Potassium in Atlantic Coastal Plain Soils: I. Soil Characterization and Distribution of Potassium

Abstract

Abstract Corn ( Zea mays L.) grown on sandy Atlantic Coastal Plain soils is often unresponsive to applications of K fertilizer. As part of a field study on the response of irrigated, intensively managed corn to K applications, we characterized four representative Hapludults from the Delaware Coastal Plain and evaluated their K status. The soils were generally quite sandy with maximum clay contents of 11.4 to 26.5%, had low (≤2.0%) organic matter contents, and had correspondingly low cation exchange capacities (1 to 4 cmol c kg −1 by summation). The clay fractions were dominated by kaolinite and hydroxy‐interlayered 2:1 expansible minerals; the latter may play a crucial role in the overall chemistry of K in these soils. The soils were quite high in total K, with means for the four soils (across horizons) ranging from 23.6 to 43.9 cmol c kg −1 , and this was ascribed to the K‐rich parent material and relatively young age of these soils. Most (97–98%) of the total K was in mineral forms, and the majority (65–87%) was in the sand fractions, virtually all as K‐feldspars. Exchangeable and nonexchangeable (fixed) K levels were relatively low and were of comparable magnitude. Consideration of particle size distribution, K distributions, and published studies of weathering rates suggested that the sand fractions of these soils represent significant sources of plant‐available K.