An Evaluation of the Changes in Soil Test Potassium in Kentucky Soils Following Incubation and the Addition of 6 K Fertilizer Rates.

Agronomically, it is important to understand how potassium fertilization and crop removal will affect future soil test levels.  However, different soils do not all respond equally to K fertilization. A study was conducted (i) to determine the soil test response of Kentucky soil series to the addition of K fertilizer and (ii) to gain a better understanding of soil K status below the plow layer. Agriculturally important series were selected across Kentucky, based upon low existing test values. Soil profiles were sampled and tested for Mehlich III extractable K (STK) for depths of 0-10, 10-20, 20-30, and 30-60cm. A 10 kg sample was collected at each site from the surface 10 cm for laboratory incubation.  To evaluate changes in STK, 50 g aliquots of soil were placed in 120 ml cups and KCL was added at 0, 50, 100, 150, 200, and 250 mg K/kg. To simulate field conditions, each cup was moistened to 70% of the soil’s water content at 33 kPa and incubated for 4 wk. After 4 wk, cups were rewet and incubated for another 4 wk, and then extracted for STK. Subsurface STK varied significantly across the state.  Incubation results exhibit a significant soil series by fertilizer rate interaction.  The results provide new insights that will improve K recommendations in Kentucky.