Zinc Soil Test Calibration Based on 0.1 N HCl Extractable Zinc and Cation Exchange Capacity from Upland Soils of Northern Nigeria
A soil-zinc calibration test study based on 0.1 N HCl extractable zinc and Cation Exchange Capacity (CEC) was carried out with upland soils of Northern Nigeria using maize (Zea mays L. moench) as a test crop. Treatments consisted of (I) no zinc and (ii) 10 mg kg-1 Zn (greenhouse) and five levels of Zn as ZnSO4. 7 H2O (field) replicated 3 and 6 times in a randomized complete block design respectively. Plant zinc concentration increased with levels of applied Zn. Higher zinc concentrations were observed in plants that received Zn application. Extractable Zn concentration increased with an increase in CEC. A positive correlation was also observed between extractable Zn and pH. HCl extractable-Zn correlated positively and significantly with Zn uptake in the first and second crops (r = +0.735** and +0.575**), respectively. The amount of Zn extracted by 0.5 N HCl was also significantly correlated with CEC. The amount of Zn extracted by 0.1 N HCl was significantly correlated with the Zn uptake by the first and second crop. The regression equations obtained from this study indicated that the distribution of ions in the exchange site of soils should be considered in estimating plant Zn requirements in soils of the northern Nigeria. However available information on the soil CEC can be used to estimate or predict the Zn concentration of the plant tissue. Critical limits may not be required in estimating or interpreting plant Zn fertilization, as regression equations are more reliable and not empirical.
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