Zinc Fertilizer Test Kit for Semi-Quantitative Verification of Fertilizer Quality

Zinc (Zn) addition is often recommended for rice culture, but the quality of Zn fertilizer is variable. A semi-quantitative test kit was developed from a zincon colorimetric method to provide buyers an estimate of Zn content in zinc sulfate or zinc oxide fertilizers. The kit includes tools for sample dilution, capsules with sufficient zincon and borax buffer reagent for color development of one sample, and a five-panel color chart to categorize the sample at 0, 5, 10, 15, or 20% Zn. An analysis of user errors indicated that water impurity would cause the most significant problem, resulting in errors of one color category or more. The errors associated with the semi-quantitative measurements of fertilizer and water using tools provided in the kit did not cause significant problems affecting the final color category of the fertilizer, making the kit an acceptable method of estimating Zn content of granular fertilizers.