Abstract: Based on the long-term location experiments, the chemical characteristics of zinc under the condition of 17 years' continuous application of zinc fertilizer were studied by using a sequential extraction technique. The results showed that zinc has accumulated in soils after continuous application of zinc fertilizer for 17 years. The total and DTPA extractable zinc in 0-60 cm soil were higher in zinc treated soil than that in the control. In addition, after long-term application of zinc fertilizer, zinc has accumulated in surface soil and transported to deep soil. In soil zinc fractions, mineral bonded zinc accounts for 95.57%-99.11% of total zinc and organic matter loosely bonded zinc accounts for 0.82%-3.58% of total zinc. Zinc fractions studied in the experiments all increased in zinc fertilizer treatment compared with the control. The result also suggested that most zinc added to soils has entered into soil minerals and little has entered into soil solutions or combined with soil organic matter, carbonate or manganese oxides. The correlation and principle component analysis suggested that the exchangeable zinc, the organic matter loosely bonded zinc and the carbonate bonded zinc could indicate the availability zinc in soils, respectively. Long-term application of zinc fertilizer also improved the nutrient condition of wheat, which accelerated the absorption of zinc by wheat. The zinc contents and uptake amounts in each organ of winter wheat was higher in zinc treatment than that in the control.

Key words: Loess plateau, Continuous application, Zinc fertilizer, Soil zinc fraction, Soil zinc availability