Soil carbon stock and Plinthosol fertility in smallholder land-use systems in the eastern Amazon, Brazil
dos Santos, Ceália Cristine | Souza de Lima Ferraz Junior, Altamiro | Oliveira Sá, Sandra | Andrés Muñoz Gutiérrez, Jhonatan | Braun, Heder | Sarrazin, Max | Brossard, Michel | Desjardins, Thierry
The soil organic carbon (SOC) stock is an important attribute in the maintenance of ecosystem services by natural and agricultural ecosystems. In the humid tropics, slash-and-burn cultivation for food production and establishment of pastures has frequently led to soil degradation. In the eastern Brazilian Amazonia, we assessed impacts of different land-use systems on the SOC stock and some chemical properties of soils. Four land-use systems were studied: shifting cultivation (SC), pasture (PA), mixed fallow (MF) and secondary forest (SF). In the soils studied, most nutrients were not significantly influenced by land-use changes, and the chemical fertility was low. Similarly, SOC concentration was low, ranging, in the 0-10 cm layer, from 9.54 g kg⁻¹ in PA to 12.73 g kg⁻¹ in MF. In the 0-100 cm layer, the SOC stock varied from 42.1 Mg ha-1 in SC to 53.3 Mg ha⁻¹ in MF, without significant differences between the land-use systems. The SOC stock in the 0-30 cm layer represented 50-56% of that in the 0-100 cm layer. The soils studied have the lowest SOC stocks measured in the Amazonia region. The low organic matter content, associated with soil acidity, a small sum of exchangeable bases and low extractable P, can constrain the productivity and the sustainability of these cropping systems.
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