To discuss how placement influences the efficacy of zinc oxide and zinc sulfate fertilisers.

• Glasshouse experiments measured plant DM response and recovery of Zn fertilisers in oxide and sulfate form using three placement treatments - banded, mixed throughout the soil volume, and applied to the soil surface.
•  Also plant recovery of Zn from pure Zn phosphates and carbonates, which are likely reaction products of banded Zn fertilisers in soil, was measured. Recovery of Zn from Zn phosphates, carbonates and oxides was lower than that of Zn sulfates when banded.
• Placement was the major factor controlling plant responsiveness to Zn.
• Zinc oxide fertilisers had very low water solubility and slow dissolution rates in water, which is related to the high pH when the oxide is dissolved in water.
• There was significantly less recovery of fertiliser Zn by plants from Zn oxides than from Zn sulfates when the fertiliser was banded near the seed, likely due to higher pH in the band as the oxide dissolved.
• However, the Zn supply to plants was the same for both sources of Zn when fertilisers were mixed through the soil, as the soil likely buffered any dissolution-induced pH increases.
• This means that Zn oxides, despite their low water solubility, can be effective fertilisers if uniformly mixed throughout the crop rooting depth but Zn sulfate is preferable for banding or surface application.