FATE OF "PASTAZZO" AND COMPOST ORGANIC MATTER IN SOIL AS DETERMINED BY ISOELECTRIC FOCUSING AND 13C NMR SPECTROSCOPY.

An incubation experiment on two different organic matrices mixed to a soil was carried out to monitor changes in the chemical composition of organic matter. Aim of the experiment was the knowledge of chemical changes occurring to organic matter added to soil due to stabilization processes. A control soil without any addition, a mixture of the same soil plus compost, and a mixture of the same soil plus "pastazzo" (an Organic residue from industrial processing citrus fruits) were incubated in microcosms under controlled conditions of temperature and moisture. Sub-samples, taken from the microcosms at start of the experiment and fixed times during incubation, were analyzed to determine total organic carbon and humification parameters; then, they were extracted with NaOH and Na₄P₂O₇, and the extracts were analyzed by CP-MAS ¹³C NMR and iso-electric focusing (JEF). IEF showed that the bandwidth of peaks produced by focused material on the right side of the profile increased by increasing incubation time, probably due to stabilization of the samples. The ¹³C NMR spectra of pastazzo seem to demonstrate its organic matter was completely mineralized by the gradual disappearance of its characteristic peaks, compared with those of the untreated soil. On the contrary, the spectrum characteristics of the compost were still recognizable after 2-years incubation, demonstrating higher stability. in all samples, an extra peak appeared after 6 months at nearly 170 ppm, corresponding to the area of the carboxylic groups, probably due to the production of esters. Both techniques can be used to profitably monitor transformations of organic residues when added to soil, specially by integration of the information obtained about the humification level suggested by IEF with the chemical characteristics of the samples determined by NMR. [ABSTRACT FROM AUTHOR]