Forage Mixture Productivity and Botanical Composition in Pastures Grazed by Dairy Cattle

the plant diversity of natural grassland communities, some producers in the Northeast often plant complex Some producers believe that planting pastures to several forage mixtures of grasses and legumes (Tracy and Sanderson, species benefits sustainability of grazing systems. We conducted a grazing study to determine if forage species diversity in pastures affects 2000; Sanderson et al., 2001) because they believe that herbage productivity and weed invasion. One-hectare pastures were maintaining a highly diverse botanical composition in planted to four mixtures in August 2001 and then grazed with lactating pastures benefits persistence, yield stability, and prodairy cattle during 2002 and 2003. The mixtures were two species [orductivity. chardgrass (Dactylis glomerata L.) and white clover (Trifolium repens Perceived benefits from natural diversity have been L.)], three species [orchardgrass, white clover, and chicory (Cichorium linked to increased plant production and greater yield intybus L.)], six species [orchardgrass, tall fescue (Festuca arundinastability in response to disturbance (Minns et al., 2001). cea Schreb.), perennial ryegrass (Lolium perenne L.), red clover (TriThe proposed mechanisms behind these responses in natfolium pratense L.), birdsfoot trefoil (Lotus corniculatus L.), and ural grasslands include complementarity of resource use, chicory], and nine species [the six-species mixture plus white clover, facilitation, or a sampling effect (Sanderson et al., 2004). alfalfa (Medicago sativa L.), and bluegrass (Poa pratensis L.)]. When rainfall was plentiful (2003), there were no differences in herbage Early research on forage mixtures in the USA indiyield among the mixtures; all averaged 9800 kg ha 1 dry matter. During cated conflicting results. Clipped plot studies in Connec2002, which was dry, the two-species mixture produced less herbage ticut showed that increasing the number of grasses and than the other mixtures (4800 vs. 7600 kg ha 1 dry matter). The prolegumes in a mixture did not benefit herbage yield portion of nonsown species in the sward was lower for the sixand (Brown and Munsell, 1936). Grazing and clipping studnine-species mixtures than the two-and three-species mixtures, indiies under irrigation in Utah, however, indicated a posicating less weed invasion for these complex mixtures. Red clover and tive relationship between herbage yield and the number chicory proportions decreased by 80% after 2 yr, and orchardgrass of grasses and legumes in mixtures (Bateman and Keller, dominated in all pastures by May 2004. We conclude that planting a 1956). Recent work with forage mixtures in small plots mixture of grasses, legumes, and chicory will benefit herbage producdemonstrated small responses in herbage yield from tion during dry years and will reduce weed invasion for a few years after planting under management similar to ours. Producers would complex (9 to 15 species of grasses, legumes, and forbs) have to reestablish the chicory and legume components relatively versus simple (one grass and one legume) mixtures of frequently to maintain these benefits. forages (Tracy and Sanderson, 2004a; Deak et al., 2004). Research in Ontario, Canada indicated that pastures planted to a complex mixture of six cool-season grasses I the northeastern USA, grazing land accounts for and three legumes maintained this complexity and inabout 3.5 million ha (USDA-NRCS, 2002) and concreased in productivity after 3 yr of intensive grazing tributes substantially to the agricultural economy. Formanagement (Clark, 2001). In New Zealand, pastures age–livestock operations in this region are shifting from seeded with a mixture of 18 to 26 species of cool-season using mainly confinement and stored forages to using grasses and pasture herbs [chicory and plantain (Planintensively managed pastures as the primary forage base tago lanceolata L.)] yielded more herbage under sheep (Rotz and Cropper, 1998; Sanderson et al., 2001). Reagrazing than did simple perennial ryegrass–white clover sons for the change include (i) lower production costs mixtures (Ruz-Jerez et al., 1991; Daly et al., 1996). The in(Ford and Musser, 1998), (ii) improved animal health creased production resulted mainly from chicory growth (Goldberg et al., 1992; Washburn et al., 2002), and (iii) during the summer. a perceived better quality of life for the farm family Highly diverse grassland ecosystems may be more re(Jackson-Smith et al., 1996). sistant to invasion by weeds and pests because of (i) a The role of plant species diversity or forage mixture highly competitive environment created by a greater complexity in pastures has not been well explored (Sanuse of resources or (ii) the inclusion of a few highly derson et al., 2004). Nonetheless, taking their cue from productive species, which dominate and preclude invasion (Kennedy et al., 2002). Smother crops are an agronomic example of the latter mechanism. Limited eviM.A. Sanderson, K.J. Soder, K.D. Klement, R.H. Skinner, and S.C. Goslee, USDA-ARS, Pasture Syst. and Watershed Management Res. dence points to both mechanisms operating in pastures. Unit, Bldg. 3702, Curtin Rd., University Park, PA, 16802-3702 USA; For example, weed abundance was negatively related to and L.D. Muller, Dep. of Dairy and Animal Science, The Pennsylvania the evenness (i.e., the relative abundance and distribuState Univ., University Park, PA, 16802 USA. Received 31 Dec. 2004. tion of species) of forage species in both experimental *Corresponding author ([email protected]). pasture mixtures and in pasture surveys of plant spePublished in Agron. J. 97:1465–1471 (2005). cies diversity on farms (Tracy and Sanderson, 2004a, Pasture Management 2004b). Species composition of forage mixtures also afdoi:10.2134/agronj2005.0032 fected weed abundance: mixtures based on tall fescue © American Society of Agronomy 677 S. Segoe Rd., Madison, WI 53711 USA had fewer weeds in the soil seed bank and aboveground 1465 Published online September 19, 2005