Potassium in Atlantic Coastal Plain Soils. I. Soil characterization and distribution of potassium.
Parker D.R. | Sparks D.L. | Hendricks G.J. | Sadusky M.C.
Corn (Zea mays L.) grown on sandy Atlantic Coastal Plain soils is often unresponsive to applications of K fertilizer. As a 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 (greater than or equal to 2.0%) organic matter contents, and had correspondingly low cation exchange capacities (1 to 4 cmolc 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 cmolc 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.
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