Long-Term Phosphorus and Potassium Application to Corn on Coastal Plain Soils

Abstract

The effect of long-term fertilizer applications on soil test levels, yield, and crop removal depends on soil texture and mineralogy. The objectives of this study were to measure the fluctuations in soil P and K in soils of varying texture and to evaluate the usefulness of the Mehlich-1 soil extractant in predicting yield response. A field experiment was conducted for 11 yr on two soils : a Tifton loamy sand (fine-loamy, siliceous, thermic Plinthic Kandiudults) and a Greenville sandy clay loam (clayey, kaolinitic, thermic Rhodic Kandiudults). Phosphorus treatments were 0, 92, 183, and 275 lb P 2 O 5 lb/acre in the first year followed by annual applications of 0, 37, 73, and 0 lb/acre, respectively. Potassium treatments were 0, 48, 96, and 144 lb K 2 O/acre in the first year followed by annual applications of 0, 48, 96, and 0 lb/acre, respectively. Soil samples (0-6 in.) were collected each year at tasseling of the corn (Zea mays L.) crop, P and K concentrations were determined in soil and grain samples, and yield was measured. Initial application rates influenced initial soil test levels, and annual application rates affected the rate of change of soil test levels with time. All significant yield increases on the Greenville soil were due to P application. Phosphorus moves rapidly from solution into less available forms in the Greenville soil due to the soil's high P fixing capacity. Yield increases on the Tifton soil resulted from K applications, presumably due to greater leaching losses on the sandier textured soil. The Mehlich-1 extractant provides a questionable measure of soil P availability for corn. Particularly in areas where P runoff potential is high, P fertilizer should not be applied to irrigated corn in the Southeast unless the Mehlich-1 extractable soil P concentration ≤ 12 lb/acre. Data from this long-term study show that accounting for soil K below the plow layer may improve the use of mehlich-1 extractant as a measure of K availability for corn.