Some concern has developed during recent years that fertilizer is being used by farmers on fields with residual levels of P and K high enough that such use is not justified as a means of increasing crop yields. This has been due to increased "average" soil test values for samples routinely submitted to college soil test laboratories.
For this reason, studies were conducted in Graves and Todd Counties in Kentucky during the period September, 1978 to September, 1980, to determine if soil samples routinely submitted to college test laboratories do or do not accurately reflect the average soil fertility status of a county.
Wells, Kenneth L.; Peaslee, D. E.; Davidson, Marvin; and Green, William, "An Estimate of the Soil Fertility Status of Graves and Todd Counties in Kentucky" (1983). Agronomy Notes. 82.