Shade and N Effects on Tall Fescue Production and Quality1

Abstract Tall fescue (Festuca arundinacea Schreb) has been established on a number of areas in eastern Oklahoma, western Arkansas, and southeastern Missouri after the brush has been controlled. There have been cattle deaths attributed to nitrate‐nitrogen (NO3‐N) toxicity on these converted areas and concern that the shade from the standing brush was contributing to the problem. A 6‐year study was conducted at the western edge of the Ouachita Highland resource on soils of the Hector‐Hartsells association (Lithic Dystrochrept and Typic Hapludults) to determine what effect N fertilizer and shade would have on tall fescue forage production, crude protein, and NO3‐N concentration. The brush had been controlled with 2,4,5‐T [(2,4,5‐trichlorophenoxy)acetic acid] in 1970 and the area converted to tall fescue. February application of N fertilizer increased forage production with the greatest increase occurring with the first 50 kg/ha of applied N. Shade effect from standing dead brush was insignificant on forage production and NO3‐N concentration, but 80% shade from Saran shade cloth for 6 days increased NO3‐N concentration from 1,200 to 4,200 ppm in plots receiving 50 kg/ha of N. Nitrogen fertilizer increased NO3‐N concentration of the forage in March of both years NO3‐N was evaluated with a high of 7,500 ppm occurring for the 100 kg/ha applications of N. However, by April of both years the NO3‐ N levels in the forage from all plots were below the potentially toxic level of 2,100 ppm for cattle. Standing dead brush had a minimum effect on tall fescue production, percentage crude protein, and NO3‐N concentration so would not need to be removed from brush converted areas. The NO3‐N concentration of N fertilized plots was often above the toxic level of 2,100 ppm in March so precautions need to be exercised in grazing N fertilized tall fescue in March.