HUMIC ACIDS ISOLATED FROM TWO BIOSOLID-AMENDED BRAZILIAN OXISOLS

摘要

In the last decades the production of urban-industrial residues is continuously increased.The biosolid use as source of plant nutrients and organic matter in agricultural soils is considered a good alternative to its expensive disposal in sanitary or industrial landfills.This issue is particularly relevant in metropolitan regions,such as Sao Paulo city,Brazil,whose population generates nearly 15 m~3 s~(-1)sewage(about 235 Mg day~(-1)biosolid).Further,countries dominated by tropical climate are subjected to an increasing impoverishement of soil organic matter(SOM)due to both the fast turnover rate and deforestation for grazing,cropping and industrial purposes.On these bases,SOM plays a major role in tropical soil productivity representing the main reservoir of plant nutrients,and is often considered to be the most important source of cation exchange capacity(CEC)in tropical soils dominated by kaolinite and amorphous oxides(Zech et al.,1997).Although the positive effects of organic amendment to weathered tropical soils are well known,there is little information about its impact on native soil humic fractions.The aim of this work was to investigate the effect of biosolid application on the compositional,structural and functional properties of native soil humic acids(HA)by comparatively studying the chemical and spectroscopic characteristics of HAs isolated from two Brazilian Oxisols amended with a biosolid with respect to those of HAs from the corresponding unamended soils.