Vegetation influence on soil quality in a highly degraded tropical soil

The influence of various plant species, two leguminous trees (Andira inermes and Albizia procera), two leguminous covercrops (Arachis glabrata and Centrosema acutifolium), and two grasses (Brachiaria humidicola and Hemarthria altissima), on the soil microbial biomass and abiotic parameters, was evaluated in a highly eroded tropical soil of the Corozal series (clayey, mixed isohyperthermic Aquic Haplohumults). Soil samples were taken monthly at two depths (0- to 5- and 5- to 15-cm) from September 1999 to July 2000. Microbial biomass carbon (MBC), microbial biomass nitrogen (MBN), potentially mineralizable N, extractable N, soil organic matter (SOM), and total organic nitrogen (TON) were significantly greater under grasses. Microbial pools and activities were generally higher at the 0- to 5-cm depth. Soil respiration was significantly affected by plant species and date of sampling; in general, soils under grasses had the highest values. The mean proportions of microbial biomass comprising total organic C and N were 2.8 and 1.4%, respectively, in vegetated soils; higher values for C were observed in bare soil. There was a decrease in the mineralizable C proportion of MBC (respiratory quotient) with increasing MBC values. The lowest respiratory quotients were observed for soils under grasses. In this study, soil ecosystem health appears to benefit from vegetation, with soils under grasses exhibiting improved stability due to higher SOM, TON, biologically active C and N pools and lower relative C losses.