Abstract
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.
Highlights
Amazon rain forest soils are thought to have a very high microbial biodiversity, since they support one of the most species rich ecosystems on the planet
The objective of this study was to assess changes in levels of microbial C and mineral N, nitrate N ( NO− ) and ammonium ( NH+ ), and soil nutrients, in agroforestry systems and other land uses with different plant cover during the wet and dry seasons, in areas managed by indigenous communities and small farmers in the Alto Solimões region, Amazonas State, Brazil
The chemical composition of soils studied show that the levels of nutrients in the soil layer measured are above the average of most soils in Amazonia [27] [28]
Summary
Amazon rain forest soils are thought to have a very high microbial biodiversity, since they support one of the most species rich ecosystems on the planet. Soil quality is the most important link between agricultural practices and sustainable agriculture [3]. In this regard, indigenous people and small-scale farmers in the Amazon who use practices of slash and burn have been encouraged to adopt techniques that promote nutrient cycling and maintain soil organic matter (SOM) in order to conserve or improve soil quality. The microbial biomass is an SOM compartment which proportionally represents the smallest fraction of soil organic C, but is a significant and potentially mineralizable source of N available to plants [5], showing fast nutrient cycling and responding intensely to seasonal fluctuations in humidity and temperature, farming practices and management of plant residues [6].
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