Influence of water solubility of granular zinc fertilizers on plant uptakeand growth

Zinc (Zn) fertilizer application has increased during the past three decade s. This:increase has created the need for more information regarding the av ailability and agronomic effectiveness of Zn containing fertilizers because differences,of opinions exist relating the relationships between Zn water solubility and plant availability. Plant availability of eight commercializ ed Zn fertilizer materials having different water solubilities was measured under greenhouse conditions. Corn (Zea mays L.) plants were grown for 40 d ays in a soil(loamy, mixed, mesic arenic Ustollic Haplargid) amended with l ime to two pH's: 6.3 and 7.4. To evaluate the effect of pH, some Zn fertili zers were used at both:soil pH levels while all Zn fertilizers were used in the pH 7.4,soil. The experimental design was a factorial combination of pH , Zn fertilizers, and Zn rates of 0, 2.1, 4.2, 8.4 mg Zn kg(-1) soil. Dry m atter production and Zn uptake increased significantly when the soil pH dec reased from 7.4 to 6.3. The highest dry matter production was obtained with ZnSO4 (ZnSO4. H2O, 99.9% total water soluble Zn), Zn20 (Zn oxysulfate, 98. 3% total water soluble Zn), and Zn27 (Zn oxysulfate, 66.4% total water solu ble Zn). While ZnFe,(Zn iron ferrite, 0.3% total water soluble Zn), ZnK (Zn oxide, K061, 1% total water soluble Zn), and ZnOS (Zn oxysulfate, 0.7% tot al water soluble Zn) were less effective followed by Zn40 (Zn oxysulfate, 2 6.5% total water soluble Zn) and ZnOxS (Zn oxysulfate, 11% total water solu ble Zn). The same trend was observed for Zn concentration and uptake. Regre ssion correlations showed that the higher the water solubility, the more ef fective the Zn fertilizer in increasing dry matter production. Assuming tha t 5 to 10 kg Zn ha(-1) are the rates commonly recommended, about 50% water soluble Zn is required to adequately supply the crop's needs. Lower fertili zer rates were needed as Zn solubility increased. The cadmium (Cd) and lead (Pb) concentrations and uptakes in corn forage were not significant for an y of the sources and rates.