Extreme temporal and spatial variability of soil test potassium values (STK) was measured on small plots (12-ft x 40-ft) being used for a STK correlation and calibration study on a Crider soil in Larue County, Kentucky. Twelve periodic samplings of the 20 small plots in this study over a period of 18 months showed as much as two-fold temporal differences in STK within individual plots, many of which had received no potassium (K) fertilizer during the study. Spatial variability of STK also varied as much as two-fold among the individual small plots at any given sampling time for similar treatments. Such differences of STK values from the same site could cause wide variations in recommendations for rates of K fertilizers needed. Several possible sources of this variability were considered for further investigation.
Wells, Kenneth L. and Dollarhide, James E., "The Effect of Drying Soil Samples on Soil Test Potassium Values" (2000). Agronomy Notes. 6.