The potassium paradox: Implications for soil fertility, crop production and human health

S. A. Khan, R. L. Mulvaney, T. R. Ellsworth

Research output: Contribution to journalArticlepeer-review


Intensive fertilizer usage of KCl has been inculcated as a prerequisite for maximizing crop yield and quality, and relies on a soil test for exchangeable K in the plow layer to ensure that soil productivity will not be limited by nutrient depletion. The interpretive value of this soil test was rigorously evaluated by: (1) field sampling to quantify biweekly changes and seasonal trends, (2) characterizing the variability induced by air drying and the dynamic nature of soil K reserves and (3) calculating the K balance in numerous cropping experiments. These evaluations leave no alternative but to question the practical utility of soil K testing because test values cannot account for the highly dynamic interchange between exchangeable and non-exchangeable K, exhibit serious temporal instability with or without air drying and do not differentiate soil K buildup from depletion. The need for routine K fertilization should also be questioned, considering the magnitude and inorganic occurrence of profile reserves, the recycling of K in crop residues and the preferential nature of K uptake. An extensive survey of more than 2100 yield response trials confirmed that KCl fertilization is unlikely to increase crop yield. Contrary to the inculcated perception of KCl as a qualitative commodity, more than 1400 field trials predominately documented a detrimental effect of this fertilizer on the quality of major food, feed and fiber crops, with serious implications for soil productivity and human health.

Original languageEnglish (US)
Pages (from-to)3-27
Number of pages25
JournalRenewable Agriculture and Food Systems
Issue number1
StatePublished - Mar 2014


  • Cd bioaccumulation
  • KCl
  • Morrow Plots
  • agricultural sustainability
  • potash fertilizer
  • residue K recycling
  • soil K reserves
  • soil K testing

ASJC Scopus subject areas

  • Food Science
  • Agronomy and Crop Science


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