ZINC-DEFICIENCY IN WHEAT AND LUPINS IN WESTERN-AUSTRALIA IS AFFECTED BY THE SOURCE OF PHOSPHATE FERTILIZER

A long-term field experiment is being conducted in the wheatbelt of Western Australia to determine the effects of source of phosphate fertiliser on the residual effectiveness of zinc (Zn) to wheat and to sweet, narrow-leafed lupins grown in rotation. The initial 2 years' results of that experiment reported here indicate that both wheat and lupins responded to the addition of Zn to the soil. The requirements of these crops for Zn, can be mostly met with the small amount of Zn that is a natural component in single superphosphate manufactured from rock phosphates, but not with diammonium phosphate (DAP). The internal requirements for Zn of the aboveground tissues of lupins appear greater than those of wheat. Depending on the stage of growth, critical concentrations of Zn in the youngest leaf tissues of wheat that were prognostic of Zn deficiency, were found to vary from about 7 to 16-mu-g/g, while those in lupins were found to vary from about 28 to 37-mu-g/g.