SOIL CHEMICAL CHANGES AND RESEMBLANCES IN A CHRONOSEQUENCE RAINFOREST-SUGARCANE-PASTURELAND IN THE ATLANTIC FOREST BIOME

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.