POTASSIUM QUANTITY-INTENSITY RELATIONSHIPS IN THE PRESENCE AND ABSENCE OF NH4 FOR 3 KENTUCKY SOILS

Potassium-Ca exchange reactions in soils are often investigated in laboratory-type studies. It is assumed that results from such binary exchange systems can be extrapolated to three-ion (ternary) systems by using appropriate equations. However, such an evaluation is rarely carried out. This study investigated the influence of added ammonium (NH4) on potassium quantity-intensity (Q/I) relationships representing adsorption and desorption by soil samples taken at the 0 to 15-cm and 15 to 30-cm depths for three soils obtained from northern Kentucky. The soils were Eden silty clay (fine, mixed, mesic Typic Hapludalfs), Lowell silty clay loam (fine, mixed, mesic Typic Hapludalfs), and Nicholson silt loam (fine, mixed, mesic Typic Fragiudalfs). These soils have each failed to show K-fertilization response. It was shown that the Q/I plot components, labile K (Ex(K)0), activity ratio of K at equilibrium (AR(K)0) and linear potential buffering capacity of K (PBC(K)) were each affected by added NH4. The addition of NH4 caused an increase in the quantity of labile K for all three soils at both depths. AR(K)0 was also higher in the presence of NH4, but the PBC(K) was lower. The amount of K extracted with 0.1 mol L-1 BaCl2 was closer to the amount of K estimated from the y-intercept of the Q/I plot of the apparent high-affinity sites than to the amount of K extracted with neutral NH4C2H3O2. Finally, K adsorption was not readily reversible. The quantity of K desorbed was higher in the presence of added NH4 than in its absence. The availability of K in these soils should be enhanced by the presence of ammonium in the soil solution.