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

Dept. of Soil and Environmental Sciences, Univ. of California, Riverside, CA 92521

D. L. Sparks and G. J. Hendricks

Dep. of Plant Science, Univ. of Delaware, Newark, DE 19717-1303

M. C. Sadusky

Geo-Centers, Inc., 10903 Indian Head Way, Fort Washington, MD 20744

* Corresponding author.

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.

Published with the approval of the director of the Delaware Agric. Exp. Stn. as Miscellaneous Paper no. 1249. Contribution no. 241 of the Dep. of Plant Science, Univ. of Delaware.

Received for publication June 20, 1988.