NPK fertilizers are mainly comprised of three primary nutrients required for a healthy plant growth (nitrogen, phosphorous, potassium). They are available as liquid, or granular form, whereof the last is the most common used one. Knowing the quality and content of a fertilizer allows an optimal utilization for a planned culture and optimizing the amount of used fertilizer. This helps to reduce costs and to improve plant growth and with it, a better harvest follows.
To assess potassium, several methods like flame photometry, titration, or ion measurement can be used. In this work, the potassium content is measured by standard addition which is a fast, inexpensive, and easy to use method.