Microbial Carbon, Mineral-N and Soil Nutrients in Indigenous Agroforestry Systems and Other Land Use in the upper Solimões Region, Western Amazonas State, Brazil

Slash and burn cultivation systems carried out by many farmers in the Amazon region lead to changes in biogeochemical cycles of nutrients. To assess the extent of the impact of shifting cultivation on the soil in a floodplain portion of this region, samples of an Inceptisol surface layer (0 - 5 cm) under primary forest (FP), secondary forest at an advanced stage of recovery (FS), secondary forest at an initial stage of recovery (CAP), agroforestry (SAF), plantations (R?) in indigenous communities and small farmers, and pasture (PAS) in the Upper Solim?es region, Amazonas, were subjected to analysis of chemical composition during the wet (May) and dry (October) seasons, 2007. Soils were fertile with levels of P, K, Ca and Mg above those generally found in Amazon soils. Microbial content did not vary significantly in the systems studied in the wet season, but there was a reduction of around 60% with the change of season, except for soils with SAF. Ammonium nitrogen was predominant in all systems and seasons studied. Nitrate content was higher in R? soil, in two seasons, and lower in PAS. The type of management adopted by farmers in the region’s indigenous agroforestry systems resulted in small changes in P, K, Mg, MBC and mineral-N levels, independent of soil moisture.

Microbial enzymatic stoichiometry and the acquisition of C, N,and P in soils under different land-use types in Braziliansemiarid

This study hypothesized that different land-use affect the microbial enzymatic stoichiometry and C-,N-,and P-acquisition in Brazilian semiarid soils.Thus,the enzymesβ-glucosidase(C-acquiring enzyme),urease(N-acquiring enzyme),and acid phosphatase(P-acquiring enzyme)were assessed in soil samples collected at 0−5 and 5−10 cm depth from a tropical dry forest,a protected area with Angico,a protected area with Ipê,scrub area,and an agricultural area with maize.The values of C-,N-,and P-acquiring enzymes were used to calculate the enzymatic C:N,C:P,and N:P ratios.The values of C:P and N:P ratios were higher at 0−5 cm depth,while no significant variation,between soil depth,was observed for C:N ratio.The values of C-and N-acquiring enzymes were higher at 0−5 cm in tropical dry forest areas and Angico forest,respectively.In all land use types,the values of vectors L and A were higher than 1°and 45°,respectively.This study showed that both land-use and soil depth influence the enzymatic stoichiometry,showing higher values of C-and N-acquiring enzymes in native and protected forests at soil surface.