Successful soil remediation and reforestation of a calcic regosol amended with composted urban waste

Experimental reforestation of highly degraded gypsiferous semiarid soil was successfully carried out after a 400 Mg ha(-1) input of composted urban waste. Changes in soil physical properties, aggregate stability, available nutrients, and seedling growth ( Pinus halepensis, Spartium junceum, Quercus coccifera, Pistacia lentiscus and Santolina chamaecyparissus) were periodically monitored for a 612-day period. The sustained increase in available water ( about 33% in the topsoil and 9% in the 10-20 cm layer) and the lack of toxic effects were important factors in the survival of the four plant species studied. The compost treatment increased soil hydraulic conductivity about 72% in the topsoil and 245% in the 10-20 cm layer and may have played a role in reducing erosive processes (5% slope in the experimental site). The initial effect after compost amendment in the above-noted physical parameters and aggregate stability remained for the entire experiment ( 616 days). The total amount of organic matter (ca. 60 g kg(-1)), the available macro- and microelements, and heavy metals remained relatively constant, indicating that no substantial leaching with negative effects on groundwater contamination had occurred. The parameters showing the most significant changes versus the control plot ( useful for monitoring the transformation extent of the organic matter) were the C/N ratio, the humic acid-to-fulvic acid ratio, and the lipid content, all of which decreased; the concentration of available Mn, Zn, and Cu increased and paralleled aggregate formation; and Na and K concentrations showed a slight decrease by probable leaching. Of the seedlings used, Pistacia lentiscus showed the greatest survival occurring in the presence of compost.