Conversion Factors Needed for Common Fertilizer Calculations

Introduction

The world is a big place and farmers, industry, government, and others likely use different units, oxidation states, and measurements when calculating and reporting nutrient use for farming systems. The following table outlines some of the most common conversions needed for nutrient management. For instance, to convert K to K₂O, you would multiply your K number by 1.2051. So, a fertilizer being reported as 49.8% K is also commonly reported as 49.8% × 1.2051 = 60% K₂O. Therefore, you are equally correct to report muriate of potash (KCl) fertilizer as 49.8% K or 60% K₂O, as long as you have the correct unit represented. However, note that fertilizer law generally states that certain oxidation states should be reported for certain nutrients (i.e. K₂O must be used on Virginia fertilizer labels).

References

Alley, M.M. 2000. “Part VIII: Fertilizers.” Agronomy Handbook. Publication 424-100. Virginia Cooperative Extension, Blacksburg.

American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America. 2020. “Chapter 7: Units and Measurements.” Publications Handbook & Style Manuel. Madison, WI.

Acknowledgements

Funding for this work was provided in part by the Virginia Agricultural Experiment Station and the Hatch program of the National Institute of Food and Agriculture, US Department of Agriculture.