“Potassium Paradox” Questions
What does an agronomist or crop consultant do when researchers at a major land grant university claim existing soil tests for potassium are so faulty as to have little if any value? As a full-service ag retailer, how do you respond to their argument that “an extensive survey of more than 2,100 yield response trials confirmed that KCl (potassium chloride) fertilization is unlikely to increase crop yield.” With the research only published this past October, the entire issue may still be news to you, but it is a subject likely to come up with customers. To date, little discussion has been had ... publicly.
“There has been a noticeable silence,” said Richard Mulvaney, co-author of “The Potassium Paradox: Implications for Soil Fertility, Crop Production and Human Health.” “The public deserves a scientific discussion of the data.”
Why the silence? It is not for lack of author credentials, depth of material, nor for lack of review. Lead author Saeed Khan, Mulvaney and Timothy Ellsworth are all professors in the Department of Natural Resources and Environmental Sciences, University of Illinois, Urbana-Champaign. The paper cites 500 peer-reviewed, university-produced research papers on the subject of KCl. First submitted to the Soil Science Society of America Journal in 2012, peer reviewers recommended against publishing without giving any science-based reasons. The authors then turned to Renewable Agriculture and Food Systems, a less well-known journal, but one willing to present the controversial findings.
“The Potassium Paradox” revisited research Khan carried out for his Ph.D. in the late 1980s. It included multi-sample, bi-weekly soil sampling for K in corn/soybean rotation plots, including one that had received no K fertilizer for 15 years. Sampling was carried out year round from March 1986 to March 1990. Soil K testing was performed on the field-moist samples before and after air-drying, common practice for commercial labs.
Variations from day to day throughout the year and throughout the four years were dramatic, as were the variations between test results. However, both tests showed steadily increasing K levels in the plot where no K was applied.
“I told my advisor that soil K testing does not work,” recalled Khan.
Due to Khan’s return to work in Pakistan and health issues of his advisor, the research was never published. Nearly 20 years passed until Khan worked with Mulvaney and Ellsworth on several projects related to soil nitrogen management. Discussions led them to review his earlier research and the published literature concerning KCl fertilization. The three researchers agreed on the importance of a comprehensive review of the scientific literature and were careful to focus their efforts on peer-reviewed and university publications as the most objective resource available. The process took five years.
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