Improving the Reliability of Soil Potassium Testing and Recommendations


RESEARCH JUSTIFICATION There is a long history of potassium (K) soil testing and management in Iowa and the North-Central Region. A period of especially extensive and diverse research extended from the late 1950s to the middle 1970s, especially with work in Illinois, Indiana, and Iowa but also in other states. During these years there was a great deal of basic K chemistry and mineralogy studies and also field applied research focusing on soil K testing and crop response to K fertilization. Read more

Year of initiation:2013
Year of completion:?

Interpretive Summary

This project is in its final stages and the Potassium (K) Fellow is completing data management and statistical analyses. The study has two major objectives. The first objective is to study the relationships among soil-test K, non-exchangeable K, and relevant properties of soils of the western humid Corn-Belt (those with large acreages dedicated to corn and soybean production). Chemical and mineralogical analyses were completed for 23 soils.

The goal of this project is to improve soil testing for potassium (K) and the assessment of crop K fertilization needs. There is much more uncertainty in the use of soil testing for K than for phosphorus (P). For example, we hypothesize that processes involving the so-called non-exchangeable soil K pool and the residue K pools have much more important impacts on soil-test K levels variation between two crops and crop response to K fertilization than is generally recognized.

The project is in its third year, and its goals are to combine basic research to characterize fundamental chemical processes with field research to improve use of soil testing for K and K fertilizer management for corn and soybean in selected soils of the North Central Region. Three complementary studies are in different stages of development.

The project is in its second year of activity. The objectives are to study relationships among soil-test K measured on dried and field-moist samples, non-exchangeable K, and mineralogy under controlled conditions for soil samples taken from contrasting soils of the Corn Belt and at Iowa field trials by considering crop K removal, while assessing temporal soil K variation. The project consists of three portions which are in different stages of development.

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Project Description

Project Leader

Antonio Mallarino, Iowa State University

Project Cooperators

Ryan Oltmans
Michael Thompson

IPNI Staff

T. S. Murrell


Americas \ Northern America \ USA \ Iowa



Potassium (K)