Study On Effect Of Sludge Compost Application On Soil-Plant Ecosystems

By studying on the equilibrium and transfer of nitrogen, phosphorus in soil-plant ecosystem, and their environmental effects, this paper aims at finding the optimal application rate of sludge compost to green area, which may supply theory and practical guide for the garden utilization of sewage sludge.This research investigated the performance of potted experiment and leaching experiment of Tall Fescue and Tagetes Patula using the dewatered sewage sludge that has about 80% water content from Shanghai Quyang Water Quality Purifying Factory. The mix rates of the Shanghai local and tidal bank soils with the quick compost sludge were 0%, 5%, 10% and 20%.The main experimental results and conclusions can be summarized as follows:The potted experiment demonstrated that there exists dose-effect relationship between sludge compost application rate and growth response of plants. Due to poor nutrition in tidal bank soils, the plants could not grow well. With 5%~10% sludge compost added, burgeon increased and plant's growth was quite good. However, when sludge addition increased to 20%, burgeon decreased (even no germination) because of the inhibiting effect. Thus, 20% was recommended as the maximum application rate and the optimal application rate was 5-10% when applying the sludge compost. It could also found that sludge compost showed stronger inhibiting effect towards flower plant than herbaceous plant during plant cultivation.N and P are abundant in sludge compost but poor in tidal bank soils. Adding sludge compost to tidal bank soils could increase fecundity of soil. The results of potted experiment which studied on the equilibrium and transfer of nitrogen in soil-plant ecosystem suggested that ammonia nitrogen transferred by organic nitrogen and ammonia nitrogen in the mixed soil, half of which was absorbed by plants, the remain rapidly transferred to nitrate nitrogen, so that ammonia nitrogen decreased to a lower concentration in a short time. Some nitrate nitrogen was absorbed by plants, the most lost as gaseous nitrogen by denitrification. It was concluded from the transfer ofnitrogen that there is no environmental pollution for the garden utilization of sewage sludge because that inorganic available nitrogen in the mixed soil was mainly absorbed and lost as gaseous nitrogen.It was also found in the equilibrium and transfer of phosphorus in soil-plant ecosystem that easy activating inorganic phosphate was fixed as biologic phosphorus temporarily. With the metabolism of microorganism, biologic phosphorus was given off again and transferred to available phosphorus by mineralization. Meanwhile, affected by microorganism and enzyme in soil, part of organic phosphorus in mixed soil was gradually transferred to available phosphorus. In a word, the available phosphorus in the mixed soil could meet the requirement for plant growth.The results from leaching experiment showed that total nitrogen, total phosphorous and rapidly available phosphorus migrated to the lever of 0-5cm after leaching in 10% mixed soil, while ammonia nitrogen remained at its place and nitrate nitrogen migrated to the level of (MOcm. the concentration of nitrate nitrogen as well as ammonia nitrogen, total phosphorus and heavy metals in the leaching was under the III class of the quality standard for surface water and the IV class of the quality standard for ground water. It was analyzed that tidal bank soils with 10% sludge compost addition will not polluted the environment.Balance analysis of soil-plant ecosystem in leaching experiment after application of sludge compost showed that N and P in mixed soil vary little after leaching. In the mixed soil, gaseous nitrogen has the highest loss effect, followed by nitrogen absorbed by plants, the leaching nitrogen has the least effect, the result of which is also fit for phosphorous. The nitrogen in watering contributed to plant absorb, while impact of phosphorus could be neglected.The paper analyzed the positive and negative effect of garden virescence taking nitrogen, phosphorus, heavy metals into consideration. It could be concluded from effect balance that the optimal application rate of sludge compost is 5-10% for garden virescence.