Effects of amendment with composted sludge on soil humic acid properties

The main physical and chemical properties of a composted mixture of sewage sludge and wood chips, the nonamended soil, and soils amended with two rates of the compost, in the presence or absence of barley, were determined. Humic acids (HAS) isolated from these materials were characterized by various methods including elemental analysis and Fourier Transform infrared (FTIR), fluorescence, and electron spin resonance spectroscopies. With respect to the nonamended soil HA, the compost HA was characterized by a prevalent aliphatic character, low oxygenated functional group content, high contents of S, N-containing groups and polysaccharide components, low free radical concentration, high molecular heterogeneity, and low degrees of ring polycondensation, polymerization and humification. Compost application at the low rate appeared to induce only limited modifications in the structural and chemical properties of HAS from amended soils, whereas apparent modifications of HA properties occurred where a high amendment rate was used. The absence or presence of barley cultivation appeared not to exert any measurable effect on the composition and properties of compost-amended soil HAS.