Fall Forage Biomass and Nitrogen Composition of Winter Wheat Populations Selected from Grain-Only and Dual-Purpose Environments

with those choosing to grow wheat as a forage-only or GO crop (Redmon et al., 1995), but they need to follow Winter wheat (Triticum aestivum L.) is the foundation of many a recommended set of management practices to optiagricultural enterprises in the southern Great Plains and is grown primarily as either a grain-only (GO) or a dual-purpose (DP, grazing mize returns. plus grain) crop. Traditionally, cultivars are developed in GO systems. When market conditions favor the forage value more Because of genotype system interactions, the DP environment may than the grain value of wheat intended for DP, the crop compromise gains in grain yield accrued in GO-developed cultivars. should be planted earlier (Hossain et al., 2003) and Forage traits for 24 sets of populations (each with unique pedigree) seeded more densely (Epplin et al., 2000) than GO were used to test benefits of tailoring breeding programs for DP wheat. To assure early fall growth, fertilizer N needed wheat. Each set came from the same F2 source and contained a base to achieve a desired grain yield plus additional N to (B) F3 bulk population and F5 bulk populations mass selected from account for N removal in consumed forage is usually the F2 within either a GO or DP system. Forage biomass and forage total N and nitrate were measured at the start of fall grazing. Nearly applied at planting (Krenzer, 1994; Zhang et al., 1998). always, the effect of selection environment was consistent across geThese DP management practices may add certain risks. netic backgrounds. Effect of selection environment on forage biomass An early planting date in the southern Great Plains of each nursery was significant at P 0.09 and P 0.07. In 2001, favors the incidence and severity of soil-borne and insect DP-derived populations produced about 5% less than GO-derived transmitted disease (Hammon et al., 1996; Hunger et populations; in 2002, the selection effect was not significant (P 0.38 al., 2002; Piccinni et al., 2001) and insect herbivory and 0.30). Selection environment had a significant effect on forage (Royer et al., 1997) and can reduce grain yields by varitotal N, but not nitrate levels. Total N in DP selections was slightly able amounts depending on the year or cultivar (Epplin greater (2.5%, P 0.05) than those from B and GO selections. Forage and Peeper, 1998; Carver et al., 2001). These disease nitrate was affected by genetic background; mean nitrate-N among the 24 backgrounds ranged from 1.3 to 3.1 mg g 1 in 2001 and 0.4 to risks are necessary, however, when the goal is to produce 1.3 mg g 1 in 2002. Selection in the DP system appears to offer equal a sufficient base of fall forage that is well anchored in or slightly less fall forage biomass without greatly changing forage the soil. Another potential risk arises from additional total N and nitrate concentrations. N fertilizer applied in the fall. The extra N can increase the nitrate levels in wheat forage (Raun and Westerman, 1991; MacKown and Weik, 2004), thereby increasing H winter wheat grown in Oklahoma and the potential health risks affecting performance of young surrounding areas of the Texas Panhandle, southgrazing ruminants (Strickland et al., 1995; Undersander ern Kansas, eastern New Mexico, and southeastern Colet al., 1999). orado is managed as GO, grazing-only, grazing plus Wheat cultivars used for DP are typically developed grain (DP), and as a hay or silage crop. Wheat pastures by wheat breeders that make selections based on perforin the southern Great Plains have a pivotal role in the mance in GO production systems rather than DP sysU.S. beef (Bos taurus L.) industry by providing the link tems. Because of genotype environment interactions for millions of fall stocker calves received annually that (Krenzer et al., 1992) and genotype production system pass from more than 500 000 farms across the southern interactions, cultivar development based solely on selecUSA to feedlots located in the Great Plains. Because tion in a GO production system may compromise gains grasslands in the southern Great Plains are dominated in genetic improvement of desirable traits for wheat by warm-season species, the predominate source of used in DP production (Khalil et al., 2002). Furthercool-season forage is wheat. Consequently, as much as more, forage and grain yields of small-grain cereals are 80% of the total wheat acreage in the southern Great uncorrelated (Ud-Din et al., 1993) or only poorly correPlains is grazed (Pinchack et al., 1996). Typically in lated (Atkins et al., 1969), which underscores the need Oklahoma, about 40% of the wheat acreage is grown to consider both forage and grain traits of wheat inas a DP crop (Hossain et al., 2004). Wheat producers tended for use as a DP crop. Because the evaluation choosing a DP management system have greater flexiand selection of wheat genotypes in a DP system has bility and additional economic advantages compared the added complexity and expense of using livestock, knowledge of the benefits of using a DP production C.T. MacKown, USDA-ARS, Grazinglands Research Lab., 7207 W. system to select genotypes intended for DP is essential. Cheyenne St., El Reno, OK 73036; B.F. Carver, Dep. of Plant and The objective of our research was to compare fall forage Soil Sciences, 368 Ag Hall, Oklahoma State Univ., Stillwater, OK traits of bulk populations of wheat crosses selected from 74078. Received 3 Mar. 2004. *Corresponding author (cmackown@ grl.ars.usda.gov). GO and DP systems to evaluate the benefits of tailoring a wheat breeding program for DP wheat. Traits targeted Published in Crop Sci. 45:322–328 (2005). included shoot biomass, total N, and nitrate concentra© Crop Science Society of America 677 S. Segoe Rd., Madison, WI 53711 USA tion at the onset of fall grazing.