[Accumulation and Migration Characteristics in Soil Profiles and Bioavailability of Heavy Metals from Livestock Manure].

The long term and high dosage application of livestock manure may result in heavy metal accumulation and migration in the soil, which may endanger food security and affect the top soil heavy metal environmental capacity. Thus, one of the most important tasks for prevention of soil heavy metal pollution is scientific determination of the safe use load of heavy metals in livestock manure. A 4-year field plot experiment was carried out to quantitatively study the accumulation and migration characteristics of heavy metals from pig and chicken manure in soil profiles and the differences of bioavailability. The results showed that the contents of Cu and Cd increased significantly by 43.8%-118.6% and 28.2%-44.9% in topsoil(0-15 cm) after 4-consecutive year application of pig manure, and the contents of Cu, Zn, Cd, Cr, As, Pb also increased by 29.7%-48.5%, 239%-456%, 19.9%-80.8%, 40.4%-163%,11.8%-22.0% and 80.3%~95.0% obviously after application of chicken manure. The accumulation rates of Cu and Zn in topsoil were 76.4%-119% and 14.2%-20.4% with pig manure, 72.1%-88.7% and 63.9%-78.9% with chicken manure. Under a high dosage of pig and chicken manure, Cu and Zn migrated to a deeper soil evidently. Applying 60 t·hm of pig manure after 4-consecutive year, Cu could migrate to 15-30 cm soil layer, Zn migrated to 30-60 cm soil layer with chicken manure. Except topsoil, the contents of Cr, Cd, As, Pb did not significantly increase in other soil layers. 4-year continuous application of chicken manure significantly decreased the contents of Cu and Cd, but increased the contents of Zn and Cr in wheat grain and the content of Zn in wheat straw. Pig manure significantly decreased the content of Zn in wheat grain, but increased As content with 60 t·hm, the contents of Cu and As in wheat straw also increased significantly. Besides, the cumulative rate of heavy metals in wheat was no more than 6%, wheat grain carried out more Cu, Zn than straw, but the Cd, Cr, As, Pb were opposite. The cumulative rate of heavy metals in wheat decreased with the increasing application of manure. This research has an important significance in scientific determination of the heavy metal loads of plow layer, ensuring the quality and safety of agricultural production, and providing a scientific basis for the source control of soil heavy metal pollution and the safety production of agricultural goods.