© 2005 Plant Management Network. Accepted for publication 25 October 2005. Published 20 December 2005. Nitrogen Rate and Source Effects on the Yield and Nutritive Value of Tall Fescue Stockpiled for W inter Grazing Chris D. Teutsch, Assistant Professor, Southern Piedmont Agricultural Research and Extension Center, Virginia Polytechnic Institute and State University, Blackstone 23824; John H. Fike, Assistant Professor, Crop and Soil Environmental Sciences, Virginia Polytechnic Institute and State University, Blacksburg 24061; Gordon E. Groover, Extension Economist, Department of Agricultural and Applied Economics, Vir g inia Polytechnic Institute and State University, Blacksburg 24061; and Susanne Aref, Director, Statistical Consultin g Center, Department of Statistics, Virginia Polytechnic Institute and State University, Blacksburg 24061 Corresponding author: Chris D. Teutsch. cteutsch@vt.edu Teutsch, C. D., Fike, J. H., Groover, G. E., and Aref, S. 2005. Nitrogen rate and source effects on the yield and nutritive value of tall fescue stockpiled for winter grazing. Online. Forage and Grazinglands doi:10.1094/FG-2005-1220-01-RS. Abstract Late summer nitrogen fertilization is a primary factor affecting yield of cool- season pastures allowed to accumulate herbage for deferred grazing. Attention has been given to the quantity of N applied, but the source of N has not been investigated. This study evaluated the effects of N rate and source on yield and nutritive value of stockpiled tall fescue. Trials were conducted on two farms located near Amelia, VA in 2002 and 2003 and Blackstone, VA in 2004. Six N sources (ammonium nitrate, ammonium sulfate, broiler litter, complete fertilizer, urea, and urea-ammonium nitrate) were applied at 0, 40, 80, and 120 lb plant available N per acre in mid-August. Forage was allowed to accumulate until mid- December. Yield increased linearly with N rate for each N source, but the rate of increase varied from 5 to 13 lb DM/lb of N. Compared to the unfertilized control, yield at the highest N rate was increased 25 to 61% depending on nitrogen source. Ammonium nitrate and ammonium sulfate were the most effective N sources for stockpiling tall fescue. Urea-ammonium nitrate produced the lowest yield and would not be a suitable replacement for ammonium nitrate, even when applied at higher rates. Tall fescue ( Lolium arundinacea (Schreb.) S.J. Darbyshire) is grown on more than 24 million acres in the east-central and southeastern United States (5). It is the primary forage base for more than 9 million beef cows in this region (8). One of tall fescue’s strongest and most under-utilized attributes is its ability to be stockpiled for winter grazing (Fig. 1). Agronomic factors that affect stockpiled tall fescue production were reviewed b y Matches (7) more than 25 years ago and more recently by Poore et al. (10). A primary factor affecting yield was N fertilization. Response of tall fescue to autumn N applications is highly variable due to environmental conditions. In general, 10 to 20 lb of forage DM production per lb N can be achieved with moderate N inputs (55 to 110 lb of N per acre) (10). While a substantial amount of research has examined N rate effects on stockpiled tall fescue production, little research has evaluated the effect of N source. This study was designed to determine the effect of N source and rate on the yield and nutritive value of stockpiled tall fescue. 20 December 2005 Forage and Grazinglands Published January 29, 2014