How Does Plant Population Density Affect the Forage Yield of Eastern Gamagrass?

interval and that total forage production was higher for plots harvested at 6-wk compared with 4-wk intervals. Eastern gamagrass [Tripsacum dactyloides (L.) L.] is a perennial, The effects of plant population density on horticulwarm-season bunchgrass native to the Americas. Although much is tural and field crops is well established (Wade et al., known about the effects of fertilization and harvest frequency on the 1988; Boquet, 1990; Hintz and Fehr, 1990; Wade and yield of eastern gamagrass, information on the effects of plant density on yield is lacking. Our objectives were to investigate the effects of Douglas, 1990; Lege et al., 1993; Lauer, 1995; Cuomo plant population density on annual dry matter (DM) yield, vegetative et al., 1998; Cusicanqui and Lauer, 1999). In contrast, shoot density, and basal area of plant crowns of irrigated eastern very little is known about the effects of plant density gamagrass. Cumulative forage DM yield varied significantly with on the yield of native forage grasses or other forage year density interactions (P 0.01). Higher plant densities prospecies (Bolger and Meyer, 1983; Cooksley and Goward, duced greater DM yields with the highest sustained forage yields 1988; Graybill et al., 1991; Pinter et al., 1994; Jefferson obtained at a density of 4.8 plants m 2. Variation in number of vegetaand Kielly, 1998; Sanderson and Reed, 2000). For field tive shoots per square meter was attributed to year (P 0.05) and crops such as corn (Zea mays L.), sorghum [Sorghum density (P 0.01). Higher plant densities also had a greater number bicolor (L.) Moench], and soybean [Glycine max (L.) of vegetative shoots; however, plots with higher initial stand densities Merr.], grain yields are generally maximized by adreached equilibrium much faster than plots with lower stand densities. justing the planting densities to the moisture conditions Variation in crown area was associated to year density interactions (Jones and Johnson, 1991; Sanderson et al., 1996). (P 0.01). Mature shoots near the edge of the crown probably produce a greater number of tillers until an equilibrium is reached. Densely populated stands utilize available moisture and This is suggested by our data where the number of vegetative shoots nutrients more quickly than sparsely populated stands per plant increased with decreasing plant density. Most planting rec(Jones and Johnson, 1991). ommendations for eastern gamagrass call for seeding into wide rows. Plant morphology is also affected by plant density. These recommendations were developed to enhance seed production Skalova and Krahulec (1992) found that as plant density stands and facilitate the use of field equipment. Narrower row spacings increased, tiller numbers of Festuca rubra L. decreased. may facilitate stand establishment while increasing forage production Similarly, Hiernaux et al. (1994) found plant tillering early in the life of the stand. compensated for low plant density that resulted from drought or intense grazing. Most of the information available on the effects of plant density on forage quality E gamagrass is a highly productive and palatand feeding value is from tropical forage corn or forage able forage grass that can be grown throughout the sorghums (Pinter et al., 1994; Sanderson et al., 1996; Southern Plains and the eastern USA. The number of Cuomo et al., 1998; Cusicanqui and Lauer, 1999). hectares grown has increased during the past decade Understanding the growth and development of nawith renewed interest in its use for pasture production tive, warm-season grasses at varying population densiand soil conservation. The effects of harvest frequency ties will improve forage management, production, and and N fertilization of eastern gamagrass on yield is well utilization. The objectives of this study were to deterdocumented (Brejda et al., 1996, 1997); however, informine the effects of plant population density on the DM mation on the effects of plant density on yield is lacking. yield, vegetative shoot density, and basal area of plant Brejda et al. (1996) reported a curvilinear response in crowns of irrigated eastern gamagrass. forage production as N rate increased with yield peaking near 10 600 kg ha 1 with 224 kg N for plots harvested MATERIALS AND METHODS at 6-wk intervals at Elsberry, MO, and a linear response This study was conducted at the USDA-ARS, Southern in forage yield with forage production continuing to Plains Range Research Station, Woodward, OK (36 25 N, increase at the same N level at Clifton Hill, MO. They 99 24 W, elevation 615 m) on a Carey silt loam (Fine-silty, also reported that three or four harvests were possible mixed, superactive, thermic Typic Argiustolls). Plants of eastduring the growing season with a 4-wk harvest interval ern gamagrass accession WW-1000 were subdivided into raand that two or three harvests were possible with a mets consisting of a single shoot with root to ensure a uniform plant material for transplanting. Accession WW-1000 is a lo6-wk interval. They further reported that crude protein cally adapted strain of eastern gamagrass collected on the concentration of forage harvested at a 4-wk interval Southern Plains Range Research Station in 1971, and is similar averaged 131 g kg 1 compared with 97 g kg 1 for a 6-wk to other naturally occurring populations of eastern gamagrass found in western Oklahoma and the Texas panhandle. Ramets from this accession were transplanted in early March 1976 USDA-Agricultural Research Service, Southern Plains Range Reinto four blocks (replications) consisting of four variable sized search Station, 2000 18th Street, Woodward, OK 73801. Received 25 plots (treatments). Variable plot sizes were used to obtain the Nov. 2002. *Corresponding author ([email protected]). desired plant population densities. The treatments consisted Published in Crop Sci. 43:2206–2211 (2003).  Crop Science Society of America 677 S. Segoe Rd., Madison, WI 53711 USA Abbreviations: DM, dry matter.