| Animal manures of intensive livestock and poultry farms are composed of complex materials. Effect of continuous application of chicken manure (CM) and pigeon manure (PM) for six crops on soil nutrients and heavy metals was investigated in a vegetable soil in Guangzhou, south China. Application rates (N 0～450 kg·ha-1) of CM and PM were calculated considering their N contents. The results indicate that concentrations of soil ammonium N, nitrate N and phosphorous extracted with sodium bicarbonate (P-NaHCO3), potassium extracted with ammonium acetate (K-C2H3O2NH4) increase considerably after continuous application of CM and PM for three crops. Moreover, their concentration increments go up with the rates of CM and PM. Concentrations of soil nitrate N and K-C2H3O2NH4 after the sixth crop reduce compared with those after the third crop, and also decrease compared with their original ones due to the heavy rainfall during the three latter crops. However, concentrations of soil ammonium N and P-NaHCO3 are still higher than their original ones, and their concentration increments increase with the rates of CM and PM, respectively. Two manures contain low Pb, Cd, Cr and pigeon manure contains low As, there is no great influence on soil Pb, Cd, Cr and As by continuous application. Two manures contain higher Zn (172.0 and 299.8 mg·kg-1, respectively), leading to soil Zn concentration increments from 0.7 to 17.1 mg·kg-1 after the sixth crop. Meanwhile, CM has relatively high Cu (117.7 mg·kg-1) and As (39.6 mg·kg-1), indicating the trend to accumulate Cu and Zn in soil after the sixth crop. |
