GRASS FORAGE QUALITY AND DIGESTION KINETICS AS INFLUENCED BY NITROGEN-FERTILIZATION AND MATURITY

Objectives were to assess the influence of N fertilization of reed can arygrass and timothy on fiber and N partitioning digestion kinetics an d on model-predicted quality. Four replicated field plots of each gras s received one of five levels of N fertilization (0, 67, 90, 135 and 2 69 kg of N/ha) and grasses were evaluated at first-cutting in 2 yr. Fe rtilization with N affected fiber composition quadratically both years . Rate of in vitro NDF digestion increased two fold when forages were fertilized with 269 versus 0 kg of N/ha, ranging from .041 to .087/h i n 1994 and from .047 to .078/h in 1995. Crude protein increased linear ly with increased N fertilization (from 9.9 to 21.7 % and from 11.9 to 22.3 % in 1994 and 1995, respectively). Neutral detergent insoluble f iber decreased from 26.5 to 18.0% and from 27.5 to 21.0% as N fertiliz ation increased from 0 to 269 kg of N/ha in 1994 and 1995, respectivel y. Because of higher total CP, reed canarygrass diets balanced with le ss soybean meal than timothy when fertilized with 0 and 90 kg of N/ha. With grasses fertilized with 28 kg of N/ha, however, CP in grasses ex ceeded requirements and more timothy could be used in the diet than re ed canarygrass. Although total CP was lower in timothy, neutral deterg ent insoluble protein was higher than In reed canarygrass. The Cornell Net Carbohydrate and Protein System model predicted forage species, h arvest and fertility management will result in differences in milk pro duction These factors need to be considered when making management dec isions.