Alfalfa Composition and in sacco Fiber and Protein Disappearance as Influenced by Nitrogen Application

Abstract

Cherney, D.J.R., Cherney, J.H. and Siciliano-Jones, J. 1995. Alfalfa composition and in sacco fiber and protein disappearance as influenced by nitrogen application. J. Appl. Anim. Res. 8:105–119.

Nitrogen (0, 112, 224, 336 kg of N as ammonium nitrate/ha) was applied to field plots of established alfalfa (Medicago sativa L.) to evaluate its effect on forage quality. Two first-growth cuttings (bud stage; 1 wk apart) were harvested beginning in May. Alfalfa fertilized with 336 kg N/ha had slightly lower neutral detergent fiber (NDF) than alfalfa fertilized with 0 kg N/ha (32% vs. 33% NDF). Nitrate, crude protein, soluble crude protein (dry matter basis) and crude protein solubility increased with increased N fertilization. As expected, the later cutting of alfalfa was higher in NDF and lignin and lower in nitrate and crude protein (CP). In another study, alfalfa was ruminally incubated in nylon bags to determine the influence of N fertilization, harvest date and level of fat in cow diet on dry matter disappearance and N disappearance. High fat (7%) resulted in lower dry matter disappearance than a low fat (3%) diet at 24 h (79.4% vs. 84.1%). Harvest date did not influence measured parameters. Crude protein solubility and nitrates both increased with increased N application. This increase in CP increased N disappearance in the rumen, as measured by a second in sacco study. This could result in increased problems with utilization of alfalfa nitrogen by ruminants. The effect of N application on forage quality was negligible after the first harvest, however, suggesting that moderate manure application to established alfalfa fields may be an acceptable practice from a forage quality standpoint.

Key words:

• Medicago sativa L.
• fiber
• protein
• nitrogen fertilization