Status of heavy metals in vegetable soils under different patterns of land use

【Objectives】 A national vegetable soil survey on total heavy metal concentrations under three patterns of land use (greenhouses with wall or without wall, open field) was evaluated to provide a scientific basis for vegetable soil quality improvement, and high-efficiency and safe fertilizer recommendation. 【Methods】 More than five hundreds of representative soil samples at depth of 0-20 cm were collected from the main vegetable production regions in China (Northeastern, Huanghuaihai, Northwestern, Southwestern, Central China, East China, and South China) located in rural areas away from suburbs of their cities, and not affected by the waste air, water and residue from industry and the tail gases emitted by automobiles etc. The sampling periods comprised after harvest, prior to fertilization, or at late stage of growth in 2013,and the total heavy metal concentrations under the three patterns of land use were investigated in this study. 【Results】 1) The total Cu, Zn and Cd concentrations in the vegetable soils inside the greenhouses (with wall and without wall) are significantly higher than those in open vegetable soils, with average increases of 12.2%, 21.7% and 30.4%, respectively. 2) The total Cu, Zn and Cd concentrations in the vegetable soils are significantly increased with the elongation of vegetable production history. Co-contamination of several heavy metals often might occur synchronously in the vegetable soils underdifferent land use patterns. Significant correlation relationships exist between soil heavy metals (Cu, Zn, Cd, etc.). 3) The total Cd concentrations in 19.2%-22.3% of soil samples under different land use patterns are beyond the 2nd criterion according to the Soil Environmental Quality Standard for Vegetable Fields (GB15618-2008), and Cd pollution indices of the vegetable soils for greenhouse with wall, the vegetable soils for greenhouse without wall, and the open vegetable soils are 0.97, 0.98 and 0.70 respectively. In 0-14.6% of soil samples, the total Cu, Zn, Pb, Cr, As and Hg concentrations are beyond the 2nd criterion according to the Soil Environmental Quality Standard for Vegetable Fields, and the single-factor pollution indies of soil heavy metals are in the range from 0.06 to 0.52. 【Conclusions】 There are significant higher accumulations of soil Cu, Zn and Cd for the greenhouse vegetable field compared with the open vegetable field in this study, which is probably caused by the corresponding higher application rates of chemical fertilizers and organic manures, especially organic manures. The vegetable soils for greenhouses with wall and greenhouses without wall in sampling areas are at the warning level of Cd pollution, and the soils from the open vegetable fields are not generally contaminated with Cd. All the vegetable soils from different land use patterns are not in danger of contamination of Cu, Zn, Pb, Cr, As and Hg.