The deficiency of zinc (Zn) in human nutrition, commonly found in cereal-based diets accounts for impaired growth (stunting) in children. Since cereals are generally low in this element, bio-fortification may represent an opportunity to increase Zn intake by humans. A study was carried out to evaluate Zn uptake by maize and wheat when they are supplied with increasing rates of foliar or soil applied Zn. Maize and wheat were grown in the field and supplied with 0, 10, 20, 30, or 40 kg Zn ha-1 as ZnSO4 applied to the soil, or, 0,1,2,4, or 8 kg Zn ha-1 as foliar spray. Zinc application to soil increased maize and wheat yields beyond increments obtained with foliar application, but Zn mass concentration in maize grain was better with foliar applications. Mean maize yield was 1.78 ton ha-1 with soil application and 1.14 ton ha-1 with foliar application. This was in relation to an average of 52 mg Zn uptake by maize under each of the application methods. Wheat yield was 3.69 ton ha-1 under soil application and 2.74 ton ha-1 under foliar application. In this case, Zn uptake was higher under soil application (11.31 mg) than under foliar application (7.25 mg). Sesquioxide bound Zn was shown to be best correlated with plant Zn uptake. It was shown that Zn application is beneficial on Zambian soils, and while soil application increases crop yields, foliar application can be more useful to increase Zn mass concentration in maize.
Key words: Foliar spray, maize grain yield, wheat grain yield, zinc fractions, zinc uptake
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