Grass forage quality and digestion kinetics as influenced by nitrogen fertilization and maturity

Abstract

Objectives were to assess the influence of N fertilization of reed canary grass and timothy on fiber and N partitioning, digestion kinetics and on model-predicted quality. Four replicated field plots of each grass received one of five levels of N fertilization (0, 67, 90, 135 and 269 kg of N/ha) and grasses were evaluated at first-cutting in 2 yr. Fertilization 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 in 1994 and from .047 to ,078/h in 1995, Crude protein increased linearly 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 fiber decreased from 26.5 to 18.0% and from 27.5 to 21.0 % as N fertilization increased from 0 to 269 kg of N/ha in 1994 and 1995, respectively. Because of higher total CP, reed canary grass diets balanced with less soybean meal than timothy when fertilized with 0 and 90 kg of N/ha. With grasses fertilized with 269 kg of N/ha, however; CP in grasses exceeded requirements and more timothy could be used in the diet than reed canary grass. Although total CP was lower in timothy, neutral detergent insoluble protein was higher than in reed canary grass. The Cornell Net Carbohydrate and Protein System model predicted forage species, harvest and fertility management will result in differences in milk production. These factors need to be considered when making management decisions. © GSP, India.