Soil test potassium changes over time following fall potassium application in three western Kentucky soils

Abstract

Abstract Field experiments were conducted under bare‐ground conditions to investigate changes in soil test K levels over 2 yr following fall K applications to Crider, Zanesville, and Grenada soils in western Kentucky. Additional laboratory studies investigated particle size and clay mineralogy of these soils. In field experiments, highest soil test K in the Crider and Zanesville soils occurred 12–15 mo after fall K application. However, seasonal fluctuations in soil test K occurred in all three soils, likely due to fluctuations in precipitation prior to sampling. The Crider and Zanesville soils showed a much more substantial drop in soil test K at 9 and 21 mo after December K application than did the Grenada soil. The 9‐ and 21‐mo samplings were both preceded by 1–2 mo of dry conditions where precipitation was well below the 30‐yr average at the Crider and Zanesville sites. Particle size analysis showed that the Crider and Zanesville soils had a higher clay content than the Grenada soil. Soils with higher amounts of clay particles such as vermiculite have greater potential to trap K during dry periods, making soil test K levels lower than they might be under better soil moisture conditions. Over the course of these experiments, the Crider soil appeared to be more responsive to fall K application than the other soils, showing the greatest increase in soil test K by the following spring. This research illustrates the seasonal fluctuations in soil test K levels that occur naturally in these soils and how precipitation and clay content may influence these fluctuations.