| With the discharge of the three industrial wastes and the application of agro-chemicals in the agricultural ecosystem,accumulation of heavy metals in the soil is continuing,and threatening the environmental ecology and the safe production of agricultural products.The protection of ecological environment,remedy of soil heavy metal pollution and the safe production of agricultural products in heavy metal polluted farmland have been paid growing attention,which is also a challenge issue in China at present.Appropriate measures can be taken to reduce the bioavailability of heavy metals in soil and to maintain the ecological environment security,or to secure free from heavy metal pollution of agricultural products while without interfering agricultural production.Soil incubation experiments were adopted to study the effect of soil amendments on availabilities and transformation of heavy metals in the soils.The soil amendments used in present study were such as alkaline fertilizers(calcium- magnesium phosphate fertilizer,silicon - calcium - potassium-magnesium fertilizer),inorganic compound(calcium carbonate),biochar,and organic-inorganic compound fertilizer.The main results are as follows:(1)In Cd polluted farmland soil,the effects of different materials on soil organic matter content and pH were different and changed with incubation time.Fertilizers and biochar increased soil organic matter content,and silicon - calcium - potassium-magnesium fertilizer and calcium - magnesium-phosphate fertilizer increased soil pH and maintained it for a long time(120 d).(2)All the materials used significantly reduced the soil Cd availability.At the same dosage(1%),after 60-120 days,concentration of available Cd in the soil treated with fertilizer and biochar was significantly lower than that of the control.At day 90,treated withwood charcoal,soil Cd availability decreased by 56.72% compared with the control.At day 120,the available Cd concentration in each treatment decreased significantly,ranging from 8.22% to 50.68% compared with the control.Fractionation analysis showed that the change of soil Cd availability was closely related to its form transformation,and the application of amendments increased the proportion of residual Cd fraction.(3)In the mining soil,different materials and their different proportions had different effects on the availability of different heavy metals.Soil Cd availability was greatly decreased by the combination of peat and organic-inorganic compound fertilizer.The persistent effect(60 days)and passivation effect were the best under the combined application of peat(1%)and 4-5-6 organic-inorganic compound fertilizer(0.20%),reaching passivation efficiency of 23.20%.Single application of organic-inorganic compound fertilizer(0.20%)had the greatest effect on reducing soil available Pb,and its passivation efficiency reached 11.22% in 60 days.Zn availability in all the materials treated soils was significantly reduced.The combination of peat(1%,5%)and organic-inorganic compound fertilizer(0.20%)showed the greatest effectiveness in decreasing soil Zn availability during 30-60 days,and the passivation rates reached 41.37% and 40.92%,respectively.In general,soil Cd,Pb and Zn availabilities could be simultaneously reduced by joint application of 1% peat and 0.2% organic-inorganic compound fertilizer,or 1% calcium carbonate,1% peat and 0.2% organic-inorganic compound fertilizer.These two combinations could be used as candidate materials for vegetation restoration in Cd,Pb and Zn complex polluted soil.Therefore,we should not only emphasize the difference of passivation effect of soil amendments on soil heavy metals,but also need to consider the influence of time factor after their applying to the soil to control soil heavy pollution. |
