A long‐term field experiment was conducted to determine the effect of the additions of urban waste compost on the physical and chemical properties and enzymatic activities in a calcareous soil (Fluventic Xerochrept). Total porosity (pores >50 µm measured on thin soil sections from undisturbed samples by image analysis) was greater in the plots treated with compost than the control plots due to a larger amount of elongated pores. In the amended plots total and humified organic C, Pb, Cu, and Zn showed a significant increase compared with nonamended plots. Enzymatic activities (L‐asparaginase, arylsulphatase, dehydrogenase, phosphodiesterase, and alkaline phosphomonoesterase) were significantly enhanced by the compost addition thus indicating no inhibiting influence of the heavy metals present. The increased levels of the arylsulphatase, dehydrogenase, phosphodiesterase, and phosphomonoesterase activities were significantly correlated with total porosity: the first three with pores ranging from 50 to 1000 µm, mainly with pores 50 to 200 µm in size, and phosphomonoesterase only with pores whose size was <500 µm. L‐asparaginase activity was not correlated with porosity. Only arylsulphatase, dehydrogenase, and phosphodiesterase were negatively correlated with bulk density.
The characterization of pig sludge liquid fraction (PSLF) was conducted to achieve a better understanding of its chemical and physical chemical characteristics. Total dissolved organic carbon (TDOC) from pig sludge was separated into two fractions: acid insoluble dissolved organic carbon (AIDOC) and acid soluble dissolved organic carbon (ASDOC). Elemental analysis, acidic functional group determination, E4/E6 ratio, Gel‐Filtration Cromatography and FTIR Spectroscopy of ASDOC and AIDOC showed a similarity with humic and fulvic acids, isolated from soils and organic wastes. Phosphorus‐31 Nuclear Magnetic Resonance spectra demonstrated that the organic P in PSLF was present as P‐monoester. The complexing capacity of DOC vs. trace metals was demonstrated by Gel Filtration Chromatography and FTIR Spectroscopy. The interactions of DOC, Cu, and Zn, present in PSLF, with a calcareous soil were evaluated by adsorption isotherms that indicated that Zn was completely adsorbed by the soil, while Cu followed the same behavior as DOC, with only partial adsorption. Therefore, both Cu and DOC should be taken into consideration as a possible groundwater pollution hazard after pig sludge application to calcareous soil.
A soil column study was conducted to assess the vertical movement of certain heavy metals in soils amended with urban waste compost (90 t ha−1). The effect of the complexing capacity of water soluble organic matter from compost on metal mobility has been previously reported. The results of this investigation demonstrate the enhanced levels of Cu, Zn, Ni, and Cr eluted from 50‐cm soil columns when compost is added to a Fluventic Xerochrept clay‐loamy, mixed, mesic and a Typic Xerochrept, fine sandy‐loamy, mixed, mesic. The increase in these metal concentrations is greater in sandy‐loam soil than in clay‐loam. The water soluble organic fraction of the compost has minimal impact on the metals concentration. Seventy to eighty percent of the water‐soluble organic fraction was retained in the upper 10‐cm layer of soils, with only 5% eluted from clay‐loam soil and 10% from the sandy‐loam.
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