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Abstract
This study evaluated soil chemical and isotopic changes in soils of a chronosequence rainforest-sugarcane-pasture in the Atlantic Forest biome, Brazil. Soil samples were collected (0-20 cm) in areas of native Brazilian Atlantic rainforest, sugarcane plantation and pastures of Brachiaria decumbens. The soil analyses performed were: pH (water 1:2.5), P (Mehlich-I), (Al+3, H+Al, K+, Ca+2, Mg+2 and Na+), soil organic matter (SOM), N, organic carbon and δ13C and δ15N stable isotopes. The conversion of rainforest to sugarcane and pastures resulted in a reduction of the soil natural acidity. Forest areas had greater Al+3 and H+Al concentrations than cultivated areas. The conversion from forest to agricultural soil reduced Al+3 (44%) and H+Al (11%), approximately. Soils from pasture had a greater percentage of base saturation (37.3%) than forest soils (25.4%). Cation exchange capacity was strongly influenced by concentrations of K+, Ca+2 and Mg+2, but not by Na+. Carbon stable isotope (δ13C) was more depleted in forest areas (-28.14‰), followed by sugarcane (-21.33‰), and pastures (-19.54‰). The greatest δ15N values were found in sugarcane areas. The short chronosequence studied, had a strong influence of the conversion of the forest on the decrease of the natural acidity and modifications of the isotopic profile. The enrichment of soil δ13C was attributed to the changes from predominant C3 vegetation to C4 grasses.
Highlights
The conversion of native vegetations into agricultural lands is considered one of the main factors that can drastically impact changes in the physical-chemical and biological characteristics of the soil
Due to intrinsic characteristics of each type of native vegetation and soil that was subjected to the conversion of its natural cover, as to the different types of crops/agricultural system adopted after conversion, these soil alterations might have a different pattern according to each specific case
The greater concentrations of Al+3 and H+Al in forest soils effectively contributed to their lower pH levels compared to sugarcane and pasture soils
Summary
The conversion of native vegetations into agricultural lands is considered one of the main factors that can drastically impact changes in the physical-chemical and biological characteristics of the soil. Due to intrinsic characteristics of each type of native vegetation and soil that was subjected to the conversion of its natural cover, as to the different types of crops/agricultural system adopted after conversion, these soil alterations might have a different pattern according to each specific case. In the last decades, sugarcane production in Northern Brazil stagnated in its productivity and competitiveness, while the sugarcane production in Southern Brazil expanded due to higher levels of competitiveness (Rudorff et al, 2010; Moraes et al, 2016) These factors combined, have contributed to the conversion of sugarcane areas into other crops cultures or pasturelands in Northern Brazil
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