| Alfalfa is a high quality forage and also provides a nitrogen (N) benefit to following nonlegume crops. This study examined growth habit and harvest schedule effects on in vitro digestibility of forage; yield and N accumulation of forage, stubble, crowns, and roots; and structural polysaccharide composition and in vitro digestibility of leaves and stems.;Nonwinter-dormant alfalfa, treated as an annual crop, approached the root, crown, and stubble N yields of 2-year-old winter-dormant cultivars. Seasonal forage yields were about half those of established winter-dormant alfalfa.;Leaves contained lower concentrations of cell walls than stems. In leaves, little change in cell wall concentration or composition occurred with increasing maturity. Leaf cell walls contained greater concentrations of nonglucose sugars--especially arabinose and galactose--than stems. Cell walls of stems of both erect and semiprostrate cultivars decreased in cellulose, increased in lignin, and remained constant in hemicellulose concentrations with maturation. Total cell wall neutral sugars in alfalfa stems increased from 300 to 450 g kg('-1) dry matter from the vegetative to early-pod stage. Concentrations of glucose and xylose increased, arabinose and galactose decreased, and mannose and rhamnose remained constant in the structural polysaccharides. In alfalfa stems, galactose was most extensively degraded by rumen microorganisms (73%), followed by arabinose (68%), rhamnose (57%), glucose (54%), mannose (46%), and xylose (24%). Thus, cell walls of leaves and immature stems contained greater concentrations of easily digested sugars than mature stems.;Based on results of this study, harvest schedule and cultivar (but not necessarily growth habit) affect forage quality and N distribution within the plant. Growth habit and especially maturity affect cell wall composition which is directly related to quality.;Six cultivars varying in growth habit were harvested each time they reached the bud, first-flower, mid-flower, or early-pod stage of development. With winter-dormant cultivars, greatest 2-year forage, root, crown, and in vitro digestible dry matter yields were obtained by using the mid-flower cutting schedule. Greatest 2-year N yields of forage, crowns, and roots were also obtained under the mid-flower management. Differences among cultivars for these traits were also observed. |
