Análises espectroscópicas da matéria orgânica de solos sob aplicação de águas residuárias / Spectroscopic analyses of soil organic matter under irrigation with trated wastewater

AUTOR(ES)
DATA DE PUBLICAÇÃO

2008

RESUMO

Around the world there is a growing competition for the use of water among several sectors of society. Water consumption in agriculture is large when compared to other types of use and can affect the availability of water for the urban population unless it is well administered. In Brazil, agriculture consumes about 61% of the total freshwater. Among the different ways tried by contemporary societies to solve or minimize this problem, aiming to use rationally and efficiently this precious natural resource, reuse of wastewater (effluents) is an economically viable and environmentally correct option. The aim of this work was to study the changes in organic matter in a Typic Hapludults cultivated with Tifton 85 Bermudagrass submitted to addition of effluent generated by sewage treatment. The utilized samples were collected at Lins / SP, being part of a previously started experiment. The experimental design employed was the randomized complete blocks, with six treatments and three replications. The analyzed six treatments were: (1) WI - without irrigation and without nitrogen as mineral fertilizer (NMF) - (white), (2)E100 - irrigation with effluent and 100% (520 kg ha-1 year-1) of the recommended dose of NMF for the Bermudagrass Tifton - 85, (3) E66 - irrigation with eflluent and 66% (343.2 kg ha-1 year-1) of the NMF, (4)E33 - irrigation with effluent and 33% (171.6 Kg ha-1 year-1) of the NMF,(5) E0 - irrigation with effluent and 0% (0 kg ha-1 year-1) of the NMF,(6) W100 - irrigation with water for consumption and 100% (520 Kg ha-1 year-1) of the NMF. Humic acids (HA) were extracted from these samples in order to observe the effects of adding treated sewage effluent (TSE) using nuclear magnetic resonance of 13C (13C NMR) spectroscopy, Fourier transform infrared (FTIR) spectroscopy, UVvisible and fluorescence spectroscopy, electronic paramagnetic resonance (EPR) spectroscopy and elementary analysis (C, H, N, S). In order to analyze the whole soil, laser induced fluorescence (LIF) was utilized, and the carbon levels were determined through total organic carbon (TOC). Through the results obtained by elementary analysis, FTIR and 13C NMR, it was not possible to obtain information about changes in the composition of HA after adding the TSE, because these techniques were not sensitive to changes in OM. Both 13C NMR and FTIR provided spectra with bands typical of aliphatic groups, showing their high degree of aliphaticity. The fluorescence spectroscopy results for samples in solution demonstrated that the irrigation with TSE increases both the concentration of complex structures and the humification degree of HA. The results of LIF for the whole soil, however, showed no significant change with irrigation with TSE (except for the treatment E33), indicating that changes of humic substances in the analyzed soil occurred mainly in HA, and affecting very little on humin, which represents more than 80% of the soil HS. The results obtained by EPR demonstrated that the treatments irrigated with TSE showed an increase in the concentration of semiquinone-type free radicals, with increasing fertilization, except for the treatment E33. Therefore, regarding SOM, irrigation with TSE along a four years period did not cause significant changes, and, under this viewpoint, it can be indicated as an alternative irrigation not significantly impacting the organic matter and providing economic, environmental and social benefits.

ASSUNTO(S)

matéria orgânica águas residuárias ácido húmico humic acid wastewater organic matter

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