Effects of Zn sources and application methods on the contents of various Zn fractions and Zn fertilizer utilization efficiency

【Objectives】Proper sources and application methods of Zn can improve grain Zn nutritional quality and Zn utilization efficiency. Therefore, the effect of two Zn fertilizers and two application methods on Zn fractions and Zn use efficiency were investigated in potentially Zn-deficient calcareous soil.【Methods】 A greenhouse pot experiment with two Zn sources(Zn-EDTA and ZnSO4·7H2O)and two application methods(mixed with whole soil in a pot, and top dressed in 3 cm wide banding below wheat)experiment was conducted. The contents of five different Zn fractions were analyzed, and the Zn fertilizer efficiency of wheat was calculated.【Results】 Both Zn-EDTA and ZnSO4·7H2O increased the grain and straw Zn concentration. The grain Zn concentration was increased by 43% in the mixed ZnSO4·7H2O application, and by 57% and 75% in the mixed and banded Zn-EDTA applications, respectively. The Zn utilization efficiency was 6.5% and 5.3% in the mixed and banded Zn-EDTA applications, 3.6% and 1.3% in the mixed and banded ZnSO4·7H2O applications. After harvest, the soil available Zn were 9.25 mg/kg and 1.97 mg/kg with banded application of Zn-EDTA and ZnSO4·7H2O, which were 2 and 1.8 times of those with the mixed applications. Both ZnSO4·7H2O and Zn-EDTA increased the contents of all the five Zn fractions, which were all in the order of loose organic matter Zn(LOM-Zn) carbonate bonded Zn(Carb-Zn) tight organic matter bound Zn(TOM-Zn) manganese oxide bound Zn(OxMn-Zn) exchangeable Zn(Ex-Zn). The exchangeable Zn concentration of the mixed ZnSO4 and Zn-EDTA applications were 0.12 and 0.13 mg/kg, respectively. The LOM-Zn concentration of banded ZnSO4·7H2O and Zn-EDTA applications were respectively 5.26 and 1.56 mg/kg. The trends for carbonate-Zn and loose organic matter-Zn concentrations in the mixed and banded ZnSO4·7H2O applications were similar. Manganese oxide bound Zn concentration with the banded Zn application was 4 times of that in the control. The soil available Zn concentrations were positively correlated with the Ex-Zn, LOM-Zn and Carb-Zn concentrations. Compared to no Zn application, the concentrations of LOM-Zn and Carb-Zn were significantly increased, while that of TOM-Zn was decreased with the application of Zn-EDTA. 【Conclusions】 In the potentially Zn-deficient calcareous soil, the application of Zn-EDTA could increase the contents of potentially available Zn and the Zn utilization efficiency, and there was higher available Zn concentration to sustain plant available Zn until wheat harvest after the application of chelating Zn fertilizer. Thus, it increased Zn utilization efficiency. The banded application treatments produced the higher available Zn fractions near the wheat roots than the mixed application treatments. Key words: calcareous soil; Zn fertilizer; Zn fertilizer application methods; Zn fractions; Zn fertilizer utilization efficiency; wheat