Abstract
Amazonian soils have some physical, chemical and mineralogical differences, understanding the differences is important to understand the behavior of nutrients in the soil, especially phosphorus. The study was carried out in two types of soils: a Hydromorphic soil profile and a Non-hydromorphic soil profile in the Central Amazon region of Brazil, located in the metropolitan area of Manaus. Five depths were sampled: 0.00-0.05; 0.05-0.1; 0.1-0.2; 0.2-0.4; and 0.4-0.6 m. Physical, chemical, mineralogical and morphological attributes of both soils were studied. With the exception of clay, the levels of sand and silt remained stable in depth. The levels of organic matter gradually decrease in depth. The pH in water and in KCl, ∆pH, point of zero load, were similar between the surface and subsurface soils. Al3+, H++Al3+, CECt, CECT and clay activity were similar in Non-hydromorphic soil and increase in surface (< 0.2 m) and stabilize in subsurface (> 0.2 m). In both soils, the bases are reduced in subsurface (> 0.2 m). Aluminum and iron oxalate reduce with greater expressiveness in Non-hydromorphic soil. Aluminum and dithionite iron exhibit the same behavior. The levels of Goethite (Gt) and Hematite (Hm) are high in depth in the Non-hydromorphic soil and decrease in the Hydromorphic soil. There are sensitive distinctions between soils, due to the imposed edaphoclimatic conditions.
Highlights
The soils of the Amazon, mainly those of the Central Amazon, are predominantly formed by the weathering of sedimentary rocks
The characteristics of the source material combined with the intense edaphoclimatic action typical of the region of origin, in general, deep soils and without significant physical impediments, chemically poor, which in part represent a barrier to local development (Sanchez et al, 1982; Falesi, 1984; Lima, 2001)
In the Dystrophic Gleysol Haplic (GHd), the color is changed from 5 YR 5/8 to 5 YR 8/2, due to the process of gleization, in which there is chemical and mineral reduction of Fe in the absence of oxygen (O2) for a certain period and, its exit from the soil section (Schaefer et al, 2017)
Summary
The soils of the Amazon, mainly those of the Central Amazon, are predominantly formed by the weathering of sedimentary rocks. The characteristics of the source material combined with the intense edaphoclimatic action typical of the region of origin, in general, deep soils and without significant physical impediments, chemically poor, which in part represent a barrier to local development (Sanchez et al, 1982; Falesi, 1984; Lima, 2001). Not being a static process, the formation of soils is subject to variations imposed by the environment, so that soils with similar geomorphological origin can be influenced by the environments in which they are inserted, promoting distinct chemical, physical and mineralogical characteristics (Moreira & Vasconcelos, 2007; Vale Júnior et al, 2011). In the Floodplain, mainly in the Solimões River, there is a predominance of soils that present natural drainage restrictions during part or all of the year, known as hydromorphic soils (Lima, 2001; Teixeira et al, 2010). According to Teixeira et al (2007), Gleisols represent up to 60% of the soils present in jas.ccsenet.org
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