Crude protein and nitrate concentrations of fall forage for stocker cattle: wheat vs. perennial cool-season grasses

Winter wheat (Triticum aestivum L.) pastures are a primary source of cool-season forage used by stocker cattle (Bos taurus L.) in the southern Great Plains. Replacing some wheat pasture with perennial cool-season grasses (PCSGs) could reduce uncertainties of sufficient fall forage and annual tillage operations. Wheat forage is capable of producing stocker weight gains >1.4 kg [d.sup.-1], but wheat can accumulate nitrate that poses a health risk to stockers. Levels of crude protein (CP) and nitrate in fall forage clipped 4 yr (2002-2005), from replicated pastures of winter wheat and two PCSG pastures established in 2001 ('Jose' tall wheatgrass [Thinopyrum ponficum (Podp.) Z.-W. Liu & R.-C. Wang], 'Manska' intermediate wheatgrass [Thinopyrum intermedium (Host) Barkworth & D.R. Dewey], and one PCSG pasture established in 2002 ['Lincoln' smooth bromegrass (Bromus inermis Leyss)], were compared. Forage levels of CP in PCSGs were >148 g [kg.sup.-1] dry wt., but were 21 to 37% less than that of wheat (244 [+ or -] 3 g [kg.sup.-1]). Mean nitrate-N levels of wheat were 400, 1400, 4600, and 840 mg [kg.sup.-1] in 2002 through 2005, respectively. Among the PCSGs, nitrate-N did not exceed 660 mg [kg.sup.-1]. The CP levels of PCSGs were often substantially less than that of wheat, but were sufficient for growth of stocker calves. Nitrate risks that sometimes occurred with wheat would make PCSGs a safer choice for pasture. doi: 10.2135/cropsci2009.09.0517