THE MECHANISM OF PHOSPHORUS-INDUCED ZINC DEFICIENCY IN BEAN (Phaseolus vulgaris L.)

Abstract

The nature of the P-induced Zn deficiency in bean plants was studied in a growth chamber experiment using three pedogenically different soils. Application of P (0, 40, 80 and 160 mg P kg−1 soil) resulted in significant dry matter (DM) yield increases. Maximum DM yields were attained at the 40 mg P kg−1 application rate. Application of Zn (0, 5 or 10 mg Zn kg−1 soil) without P application had no effect on DM yields of bean plants. However, Zn application in combination with P application resulted in significant DM yield responses. There was no evidence that the P-induced Zn deficiency was a result of differences in soil characteristics or influence of P on the water soluble plus exchangeable, organically bound, Mn- and Fe-oxide bound or residual Zn fractions. The Zn concentration in bean plant tops was significantly reduced due to P application and the magnitude of the reduction was greatest with the first increment of applied P (40 mg P kg−1 soil). Application of P induced Zn deficiency, at least partly, by stimulation of growth and subsequent dilution of tissue Zn concentration. Translocation of Zn from roots to tops appeared to be restricted at 80 and 160 mg applied P kg−1 soil treatments, as evidenced by the reduction of Zn uptake in non-Zn treatments. Thus, plant dilution effects and reduced translocation of Zn from roots to tops were the two mechanisms responsible for the observed P-induced Zn deficiency in this study. Key words: P × Zn interaction, plant availability, plant uptake, soil Zn fractions, soil P, Zinc-65