Many industrial by-products containing Zn are being processed and sold as Zn fertilizers. Some baghouse dusts and flue dusts which contain ZnO may be used as fertilizers or may be partially acidulated with H2SO4 to form Zn oxysulfates (various mixtures of ZnO and ZnSO4). Spent H2SO4 by-products of several industries, especially the galvanizing industry, also may be processed into ZnSO4 fertilizers. The level of water-soluble Zn (as a percentage of total Zn) in these fertilizers is mainly related to the relative contents of ZnSO4 (water soluble) and ZnO (water insoluble). Other published results have shown that availability to plants of most nutrients in a granular fertilizer is related to their water solubility.
Response of corn (Zea mays L.) to fine and granular Zn fertilizers varying in level of water-soluble Zn was determined on a limed Zn-deficient Crowley silt loam (Typic Albaqualf) in three greenhouse pot experiments. Dry matter production and Zn uptake by corn were similar with several finely ground (<0.15 mm) Zn fertilizers varying from 0 to 100% of their total Zn in water-soluble form.
Crop response to granular (1.7 to 2.4 mm, ×8 + 12 mesh) Zn fertilizers increased with level of water-soluble Zn in several ZnSO4 fertilizers made from spent acids, Zn oxysulfates, and ZnO by-product fertilizers. Corn dry matter production and Zn uptake were significantly lower with fertilizers containing <40% water-soluble Zn. Crop response to granular mixtures varying in proportion of reagent grade ZnSO4 and ZnO gave similar results in two experiments. These results show that at least 40% of the total Zn in granular Zn fertilizers should be in water-soluble form to be fully effective for crops.