Distribution Of Zinc Species In Vegetable-planting Soils Of Chengdu And Its Affecting Factors

Zinc is an essential trace element for organisms with important environmental and physiological significance.The chemical behavior and bioavailability of zinc depend on its speciation in soil,the species of zinc in soils are controlled by general soil characteristics and other factors.However, there are few researches concerning the distribution of zinc species and its affecting factors,let alone soil zone and layer depth in vegetable-planting soils.In this paper,we focus on zinc speciation in planting vegetable soils of Chengdu,the contents and distribution of total zinc,zinc species as well as corresponding physico-chemical properties in each soil zone and layer were systematically investigated.Besides,the relationships between total zinc,zinc species and physico-chemical parameters were investigated and assessed by calculating Pearson correlation factors.Some conclusions are as follows:(1) A low-cost procedure was developed for the total zinc digestion and zinc speciation analysis with good accuracy and practicability.(2) In vegetable-planting soils of Chengdu,there are no obvious pH difference between surface arable layer and sub-surface non-arable layer,comparing with other zones,pH values of Chenghua zone and Jinjiang zone are apparently lower;the contents of organic matter in arable layer are higher than that in non-arable layer;total sulfur in arable layer and non-arable layer have significant differences in content,the content of total sulfur in surface arable layer is higher than that of sub-surface non-arable layer;the iron content of Fe/Mn oxyhydroxide??s significantly higher than manganese content.(3) The content of total zinc in Chengdu vegetable soil using AAS is 89.48~158.52mg/kg,which conforms to the secondary standard (pH<6.5, zinc≤ 200mg/kg) in the national reference norms (environmental quality for soils,GB15618- 1995).It is concluded that vegetable-planting soils of Chengdu have not been polluted; and total zinc in surface arable layer and in sub-surface non-arable layer were significantly different.(4) In the vegetable soil of Chengdu, the distribution of zinc speciation is as follows: residual Zn>organic-bound Zn>iron-manganese oxide bound Zn>exchangeable Zn > acid rain Zn.There were a very small proportion of zinc speciation which can easily be leached by acid rain, the proportion of exchangeable zinc which can be easily absorbed by plants is 5.20%,this zinc speciation can promote or affect growth and development of plants. In Chenghua and Jinjiang areas which were seriously affected by industry and population,exchangeable Zn,especially the percentage of acid rain Zn was significantly higher than other areas,while residual zinc was obviously lower than other areas.(5) In surface arable layer and sub-surface non-arable layer soil,exchangeable Zn has a significantly negative relationship with pH and CEC;iron-manganese oxide bound zinc and iron content were positively correlated;residual zinc and exchangeable zinc showed significantly negative correlation.In arable layer soil,acid rain Zn has a significantly negative relationship with pH and significantly positive relationship with iron content of Fe/Mn oxyhydroxides,residual zinc has a positive relationship with pH value and significantly negative relationship with acid rain zinc. In non-arable layer, organic-bound zinc has a positive relationship with iron content.