| Agricultural use of municipal sewage sludge has provided a novel solution for the treatment and recycling of municipal sludge. Given that large amount of municipal sewage sludge wastes are produced in China, it would be economic and efficient to utilize the municipal sewage sludge for improving soil fertility. Nevertheless, not enough attention has been received to this research area so far. In general, plough layer is characterized with optimal physio-chemical properties, as well as good fertility. A top layer of 1 cm thick requires thousands years of development from the deep soil to which root system of plants might extend. The common features of subsoil are the lack of nutrition and oxygen with unfavorable air and water permeability, even though this layer could often be reached by most plant roots for the purpose of water and nutrients. Therefore, aside from the topsoil, the improvement of subsoil should be given equal attention to improve the growth and extension of root system of plant, thus to ensure nutrient supply for the aboveground part of plants and high-yield.Five different treatments were prepared in this study, with sludge addition in subsoil at ratios of 0%,2.5%,5%,7.5% and 10%. The research mainly consisted of the following aspects:1. The varying patterns in the content of water soluble elements were investigated in the course of subsoil improvement as affected by municipal sludge, in order to estimate the environmental influence of sludge on groundwater; 2. The changing patterns of major nutrients and heavy metals during deep soil improvement were studied to evaluate the effect of municipal sludge on subsoil fertility, as well as on the activity of heavy metals in subsoil; 3. The growth and production of plants, together with content of heavy metals, were determined to analyze the effects of sludge amendment on yield increasing and food security. Meanwhile, the optimal ratio of sludge to soil was obtained. The results were shown as follows:1. The application of municipal sludge significantly increased the content of soluble nitrate in deep soil, which increased the risk of nitrogen pollution in water environment. Special care should be taken to the eluviation of nitrate in the process of sludge utilization. Soil pH was decreased to a certain extent, suggesting that the sludge might be additional advantage to the improvement of alkali soil..The selection of sludge ratio should be dependent on the pH value of the soil.2. Since the sludge was short of potassium element, there was no significant change in the content of potassium in subsoil, but remarkable increase in elements of nitrogen and phosphorus was observed. It was strongly recommended to utilize the sludge accompanied with potassium fertilizer. In the experiment, the heavy metal contents remained under the limit of the Secondary soil environmental quality standards for heavy metals with the addition of sludge. However, there was potential risk induced by the heavy metal accumulation after years of application. Therefore, the effects of municipal sludge application should be carefully monitored and not to exceed the recommended time limit.,3. The overdose of sludge was found to inhibit the accumulation and absorption of nutrients for the plants. Furthermore, the excessive sludge addition resulted in high content of nitrate in plant leaves. Taking into account the production and food security, the optimal ratio of sludge appeared to be 5% in the present experiment. |
PDF Full Text Request