Potassium in Atlantic Coastal Plain Soils: II. Crop Responses and Changes in Soil Potassium Under Intensive Management

Corn (Zea mays L.) grown on sandy Atlantic Coastal Plain soils is often unresponsive to applications of K fertilizer. The purpose of this investigation was to examine the response of irrigated, intensively managed corn to K applications, and to monitor changes in soil K status. Field studies were conducted for 3 yr at four sites on the Delaware Coastal Plain. Treatments consisted of 0, 94, or 282 kg haapplied K, both as a single application and in three split applications. Grain yields were high (6.9 to 14.0 Mg ha-), but were not significantly (p < 0.05) affected by K application for any yearsite combination. Similarly, corn ear leaves at silking contained adequate K (20 to 30 mg kg-), although these concentrations varied with K application rate on the two sandier soils. In the zero K plots, dilute double acid-extractable K concentrations ranged from 56 to 194 mg kgat the start of the study, and had declined by 29 to 45% by the end of the third growing season. Evidence was obtained for both leaching of applied K and conversion to nonexchangeable forms. The lack of observed yield response was ascribed to (i) modest crop removal of K when corn is harvested only for grain, (ii) adequate Kbuffering capacity of these soils to meet high crop demands during the growing season, and/or (iii) availability of significant quantities of subsoil K. Our results further suggested that, despite the high grain yields obtained, current recommendations by several state soil testing laboratories in the region are, if anything, somewhat excessive in that K fertilizer is recommended even when no yield response