EVALUATION OF PRIMARY FOREST-CAPOEIRA-PASTURE SYSTEMS IN MARABÁ (PA) BY MEANS OF SOIL NITROGEN
Keywords:
Microbial Biomass, Nitrogen, Soil CoverAbstract
Soil microbial biomass (SMB) is an important bioindicator of soil health and plays a vital role in the carbon cycle and the availability of nutrients to plants, which are released as plant organisms decompose. The efficiency of this process is directly linked to microbiological activity, which is influenced by factors such as temperature, humidity, pH, composition, and the C/N ratio. Given this, this study evaluated the impact of different nitrogen fractions on three distinct land use systems (primary forest, secondary forest, and pasture). The areas studied are located on small rural properties in the Benfica Settlement, located in the municipalities of Itupiranga and Marabá, PA. The soil in the study area is dystrophic Yellow Oxisols with a clay texture, and the primary vegetation cover was characterized as dense ombrophilous forest with a climate type of Awi according to the Köppen-Geiger classification. Soil sampling was performed at three depths (0-2 cm, 2-5 cm, and 5-10 cm) in June and October 2004 and February 2005, in a completely randomized experimental design (CRD), with four replicates for each depth. Total N and microbial biomass N (MBN) were determined by chloroform fumigation. The results showed that total N concentrations were higher in forest and secondary forest soils in the surface layer, decreasing with increasing depth. In pastures, the contents were similar between different layers and also showed a reduction in their rates with increasing depth, regardless of age. Regarding microbial biomass nitrogen (MBN), forest and secondary forest soils showed similar values, with no significant changes with increasing depth. In these ecosystems, the greater diversity of species and rapidly decomposing organic matter on the surface favor microbial activity. Pastures, in turn, showed a significant reduction in MBN values compared to forests, ranging from 44% to 75%, depending on the depth and age of the pasture. This shows that the reduction in plant diversity due to the replacement of forest by pastures tends to decrease soil microbial biomass, while secondary forests represented transitional environments between pasture and forest and therefore had the potential for soil condition recovery.
