INFLUENCE OF SEWAGE-SLUDGE APPLICATION ON CROP YIELDS AND HEAVY-METAL AVAILABILITY

A calcareous soil with a low content of organic matter was treated with aerobic or anaerobic sewage sludge. In the same way, chicken manure was used for comparison. Influences on crop yields and the supply of macronutrients and heavy metals to soil and plant tissues were studied. In the soil amended with the sludges the total N and extractable N and P contents increased, whereas the extractable K level remained nearly constant. Samples which had undergone a period of humification prior to sowing, mineralized part of their organic N and P during this period of time. Through sludge application, the levels of Cu, Zn, and Pb increased, the Fe content decreased while the extractability of Fe, Cu, Mn, Zn, and Pb increased as compared to the control. Sludge application enhanced the maize and barley yields as is the case of chicken manure. Sewage sludges supplied a considerable amount of available N to the plants, whereas the supply of available K was low. In the barley plants it was observed that the higher the yield, the higher the N and K contents, while in the maize crop this trend was only observed for K. Plants grown on soil amended with sludges absorbed a larger amount of Fe, Cu and Zn than those grown on the control soil. It was demonstrated that heavy metal absorption by the plants depended on the vegetal species.