Risk Of Soil Heavy Metal Pollution By Farm Manure Application And Phytoremediation Of Heavy Metal Polluted Soil

Along with the development of intensive livestock and poultry breadingproduction, large amount of heavy metal elements such as Cu, Zn was added to feedinorder to improve the feed efficiency, preventing from disease, speeding up the animalgrowth, and so on. Most of these heavy metals, however, were excreted to theenvironment through animal feces. Thus when the feces used as manure are applied tothe agricultural fields, there will be potential environment risk, In the present study,we analyzed soil heavy metal content in a farm after long-term application of theintensively managed farming pig manure. Through soil column simulation testmethod, we tested the migration and transformation of soil heavy metals after the useof pig manure in flooded conditions. Moreover, a field trial was conducted to studythe efficiency of phytoremediation with a heavy metal hyperaccumulator, Sedumalfredii Hance, affected by manure application. The main results are summarized asfollows:1、After the long-term application of pig manure, conditions of surface soil pH andorganic matter were remarkably improved. Soil N, P, K accumulation increased withlonger application of manure, especially significant in0-40cm soil depth Soilavailable N, P decreased, while K increased with soil depth. Heavy metal content insurface soil increased gradually with increasing length of manure application. Afterthe12-years of manure application, the contents of Zn and Cu in surface soilsachieved294mg/kg and66.6mg/kg respectively, higher than the state soilenvironment quality standard (GB15618-1995), the level2for soil Zn (<250mg/kg)and the level1for soil Cu (Cu <66mg/kg). Furthermore, with the long-termapplication of livestock manure in the soil, soil Zn activity was also increased. Znactivation rate increased from1.50%to15.39%, while the activation of Pb ratesdecreased down from33.7%to6.1%. It showed that the heavy metals from the pigmanure application were the important pathway for soil heavy metal pollution, andlong-term application of manure would result in some heavy metals accumulation inthe soil. 2、Results from soil column simulation experiment showed that, the application ofintensively managed farming pig manure significantly increased heavy metal contentin the surface soil. Manure application affected soil heavy metal activity andmigration, and the effect became more evident with increase of flooding time,especially on the effectiveness of the activation of soil heavy metals. Under conditionof9months flooding, influence of manure application on increasing soil available Zn,Cu and Pb went down beyond20cm soil depths. It showed that in the rice cultivationconditions (flooding), the long-term application of the heavy metal-containing manurewould cause the risk of heavy metal pollution to underground water.3、Analysis showed that the intensively managed farming pig manure containedgreatly higher amount of heavy metals of Zn and Cu than the organic farming pigmanure. In a field trial for remediation of heavy metals in soil by Sedum alfrediiHance, results showed that the application of organic farming pig manure as theorganic fertilizer improved heavy metal removal by the hyperaccumulator. Underdifferent fertilizer conditions, for zinc, the remediation efficiency order was as follows:OM (organic fertilizer)> OM+CF (cooperation of organic and inorganic fertilizers)>CF (inorganic fertilizer)> CK (control); and for Cd, the remediation efficiency orderwas as follows: OM> CK> OM+CF> CF. These results indicated that theapplication of organic farming pig manure is a good way to improve the efficiency ofsoil heavy metal remediation by Sedum alfredii Hance.