Potassium accumulation and soybean yield related to potassium fertilizer rate and placement

Sandy coastal plain soils have relatively low reserves of potassium (K) and may not be able to supply adequate K for intensive soybean [Glycine max (L.) Merr.] production. Field experiments were conducted in 1985 on Goldsboro sandy loam (fine-loamy, siliceous, thermic Aguic Paleudult) and in 1986 and 1987 on Dothan loamy sand (fine-loamy, siliceous, thermic Plinthic Paleudult) to determine K fertilizer rate and placement effects on soybean growth and seasonal K accumulation. Treatments were 0, 56, 112, 168, and 224 kg/ha broadcast and 56 kg K/ha banded plus 0, 56, 112, and 168 kg/ha broadcast. Seasonal plant tissue K concentrations were generally increased by K fertilizer rate each year. Method of placement did not have consistent effects on plant K concentration and had little effect on total K accumulation. Grain yield responded to applied K only in 1986 when the initial exchangeable K level was 0.24 cmol/L. Both broadcast and broadcast-plus-band placement methods resulted in linear yield increases but yield was generally higher with broadcast placement. A plateau yield level was not exhibited with K rate. The 224 kg/ha broadcast treatment achieved the highest grain yield and was associated with an exchangeable K level of 0.37 cmol/L and a soil solution K concentration of 1.08 mmol/L. When soybean is grown with intensive production practices, there is little benefit to band placement of K on sandy soil testing high in K.