brizantha; b) Leucaena leucocephala; c) Cynodon dactilon; d) Panicum maximum. An adjacent area with native vegetation was used as reference. Soil samples were collected in 0-10 and 10-20 cm depths. No significant differences in soil organic C (C-org) was found among all plots at 0-10 and 10-20 cm depth. Soil microbial C (C-mic) values were higher in native forest and P maximum when compared to the other plots. The soil basal respiration (CO2) values were similar among all plots evaluated. However, respiratory quotients (qCO(2)) were significantly lower in native forest and P. maximum when compared to other plots, at 0-10 cm depth. Values of fluorescein diacetate (FDA) hydrolysis were significantly higher in native forest and P maximum, while values of dehydrogenase activity were found to be significantly higher in native forest, C. dactilon and P maximum. Soil microbial biomass and activity changed when a native forest was converted to pastures. These changes were positive with the inclusion of maximum by the high input of C sources.