Colorimetric Method for Determining Zinc in Granular Fertilizers and Rice Plant Tissues.

Zinc is the most common micronutrient deficiency in flooded rice. It is applied to the soil as a granular fertilizer, usually zinc sulfate or zinc oxide. Zinc fertilizers are sometimes adulterated, and it has been difficult for distributors and farmers to know if they are buying quality fertilizer. Knowledge of plant Zn status may enable farmers to add fertilizer in time to overcome Zn deficiency. The common tests for plant Zn status require a laboratory analysis, making them ineffective for timely Zn management in the field. A colorimetric method was developed for quantitatively determining Zn in fertilizer and rice plant samples using simple laboratory equipment. This method was further developed into a semi-quantitative testing kit for use in the field.