Cyclic utilization of sludge and flyash to improve the soil quality in karst rocky desert

Soil in karst rocky desert is applied with sludge-flyash composites of different sludge to flyash proportion in this experiment, and the effects of sludge-flyash composites on soil physicochemical properties, water-holding capacity and heavy metal accumulation in Festuca arundinacea are studied accordingly. The results show that the heavy metal contents like Cu, Mn, Zn and Cd in the sludge are remarkably decreased, the soil pH enhanced to about 7 and the soil physicochemical properties improved obviously after applying flyash; and that the soil water-saturation coefficients is enhanced by 1.95 times, the time of water retention elongated about 7d, the soil N, P increased and the biomass of Festuca arundinacea is also enhanced remarkably. So, it can yet be regarded as an effective method to ecologic rehabilitation for karst rocky desert. But it is not suitable to apply sludge repeatedly for the half-life period of the heavy metals in the sludge is long and the heavy metals are difficult to be thoroughly eliminated, and the heavy metals themselves are of serious eco-toxicity.