Heavy Metals Pollution And Their Control In Garden Red Soil Received Intensive Farming Livestock Manures

The poultry manures from intensive farming often contain high contents of heavy metals just as copper, zinc, lead, cadmium and so on, and these manures are widely used to vegetable field at a high rate. After a long-term application of such these manures, it will cause accumulation of Cu, Zn, Pb and Cd in soil and crops, which affects the growth of crop, heavy metal uptake and groundwater quality. This study surveyed animal feed, poultry manures, soils and vegetables sampled at 39 different sites in the Yujiang city in Jiangsu province, China, where manures are applied for many years. A series of experiments and pot trials were designed to investigate the transferring processes of Cu and Zn from manures to water and plants.The main results were as follows.Firstly, this study investigated the concentrations of Cu, Zn, Pb and Cd in feeds, pig manures, soils and vegetables sampled from 39 intensive farming plants in Yujiang County, Jiangxi Province. The results showed that the rate of exceeding allowable limit of Cu in big pig feed and piglet feed were 81.6% and 30.8%, respectively. Meanwhile, the rate of exceeding allowable limit of Zn in big pig feed and piglet feed were 89.5% and 94.9%, respectively. In addition, Cu and Zn concentrations in some pig manures were also above the Pollutant Emission Standard for Livestock and Breeding Industry (In China). Furthermore, there were significant positive correlations between the heavy metal concentrations in feeds and pig manures. Total Zn concentration in 7.8% of soil samples and total Cd concentration in 5.2% of soil samples exceeded the Chinese Soil Environmental Quality Standard III, which means they have been heavily polluted. The survey also showed that the concentrations of Cu, Zn, and Pb in all vegetable samples were lower than the National Food Hygiene Standard, while Cd concentrations in Ipomoea Aquatica and Colocasia Esculenta exceeded the standard. The significant positive correlations were found between the total Cu, Zn, Cd concentrations and the extractable heavy metal concentrations in soils.Secondly, a pot experiment was designed to study the effect of 0, 2%, 4% of pig manure addition on heavy metal uptake by vegetables Cu and Zn. We chose three kinds of soil amendment (attapulgite, limestone, fertilizer of calcium magnesium phosphates) on manure contaminated soil improvement .The results showed that significant improvement of soil pH was been found in pig manure additive treatment. Pig manures obviously increased soil electrical conductivity, and promoted plant's growth. Vegetables absorb Cu, Zn addition of the quantity and proportion of pig manure. Modifier can inhibit the bioavailability of heavy metals in soil, in which the strongest inhibitory effect of lime, and lime have a fixed role of red phosphorus.Thirdly, soil column leaching experiments had studied the dynamic changes of soil pH, contents of EC, DOC, available phosphorous and heavy metals during the leaching process. The results showed that applications of pig manures can increase soil pH, EC and organic mater contents, meanwhile, pig manures brought some heavy metals just as Cu and Zn into soils. These dissolved Cu and Zn may be leached into groundwater, thereby endangering human health. Modifier hydrated lime can improve soil fertilizer while not lead to heavy metal pollutions. Our research shows that hydrated lime can better improve the acid soil pH, and to limit the activity of Cu, Zn and other heavy metal ions, it can effectively reducing the risk of migration of heavy metals in groundwater.