Soil Potassium Distribution in Grazed K‐31 Tall Fescue Pastures as Affected by Fertilization and Endophytic Fungus Infection Level

Fertilizer requirements of grazed pastures may be influenced by the spatial distribution of nutrients in animal excreta. This experiment was conducted to determine the effect of two levels of fertilization and endophytic fungus ( Acremonium coenophialum Morgan‐Jones et Gams) infection of Kentucky‐31 tall fescue ( Festucu arundinacea Shreb) on the lateral and vertical distribution of soil K after 3 yr of grazing. Each pasture consisted of 0.7 ha of a Cecil sandy clay loam (clayey, kaolinitic, thermic Typic Hapludult,) and was grazed using the put‐and‐take method. Forage was removed only by grazing. Endophytic fungus levels were 20% (Low endophytic fungus, LE) and 52% (high endophytic fungus HE), and fertilizer rates were 134‐15‐56 kg N‐P‐K (Low fertilizer LF), and 336‐37‐139 kg N‐P‐K ha −1 yr (high fertilizer HF) in a 2 ✕ 2 factorial replicated twice in a randomized block design. Each pasture was divided into 12 zones with each zone sampled separately to a depth of 122 cm before the grazing experiment began and then annually for 3 yr. Potassium did not accumulate in the majority of the pasture area at either fertility level except near the waterer, mineral feeder, and shade. Potassium accumulation rates in this area, determined by linear regression, were 7, 23, 23, and 46 kg K yr ‐1 for LELF, LEHF, HELF, and HEHF treatments, respectively. These amounts were equivalent to 18, 24, 59, and 47% of the fertilizer K applied to the 0.7 ha pastures for the LELF, LEHF, HELF, and HEHF treatments, respectively. This accumulation was a result of animal grazing and resting behavior. Much of the K accumulated below 15 cm. Transfer of K by grazing steers to camping zones and subsequent leaching increased with fertility level and endophyte infection level. This redistribution reduces effectiveness of K recycling under grazing, and increases fertilizer K requirements in non‐camping zones.