| One hundred and two surface soil samples were collected from four fields in a farm in Daxing district of Beijing, and analyzed for concentration of Cu, Zn, Pb, Cr and Cd. Soil pH, OM, the concentration of Fe and Mn was also analyzed. The results of statistical analysis indicated there was no significant difference among three wheat fields, but the difference between wheat field and vegetable field was evident. In the wheat fields, the concentration of heavy metals in soil was all below the critical value of first level in environmental quality standard for soils. On the contrary, the concentration of Cd in some plots of vegetable field exceeded the critical value of second first level in environmental quality standard for soils. Principal component analysis was applied to estimate the sources of heavy metals. The results grouped Cu, Cd, and Zn in factor 1, Cr in factor 2, Pb in factor 3. Semivariogram of factors in the whole farm was fitted well by Gausssian model. Further analysis showed good spatial correlation of factor 1, and poor spatial correlation of factor 2 and factor 3. The approach of ordinary kriging interpolation approved the Cu, Cd, Zn in the soil was associated with the agricultural landuse. The distribution of heavy metals was mainly attributed to the excessive input of fertilizer and pesticide in vegetable product practice. |
