Funções de pedotransferência para padronização de base de dados, critérios de classificação taxonômica e susceptibilidade magnética em Terra Preta de Índio

Abstract

In the Amazon region, soils known as Amazonian Dark Earth (ADE) have as distinctive features the dark colors and high natural fertility. These soils result from the prehistoric intervention of pre-Columbian cultures, which in their occupation added to the soil ceramic and lithic artifacts, coal, food, and bone remains. Over the years, the deposition of this materials led to the development of characteristics different from the non-anthropogenic Amazonian soils, such as the high values of pH (H2O), calcium, magnesium, phosphorus, and carbon stock; resulting in high cation exchange capacity and base saturation of the thick A horizons. These characteristics, coupled with the high stability and reactivity of organic matter, induce the high fertility of ADE, which enticed the interest of scientists for morphological, physical, and chemical studies of these soils. The superficial diagnostic horizon of the ADEs is identified as A antrópico according to the Brazilian Soil Classification System (SiBCS, SANTOS et al., 2018). In the international system of soil classification, the World Reference Base for Soil Resource (IUSS WORKING GROUP WRB, 2014), the Amazonian Dark Earth (ADE) are identified by the pretic diagnostic surface horizon. However, the current quantitative criteria for the anthropic horizon (SiBCS) and the pretic horizon (WRB) failed to classify 50% of the profiles considered as ADE, which were compiled for this work from studies in the Amazon region. Another issue is that the profiles data in the evaluated works presented inconsistencies of some chemical attribute’s units, due to the adoption of different laboratory methods when taking the sample. The different units may influence decisions about the limits of quantitative criteria, mainly for the phosphorus and calcium plus magnesium contents, but no conversion factors were found in the literature that allowed to adjust the difference in these units. Therefore, pedotransfer functions (PTFs) were developed to perform such conversions and to harmonize the chemical database, adjusting the different units used in the compiled studies. The PTF with higher precision, i.e., with the smallest RSE (0.092 g cm-3), was the one using total sand content to predict the density of the fine earth, essential for the conversion of the data. Subsequently, the data were evaluated and quantitative taxonomic criteria were proposed for the SiBCS Anthropic horizons and for the WRB pretic horizon. The soil profiles reclassification, according to the proposed criteria, shows that 84% of the profiles were included as A antrópico and pretic horizon, respectively in SiBCS and WRB. Additionally, 81% of the profiles were classified as Anthrosols in the WRB, according to the new criteria. Another aspect mentioned in the literature about ADEs is the high magnetic susceptibility (MS), which is related to changes in the structure of the soil minerals caused by heating when fire (burning, bonfires) is used during the period of human occupations. MS can be quickly analyzed through the use of proximal sensors, thus resulting in another way to identify pre-historic human occupation sites. In a preliminary study at the Experimental Research Field of Caldeirão, municipality of Iranduba (AM), the MS of samples of soil layers identified as anthropic and non-anthropic was evaluated. The classification of the samples followed the current WRB criteria for the Pretic horizon. In the anthropic samples, the MS values were higher, and there was a positive and high correlation between the SM and P and Zn levels, differently from the non-anthropic samples.