Quantity‐intensity parameters of potassium in relation to uptake by guinea‐corn in representative soils of the ecological zones of Nigeria

Abstract

Quantity‐intensity (Q‐I) relation studies were often used to supplement information obtained from conventional soil tests for the estimation of potassium (K) needs of crops. With a view to ascertaining the reliability of the Q‐I relation parameters for comprehensive characterization of K dynamics in typical Nigerian soils, K values derived from Q‐I isotherms were related to neutral normal ammonium acetate (1 N NH4OAc, pH 7.0) (exchangeable) K, other soil K forms [non‐exchangeable (Kne), exchange (Ke), mineral K (K m ), and solution K (Ks)] and the K uptake by Guinea‐corn (Sorghum bicolor, var. LS 187) subjected to weekly cuts in Neubauer cultivation vessels. Most of the soil K (about 98%) was in the form of soil minerals while less than 1% was plant available whereas about 1% was trapped within the interlattice layers of the clay minerals (as fixed K or Kne). Mineral K (Km) content was closely related to total K (Kt), but not to the other forms, Kne, Ke, and Ks. A close relationship was noted between the two components of labile K (Ke and Ks). Except for % K saturation, the relationships between the K measurements with plant response were poor. The results of these investigations clearly demonstrate that the Q‐I relation could not adequately characterize the K dynamics of these tropical soils.