THE INFLUENCE OF COMPOSTING ON THE FERTILIZING VALUE OF AN AEROBIC SEWAGE-SLUDGE

The influence of composting on the fertilizing value of an aerobic sewage sludge and its action on ryegrass was studied. Soil P and K contents, cation-exchange capacity (CEC) and CEC/total organic carbon increased with composting, while the percentage of phytotoxic substances diminished. The compost provided useful quantities of organic matter and macronutrients. The addition of uncomposted waste to the soil initially had a depressive effect on yield which disappeared after a period of incubation of this material in the soil, whereas the application of a mature compost produced yields superior to those in the control treatment.