Effect Of Sludge Compost On Soil-plant Systems Of Chongqing

Sewage sludge contained lots of organic matter,nitrogen,phosphorus and other plant nutrient elements.As a result,that can be used to modify the soil and impove the plant growth.The agricultural application has become one of the most important ways for sewage sludge recycling. Otherwise,there were also a certain heavy metals in sewage sludge.It might lead to the accumulation of heavy metals in soils,if under long-time application.The effects of agricultural application on soil-plant ecosystem varied with soil type,plant types and climatic conditions.In order to investigate the effect of agricultural application of sewage sludge compost on soil-plant ecosystem and seek their optimal amounts and ways,the pot experiments were carried out using the Lactuca sativa as tested plant.And in the current study two kinds of soils,Xanthi-Udic Ferralosols (XUF)and Purpli-Udic Cambosols(TPUC)were employed,which were widely used for cultivation in Chongqing.Meanwhile,the effect of agricultural application of sewage sludge compost on the soil N-supplying capacity was also studied through incubation test.The results as follows:1.The yield and quality of Lactuca sativa were both improved by the application of sewage sludge compost.In general,the treatment of sludge compost combined with chemical fertilizers took full advange of the inorganic fertilizer and organic nutrient.As a result,that greately improved the plant growth and reached the same yield and quality as only treated with chemical fertilizer. Moreover,it also efficiently improved the physicochemical properties of soils.2.The content of N,P and K significantly increased in Lactuca sativaand after application of sewage sludge compost,as well as total N,total P,total K,available N,available P,available K and organic matter in soils.3.The total and available Cu,Zn,Pb and Cd in soils significantly increased after application of sewage sludge compost.Furthermore,the heavy metals in plant were greately correlated with those in sewage sludge compost and increased with the amount of application increasing.Therefore,it is necessary to control the environmental risk of heavy metals in agricultural application of sewage sludge compost.4.The content of heavy metals significantly increased in aboveground of Lactuca sativa after the application of sludge compost,compared to the control.And the Pb content in edible parts exceeded the limitation of national criterion(GB18406.1-2001)in all treatments.On the other hand, the contents of Cu,Zn and Cd were all within the scope of criterion with the low application of sludge compost.When the application amount of sludge compost was less than 369 g/kg,the heavy metals contents in Lactuca sativa were all lower than the limitation(except for Pb).Thus,it is necessary to develop the methods for stabilization of heavy metals in soils when sewage sludge compost was utilized,such as the lime treatment.In addition,in order to reduce the harm caused by heavy metals accumulation to the largeset extent,it should avoid planting leaf vegetables and the plant whose roots were collected.5.The effect of nitrogen fertilizer application depended on soil nitrogen supply capacity.And the soil nitrogen mineralization was one of the important factors to impact the ability of soil nitrogen supply.Temperature and moisture of soils were the major environmental factors impacting the mineralization of soil organic nitrogen.The mineralized nitrogen in XUF increased by 2.3 to 6.8 times compared to the control after sludge compost application,while that in TPUC increased by 1.9 to 13.1 times.6.The time,temperature and moisture at the peak values of mineral nitrogen were greatly impacted by the sludge compost application.The maximum mineralized nitrogen in XUF occured at 25℃and 70%in early stage of culture,while at 35℃and 50%in the same stage after sludge compost application.On the other hand,that in TPUC occurred at 35℃and 90%in early stage, while at 15℃and 90%in late stage after sludge compost application.