Missouri Fertilizer and Lime Council Enhancing Macronutrient Concentrations in Stockpiled Tall Fescue with Phosphorus Fertilization Final Report Dale Blevins and Will McClain Division of Plant Sciences University of Missouri Abstract Tall fescue (Festuca arundinacea) is a popular cool season grass used for beef production. Stockpiling tall fescue pasture is recommended for extending the grazing season and reducing winter-feeding costs. Our previous work indicated that stockpiled tall fescue leaves had low concentrations (< 0.2%) of P and magnesium (Mg) in late winter even after applications of 25 lbs P/acre. The objective of this study was to determine if high rates of P fertilization would maintain leaf P and Mg concentrations above the target 0.2% required by lactating beef cows throughout the stockpiling period. Leaf concentrations of P, Mg, and calcium (Ca) were higher with P fertilization than those of the untreated controls. The 200 lbs P/acre treatment maintained leaf P and Mg concentrations at or above the target 0.2% level during the first year of the experiment. The leaf concentrations of P, Mg, and potassium (K) declined from October to February with all treatments. The decrease in leaf concentrations of phloem mobile elements like P, Mg, and K may be the result of nutrient remobilization from leaves to roots during the late fall and early winter as strategy to provide support for next springs growth.Introduction Tall Fescue (Festuca arundinacea) is a popular cool season grass used for beef production. Stockpiling tall fescue is recommended for extending the grazing season and reducing winter-feeding costs. The hardy nature of tall fescue and its ability to maintain growth with the onset of cooler temperatures as well as its wide range of adaptability for soil types and climatic conditions make it excellent forage for stockpiled systems (19,18,13). Tall fescue persists with little or no management owing to its adaptability, nevertheless on many soils yields can be enhanced by fertilization. Gerrish et al. (8) increased yields of stockpiled tall fescue up to 35% with nitrogen (N) fertilization. Although Archer and Decker (1,2) stimulated growth and crude protein (CP) of tall fescue with N fertilization, overall forage quality was not affected. More recently, Singer et al. (17) found that a late season application of N increased the quality and quantity of stockpiled tall fescue. These researchers pointed out, however, that harvests delayed beyond October could incur losses to quality as well as yield. In Missouri, the majority of pasture soils are low in plant available phosphorus (P) (9). Forage production on such soils may impact the nutrient concentrations of stockpiled tall fescue leaves. Studies in Tennessee and West Virginia found that nutrient concentrations in tall fescue leaves declined through the winter months (4,14,15,6,7). Previous work by Reinbott and Blevins (12,13) indicated that P fertilization improved nutrient concentrations in tall fescue leaves in southwest Missouri. However there are no reports of fertilization on improvement of nutrient quality of stockpiled tall fescue. Currently beef producers compensate for nutrient deficiencies in forages by supplementing the diets of livestock grazing in winter and early spring. Managing pastures in a practical and cost effective manner that improves the nutrient concentrations in tall fescueleaves would benefit beef producers in regions with low soil P. Therefore the objective of this research is to improve the nutrient concentrations of stockpiled tall fescue during winter and early spring with P fertilization. Setting Up a Stockpiled Tall Fescue Field Study The two-year study was conducted on an established tall fescue pasture at the University of Missouri Southwest Research Center near Mt. Vernon, Missouri (37º 04’N 93º 53’W elevation 1150 ft) on a Creldon silty clay loam (fine, mixed, active, mesic, Oxyaquic, Fragiudalf). The site was typical of southwest Missouri in that the soil is low in plant available P, 7 lbs/acre Bray I, and had the following test results: pH 5.3; O.M.2.8 %; Ca 2748 lbs/acre; Mg 280 lbs/acre; and K 446 lbs/acre. Treatments. In August the forage was removed from the pasture and 10’ x 25’ plots with 5’ alleys were laid out in six replicate blocks. Treatments consisted of 0, 50, 100, and 200 lbs P/acre in the form of triple super phosphate (46% P2O5). Each treatment was randomly applied to plots in all six blocks and the entire area received 100 lbs N/acre in the form of ammonium nitrate. In August of the second year of the experiment, the forage was again removed and a 100 lbs N was applied. At the end of each year, soil samples were taken to determine the changes in soil P. Harvests and Mineral Analyses. Beginning in mid-October through April of both years, twenty of the most recently collared leaves were harvested from each plot. All samples were oven dried, ground, and digested in nitric acid with a microwave accelerated digestion system (5). Digested samples were filtered, diluted, and analyzed for nutrient content. Potassium was determined by flame ionization, Ca and Mg by atomic absorption, and P by colorimetric analysis. In November of the first year ten of the most recently collared leaves were measured for each plot.Statistical Analysis. The experiment was a completely randomized blocks design analyzed as a split-split plot in time model with repeated measures. This model was used to test for statistical significance of P treatment effects as well as interactions with month using PROC MIXED in SAS version 9.1 (16). Main plot consisted of P treatment; harvest date was considered the split plot and year the split-split plot. Fertilization treatment was a fixed effect factor and year, month, and block were treated as random factors. Macronutrients in Stockpiled Tall Fescue Leaves Leaf Growth in Response to P Fertilization. In fall of the first year of this study, P fertilization produced remarkable tall fescue leaf growth (Fig. 1). Leaf growth exhibited an increasing response to all P treatments, with the leaves from the 200 lb P treatment being twice as long as those from the untreated control plots (Fig. 2). It is possible that the Creldon soil in this pasture, with high concentrations of aluminum, manganese, and iron may be influenced by high rates of P fertilization, in that P could ameliorate the toxic effects of these metals. Phosphorus. Across