Effects of Interaction between Nitrogen and Zinc on Forms of Zinc in Yellow- Brown Soil

Effects of interaction between nitrogen and zinc on forms of zinc in yellow- brown soil collected from a pasture in southern China were studied under pot- culture conditions. The results showed that pH of the soil was remarkably decreased with the increase rate of applied N- . Applied N had no effect on available zinc either with no zinc application or with low dose of applied N, but high level of N application obviously increased available zinc in the soil with zinc application. With increased rates of zinc application, the proportion of extractable (Ex- Zn), loosely organic matter bound zinc (LOM- Zn), manganese oxide- bound zinc (MnO- Zn), amorphously iron oxide- bound zinc (AFeO- Zn), tightly organic matter bound zinc (TOM- Zn) obviously increased and the proportion of crystalline iron oxide- bound zinc (CFeO- Zn), residual zinc (Res- Zn) in total zinc of the soil obviously decreased. With increased rates of nitrogen application, the proportion of Ex- Zn in total zinc of the soil significantly increased and so did for LOM- Zn. It was concluded that combined application of zinc and nitrogen had a synergism effect on Ex- Zn content and, therefore, increased the availability of soil zinc to plants. It may be suggested that the present experimental results be a guidance for wise fertilization in southern pastures.