Transformation and distribution of forms of zinc in acid, neutral and calcareous soils of China

Abstract

The distribution of native zinc in 18 soils of China and the redistribution and transformations of added soluble zinc in 3 representive soils (acid, neutral and calcareous) were studied. Native Zn in 18 soils of China was mainly distributed over the residual fraction (60–99%) and the crystalline iron oxide fraction (5–30%). The percentages of the residual and exchangeable fractions were higher and the iron oxide fraction lower in acid soils than in calcareous soils. Soil pH is the most important factor of controlling the distribution of native and added Zn in soils. Zinc enrichment in the iron oxide fraction increased exponentially with increasing soil pH. The redistribution of added Zn in acid, neutral and calcareous soils occurred in the residual fraction, followed by the crystalline iron oxide fraction and the weakly bound to organic matter fraction at the lower loading level; and most of the zinc in the residual fraction and the weakly bound to organic matter fraction at the higher loading level of Zn. Zn in the amorphous iron oxide and crystalline iron oxide fractions was much higher in calcareous soils where Zn was added than in acid and neutral soils. Zn in the exchangeable, the weakly bound to organic matter, and to some extent, the carbonate fractions increased with increasing the treatment level of Zn. Transformations of the added Zn from the exchangeable, the weakly bound to organic matter and the amorphous iron oxide fractions into the strongly bound to organic matter and the crystalline iron oxide fractions were observed in soils. Much more complete transformations of these fractions occurred in calcareous soils than in acid and neutral soils. These transformations from the more active and available fractions into the more stable and less available fractions are important in controlling the availability and toxicity of Zn in soils to plants.