Laser-induced fluorescence of organic matter from a Brazilian Oxisol under sewage-sludge applications

Martha González Pérez,Débora Marcondes Bastos Pereira Milori,Luiz Alberto Colnago,Otávio Antonio De Camargo,Ronaldo Berton,Wagner Bettiol,Ladislau Martin-Neto

doi:10.1590/s0103-90162006000300009

Abstract

Sludge applications have been used to maintain fertility of agricultural soils without damaging the natural ecosystem. The aim of this study was evaluating the influence of sewage-sludge addition on the quality of organic matter (OM) of a Brazilian Oxisol by Laser Induced Fluorescence (LIF). LIF was used to analyze OM of whole soil and different soil fractions separated by chemical and physical methods. The high fluorescence contribution of humin fraction to the fluorescence of whole soils was shown, stressing the importance of studying OM associated to mineral matrix of soil. Spectra with different shapes were obtained for every particle size fraction, indicating differences in organic compounds bounded to them. The fraction with the higher carbon content was the 2-20 µm, that contains ~5% C and represents only 10% in soil, but stores 34-39 % of total C and shows the highest fluorescence intensity. The spectrum of this fraction shows its heterogeneity and a higher concentration of compounds which fluorescence is centered at 510 nm. This indicates a higher concentration of unsaturated bond systems capable of high degree of resonance, increased conjugation of the electron pi system, and higher aromaticity comparing with other fractions. No differences were detected for treatments of sewage-sludge applications. LIF spectroscopy is a promising technique for OM studies in whole soils, allowing to study spatial distribution of OM within the soil's mineral matrix, including Oxisols.

Highlights

IntroductionOne of the agricultural priorities is to sustain and maintain fertility levels of soil without damaging the natural ecosystem
One of the agricultural priorities is to sustain and maintain fertility levels of soil without damaging the natural ecosystem. Alternatives such as sludge applications have been recommended to achieve this ob
Emission spectra of some whole soil samples are shown in the Figure 1a

Summary

Introduction

One of the agricultural priorities is to sustain and maintain fertility levels of soil without damaging the natural ecosystem Alternatives such as sludge applications have been recommended to achieve this ob-. Sludge is a significant source of supplementary nitrogen, phosphorus and other essential nutrients for plant growth. Once it incorporates high quantities of organic matter (OM) that improve fertilization level and some physicalchemical properties of soils in land restoration (Melo & Marques, 2000; Piccolo et al, 1992), their disposal on agricultural soils has been strongly promoted. In addition to these agricultural benefits, the incorporation of organic amendments and crop residues into the soil, in some situations, can reduce emissions of CO due to carbon fixation, with meaningful implications for mitigation of the greenhouse effect (Bayer et al, 2000)

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