Abstract:
A field study was conducted on two texturally different soils to determine the influences of biosolids
application on selected soil chemical properties and carbon dioxide fluxes. Two sites, located in Manildra
(clay loam) and Grenfell (sandy loam), in Australia, were treated at a single level of 70 Mg ha 1 biosolids.
Soil samples were analyzed for SOC fractions, including total organic carbon (TOC), labile, and non-labile
carbon contents. The natural abundances of soil d13C and d15N were measured as isotopic tracers to
fingerprint carbon derived from biosolids. An automated soil respirometer was used to measure in-situ
diurnal CO2 fluxes, soil moisture, and temperature. Application of biosolids increased the surface (0
e15 cm) soil TOC by > 45% at both sites, which was attributed to the direct contribution from residual
carbon in the biosolids and also from the increased biomass production. At both sites application of
biosolids increased the non-labile carbon fraction that is stable against microbial decomposition, which
indicated the soil carbon sequestration potential of biosolids. Soils amended with biosolids showed
depleted d13C, and enriched d15N indicating the accumulation of biosolids residual carbon in soils. The in-situ respirometer data demonstrated enhanced CO2 fluxes at the sites treated with biosolids, indicating
limited carbon sequestration potential. However, addition of biosolids on both the clay loam and sandy
loam soils found to be effective in building SOC than reducing it. Soil temperature and CO2 fluxes,
indicating that temperature was more important for microbial degradation of carbon in biosolids than
soil moisture.
