Abstract

ABSTRACT In the Amazon region, soil patches with an anthropic A horizon are found, called Indian black earths (IBEs). Indian black earths are highly fertile and, therefore, are deforested by small local farmers to cultivate without basic management that maintains soil and crop sustainability. Therefore, in order to evaluate the effect of using different cultures on the spatial variability of soil chemical attributes, three cultivated IBEs and one IBE under natural forest were selected for georeferencing and sample collection. The collection was made with a mesh system with 88 points per IBE, stratified in three layers: 0–0.05, 0.05–0.10 and 0.10–0.20 m. The soil was sampled, dried in the shade and sieved to obtain the fine earth fraction for analysis of chemical attributes. Descriptive statistical and geostatistical analyses were applied to the results. The use and management of soil influenced the spatial behavior of the chemical attributes of IBEs. The cultivation of Brachiaria over many years favored the reduction of the spatial variability of chemical attributes. The use of cacao and coffee crops also favored the homogeneity of the IBEs in relation to the natural forest, but not as much as for Brachiaria, likely due to the succession of crops that preceded these crops. The IBE in the forest contains a high natural spatial correlation in the first 0.1 m of the surface; however, more than 70% of this correlation is linked to a random variation.

Highlights

  • Human-modified soils are recognized as anthrosol or anthroposols according to the World Reference Base (FAO 2015), or are part of soils with anthropic A horizons (Santos et al 2018)

  • The Indian black earths (IBEs) in the forest contains a high natural spatial correlation in the first 0.1 m of the surface; more than 70% of this correlation is linked to a random variation

  • The IBE cultivated with cacao showed greater fertility, the IBE of Brachiaria shows organic carbon (OC) levels higher than the other IBEs, which it is concluded that comes from the root system and the greater soil coverage by its culture

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Summary

Introduction

Human-modified soils are recognized as anthrosol or anthroposols according to the World Reference Base (FAO 2015), or are part of soils with anthropic A horizons (Santos et al 2018). The Indian black earths (IBEs) are distributed in discontinuous patches across the Amazon, being normally located at an interval of 5 to 25 m in height in relation to water courses, and can occur in areas higher than 40 m in altitude for places that required better visualization of the area. Still, they have the peculiarity of maintaining high fertility even after successive years of cultivation, even with little or no replacement of nutrients (German 2003; Kern et al 2017; Teixeira et al 2009). Both attribute values and their variability characteristics can be affected by management (Kravchenko et al 2005)

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