Spatial Distribution of Extractable Phosphorus, Potassium, and Magnesium as Influenced by Fertilizer and Tall Fescue Endophyte Status

Abstract

Animals influence nutrient cycling within grazed systems, and the effect may be greater with tall fescue (Festuca arundinacea Schreb.) because of endophyte‐produced alkaloids that cause fescue toxicosis and alter animal behavior. Twelve grazed tall fescue pastures, established in a Cecil sandy loam (fine, kaolinitic, thermic Typic Kanhapludult) soil near Watkinsville, GA were used to measure fertility (134–15–56 and 336–37–139 kg N–P–K ha−1 yr−1) and endophyte (low, 0 to 29% and high, 65 to 94%) effects on P and K distribution. Soil samples were collected in winter 1997 at distances of 1, 10, 30, 50, and 80 m from permanently located shade and water sources at eight depth increments down to 1.5 m. Nutrient accumulation was greatest 1 m from shade and water sources where P, K, and Mg concentrations were 1.7 to 8, 2.5 to 15, and 1.1 to 1.5 times greater than average concentrations at the remaining distances, depending on depth and fertility level. Accumulation of P, K, and Mg in the area 10 to 80 m from shade and water was limited. When summed for the 0‐ to 300‐mm depth and estimated on a per hectare basis, extractable P was 64% greater in high than in low endophyte‐infected tall fescue pastures at 1 m from shade and water sources (703 vs. 428 kg ha−1, LSD = 93) and averaged 252 kg ha−1 for remaining distances. Endophyte levels did not affect K distribution and only affected Mg distribution under the low‐fertility treatment. Endophyte effects accrued over a long time period, which would indicate that altering grazing and pasture management (movement of animals, fertilizer and lime applications, and location of shade and water sources) to reduce these effects would be needed only occasionally to reduce potential environmental risks.