Effects of artificial apple orchard planting ages on soil heavy metals distribution

The paper studied the effect of different planting ages of apple orchards on distribution of soil heavy metal in order to lay the theoretical foundation for the high quality of apple production in the Weibei Highland.Numerous studies focused on the spatial distribution of soil heavy metal of specific aged vegetable greenhouse.However,few studies were done for different artificial planting ages of apple orchards.In this paper,the principle and methods of geo-statistics(SPSS)were used to investigate the content of soil heavy metal at three soil depths(0-20 cm,20-40 cm,and 40-60 cm) of different aged apple trees(0,20,40,and 60 years) at the arid Weibei Highland in the Loess Plateau,Luochuan County,Shaanxi Province,China.The results showed that high input and different apple tree ages have an obviously effect on soil heavy metal content and its migration.Soil As content change presents reducing tendency(4.1→0.4 mg/kg)on the different soil layers along with the tree age increases(0→60 years).Soil Cr content is higher in 40-year apple orchard at the different soil layers(87.3,89.7 and 94.6 mg/kg,respectively),but is lower in 60-year apple orchard at the different soil layers(76.0,79.5 and 73.3 mg/kg,respectively).As to 0-20 cm,the soil Cu and Ni contents increase progressively along with the tree age growing in a line(22.9→31.7 mg/kg and 29.6→31.9 mg/kg).Soil Pb content of apple orchards of different planting ages all reduces along with the soil layer increases.The change of soil Zn content of apple orchard of different planting ages has no obvious rule in different soil layer.But the synthetic pollution indices of soil heavy metals of all soil samples were below 1,the soil environment quality of artificial orchard of 0,20,40 and 60 years in Luochuan was good,reaching the clean level.The apple orchards of Luochuan are in accordance with the demand of the pollution-free apple production by the national environment quality standard for soils.