SWARD DYNAMICS AND HERBAGE NUTRITIONAL-VALUE OF ALFALFA-RYEGRASS MIXTURES

No grass species has proven to be well suited as a companion grass in binary mixtures with alfalfa, Medicago sativa L., over a wide range of environments and management practices. Two trials were conducted with alfalfa and perennial ryegrass, Lolium perenne L., as binary mixtures and monocultures in Pennsylvania, USA (41-degrees-N, 77-degrees 30'W) to determine the influence of seeding rate and phenological development and tillering potential of ryegrass on sward dynamics and herbage nutritional value. The experiment was seeded on Hagerstown silt loam (fine, mixed, mesic Typic Hapludalfs) soil in August 1983 and 1984 to determine consistency of sward dynamics of stands seeded in different years. Field plots were harvested in late May and after 35-d intervals in summer, and 45 d in fall. Near infrared reflectance spectroscopy was used to estimate botanical composition of the mixtures. Nitrogen concentration and in vitro dry matter disappearance determinations were made on freeze-dried herbage for 2 yr from one of the two trials. Botanical composition of alfalfa-perennial ryegrass mixtures was influenced more by ryegrass seeding rate than by alfalfa seeding rate. The influence of alfalfa and ryegrass seeding rates on botanical composition was particularly large during stand establishment and the first crop year. Alfalfa became the dominant species within 1 yr in all mixtures in both trials even when conditions heavily favored ryegrass during stand establishment. Annual yield of digestible dry matter was maximized at 9.9 Mg ha-1 when alfalfa and perennial ryegrass were seeded at approximately 15 and 11 kg ha-1, respectively. Weed content of the mixtures was inversely related to seeding rate of ryegrass.