Phosphorus Fertilization Increased Macronutrient Concentrations in Leaves of Stockpiled Tall Fescue

Abstract

Beef producers utilize stockpiled tall fescue (Festuca arundinacea Schreb. 'Kentucky 31') in the Midwest to extend the grazing season and reduce winter feeding costs. Previous studies indicated concentrations of some macronutrients in stockpiled tall fescue leaves were below those required by lactating beef cows in late winter and early spring. Our previous studies found P fertilization in late winter increased leaf Mg and Ca concentrations in early spring. Therefore, the objective of this study was to determine the effects of 2 years of P fertilization on leaf macronutrient concentrations of stockpiled tall fescue during late fall, winter, and early spring. Leaf concentrations of P, Mg, and Ca were higher with P fertilization than those of the untreated controls. During the second year, the highest P treatment maintained leaf P and Mg concentrations above the critical 0.2% required by lactating beef cows during peak lactation. The leaf concentrations of phloem mobile macronutrients declined from October to February with the exception of N, which reached its lowest concentration in January. Decreases in leaf concentration of mobile elements like P, Mg, N, and K may be the result of nutrient remobilization from leaves to roots during late fall and early winter as a strategy to provide support for next spring's growth. Producers should account for the possibility of low leaf macronutrient concentrations in tall fescue during late winter, especially when beef cattle are grazing pastures on soils with low plant-available P.