Shade and N Effects on Tall Fescue Production and Quality

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.