Experiments were conducted to investigate the fermentation characteristics and nutritional value of mixtures containing different proportions of alfalfa (Medicago sativa L.) and wheat (Triticum aestivum L.) straw ensiled with and without molasses, microbial inoculant and molasses + microbial inoculant. In experiment 1, chopped alfalfa harvested at 1/10 bloom and chopped wheat straw were ensiled in the following proportions (DM basis): 0:100, 25:75, 50:50, 75:25, 100:0, 0:100 (urea-treated), with O and 5% dry molasses, and 0 and .1% microbial inoculant (Lactobaci]lus plantarum and Streptococcus faecium) in a 6 x 2 x 2 completely randomized design with a factorial arrangement. Each mixture was ensiled in 3.8-liter cardboard containers double lined with polyethylene. The pH values for the ensiled mixtures of 0:100, 25:75, 50:50, 75:25 and 100:0 alfalfa:straw without additives were 4.70, 4.76, 4.65, 4.76 and 4.82, respectively. Urea treatment of the 0:100 mixture (wheat straw) increased (P < .01) pH to 8.84. Overall lower pH (P < .01) occurred when molasses was added, compared to untreated and inoculated silages. Lactic acid concentration decreased (P < .01) linearly with decreased level of alfalfa, over all additives. Molasses increased (P < .01) lactic acid concentration. Overall, water soluble carbohydrates (WSC) in pre-ensiled mixtures increased (P < .01) linearly with increases in alfalfa. The WSC decreased (P < .01) after ensiling. Microbial inoculant did not affect pH or lactic acid content in the silages. In vitro dry matter digestibility (IVDMD) increased (P < .01) linearly with level of alfalfa, and molasses increased (P < .01) IVDMD. In experiment 2, chopped alfalfa (1/10 bloom, third cutting) and wheat straw were ensiled in the following respective proportions (DM basis): 0:100, 25:75, 50:50, 75:25, 100:0, 100:0 + 5% dry molasses, and 0:100 (urea-treated) in 210-liter metal drums double lined with .08 mm polyethylene bags. Increased proportions of wheat straw to alfalfa increased (P < .01) DM content and lactic acid concentration, and decreased pH and total VFA content. The CP, Ca, P, Mg and K contents decreased (P < .01) with increases in wheat straw. Addition of molasses to alfalfa increased (P < .01) WSC and lactic acid, and decreased (P < .01) pH and total VFA. Urea treatment of wheat straw increased (P < .01) pH and acetic acid, and decreased (P < .01) lactic acid, compared to untreated wheat straw. The NDF (P < .05) and hemicellulose (P < .01) were decreased with urea treatment. Two metabolism trials were conducted, each with 21 crossbred wethers. The diets were alfalfa and wheat straw silages made in 210-liter metal drums described above. Wheat straw ensiled alone was supplemented with soybean meal because of insufficient consumption when the straw was fed alone. Linear increases (P < .01) in DM, OM, and CP digestibilities were observed with increased level of alfalfa. Adding molasses increased (P < .05) DM digestibility. A linear increase (P < .01) in N retention was observed with increasing alfalfa level. Ruminal NH₃-N and blood urea-N increased (P < .01) with increased proportion of alfalfa. Feeding urea-treated straw increased (P < .01) ruminal NH₃-N and blood urea-N, compared to untreated wheat straw. A palatability trial was conducted with 42 sheep fed the same diets as in the metabolism trials. Daily DM intake increased linearly (P < .01) with increased proportion of alfalfa. It is concluded that ensiling cereal crop residues with leguminous forage has potential in improving fermentation characteristics and nutritional value of alfalfa silage and improving the nutritional value and utilization of cereal crop residues. / Ph. D.