Potassium Uptake by Corn and Soybean, Recycling to Soil, and Impact on Soil Test Potassium

Research is needed to quantify better plant nutrients recycling to the soil. This study investigated K recycling by corn ( Zea mays L.) and soybean [ Glycine max (L.) Merr.] from physiological maturity (PM) to spring. Aboveground plant samples were collected from 19 Iowa K field response trials (33 sites years for corn and 14 for soybean). Dry matter (DM) yield and K accumulation were measured in vegetative tissue at PM, in all tissues at grain harvest, and in residue four times until spring. Soil test K (STK) was measured at grain harvest each year and in the last 2 yr the following spring. On average, K accumulation in grain or residue at harvest was 68 and 34 kg K ha −1 in soybean and 29 and 52 kg K ha −1 in corn. The K accumulation increase from fertilization was more frequent and greater in residue than in grain (60 and 9% for soybean and 57 and 7% for corn). Potassium accumulated in vegetative tissue at PM that remained in residue 2 mo after harvest was 50% in corn and 19% in soybean and decreased to 31 and 12% by April. The K loss decreased as precipitation increased ( R 2 0.64 for soybean and 0.38 for corn) and affected more the K loss in soybean than corn. Soil test K increased from fall to spring, and the increase was related to the K lost from residue ( r 2 0.56 in soybean and 0.16 in corn). Crop type and precipitation strongly influenced K recycling and affected STK temporal variation.