Abstract
The effects of the application of lime-treated sewage sludge compost on soil chemical properties and soil organic matter (OM) were investigated using soils receiving lime-treated sewage sludge compost for four years at the rates of O, 20, 40 and 60 Mg ha^<-1> year^<-1>. The soils were subjected to chemical analyses and humus characterization, and were separated into four fractions of water-stable aggregates (>1000, 250-1000, 53-250, <53 μm) by slaking of air-dried soil followed by wet sieving. Particulate (>53 μm) and mineralassociated OM (<53 μm) were separated from water-stable aggregates larger than 53 μm by sieving following mechanical dispersion. The application of sewage sludge compost increased significantly the amount of exchangeable Ca^<2+>, and thus resulted in a considerable increase in the soil pH. It also increased signlficantly the amount of soil OM and induced changes in soluble-humus composition. With an increasing rate of compost application, the proportion of the sodium pyrophosphate (NaPP) -soluble fraction increased, while that of the NaOH-soluble fraction decreased. The analysis of humic acid (HA) showed that the application of sewage sludge compost did not affect significantly the humification degree or molecular size distribution of NaPP-soluble HA whereas it induced a significant decrease in the degree of humification and an accumulation of high molecular weight components of NaOH-soluble HA. The OM derived from the applied compost accumulated preferentially in water-stable macroaggregates as particulate OM, but had little effect on the formation of waterstable macroaggregates.
