Caracterização e variação temporal da solução do solo em argissolo amarelo com horizonte a moderado e a antrópico ( terra preta de índio) no município de Iranduba- AM

Abstract

Amazonian Dark Earth are known by its typical high fertility and phosphorus contents besides a dark surface horizon designated as Anthropic Horizon . Studies on the nutrients dynamics in the Anthropic Horizons in comparison to neighboring low fertility soils are essential for the comprehension of exchangeable ions capacity and leaching mechanisms in the Dark Earth soils. This study aimed to assess and compare the nutrient dynamics in the soil solution of a Xanthic Kandiudult and Anthropic Xantic Kandiudult. Extracting capsules were installed at the depth of 20 cm, 50 cm and 100 cm (three replicates by each area) for soil solution collecting. Soil samplings from 0 cm to 100 cm depth (20 cm of interval) were obtained by augering for granulometric, chemical and mineralogical soil analyses. Soil bulk densities and pore volume determination were assessed through non deformed samples collected in a soil profile. Clay mineralogy analyses were carried out only in 0-20 and 80-100 cm depths. Soil solution was sampled ten times during the study period for Ca2+, Mg2+, Na+, K+, Al3+, Fe2+, Mn2+, Cu2+ e Zn2+ determinations (acidified samples) and pH and electrical conductivity measurements (non acidified samples). Anthropic Xantic Kandiudult showed higher soil bulk densities and soil water retention values in the field capacity than the Xanthic Kandiudult. Nevertheless the pore volume values were higher in the Xanthic Kandiudult. Anthropic horizons also have higher Ca2+, Mg2+, Mn2+, Zn2+ e Cu2+ contents. Supposing that before antropic activities both soils were physically and chemically similar, it is supposed that human activities reduced the soil bulk density in AB and BA horizons of Xanthic Kandiudult. The mineralogical assemblage of clay fraction is dominated by kaolinite and traces of a mica group mineral and anatase in both soils, demonstrating the same geological material. The Anthropic Xantic Kandiudult shows higher cations contents in CEC and less leaching from solution. An input of nutrients was verified in march 22nd (Ca2+, Mg2+ and Cu2+) and may 31st (K+, Na+, Fe2+, Zn2+ and Mn2+) in the anthropic horizons, what indicates an increasing in the elemental concentration in soil solution via rain and/or desorption from clay and organic matter sites. Organic carbon contents were higher in Xanthic Kandiudult than in Anthropic Xantic Kandiudult. Ca2+ represents the major element in both soils analyzed. Na+ values were the second most frequent in Xanthic Kandiudult solution and in the 50-cm layer of Anthropic layer. Mg2+ values were distinguished only in the 0-20 cm layer of Anthropic Xantic Kandiudult, where reached the second highest value in soil solution. Distinguished values of Mn2+ and Zn2+ were found in Anthropic Xantic Kandiudult, demonstrating equilibrium with CEC of solid phase. Fe2+ values of Anthropic Xantic Kandiudult were significantly lower than Xanthic Kandiudult, what corroborates to previous results. Al3+ concentration in soil solution was null in all evaluated situations in the Anthropic Xantic Kandiudult enhancing the idea of great fertility of these soils