Effect of Long-term Tillage Systems and Nitrogen Addition on Potassium Quantity-Intensity Relationships

The no-tillage (NT) management of soils is expected to have an influence on the K⁺ adsorption characteristics of these soils due to organic matter accumulation. The purpose of this study is to investigate this influence as affected by nitrogen (N) additions. The effect of 16 yr continuous corn (Zea mays L.) production under conventional tillage and no-tillage management on potassium quantity-intensity (Q/I) relationships was investigated on soil samples taken at 0–50 mm and 50–150-mm depths of a Maury silt loam (fine-silty, mixed, mesic Typic Paleudalfs) from central Kentucky. The results show that the Q/I plot components, labile K⁺, activity ratio for K⁺ at equilibrium (ARKₒ) and linear potential buffering capacity for K⁺ (PBCK) were affected by tillage and N additions. The no-tillage soil with and without N fertilizer had the highest quantity of labile K⁺ at the 0–50 and 50–100-mm depth. The ARKₒ was also the highest for the no-tillage with and without N in comparison to conventional tillage for the two depths. The highest PBCK value was that of conventional tillage no N at the 0–50-mm depth. The lowest PBCK value was that of no-tillage no N also at the 0–50-mm depth. The BaCl₂ CEC determination along with the relative affinity for K⁺ (determined from the slope of plots of ExK/CEC vs. ARK; where ExK = BaCl₂ extractable K⁺) were the best predictors of the relationship PBCK = CEC KGₒ. The relative affinity for K at the linear portion of the Q/I plots appears to be influenced by organic matter content and pH. Finally, the increase in organic matter content is shown to have a positive influence on the magnitude of high affinity K⁺ sites. Contribution from the Dep. of Agronomy. Univ. of Kentucky Agric. Exp. Stn. The investigation reported in this paper (no. 87-3-192) is in connection with a project of the Ky. Agric. Exp. Stn. and is published with the approval of the director.