ALFALFA COMPOSITION AND IN-SACCO FIBER AND PROTEIN DISAPPEARANCE AS INFLUENCED BY NITROGEN APPLICATION

Nitrogen (0, 112, 224, 336 kg of N as ammonium nitrate/ha) was applied to field plots of established alfalfa (Medicago sativa L.) to evaluat e its effect on forage quality. Two first-growth cuttings (bud stage; 1 wk apart) were harvested beginning in May. Alfalfa fertilized with 3 36 kg N/ha had slightly lower neutral detergent fiber (NDF) than alfal fa fertilized with 0 kg N/ha (32% vs. 33% NDF). Nitrate, crude protein , soluble crude protein (dry matter basis) and crude protein solubilit y increased with increased N fertilization. As expected, the Later cut ting 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 d ate and level of fat in cow diet on dry matter disappearance and N dis appearance. High fat (7%) resulted in lower dry matter disappearance t han a low fat (3%) diet at 24 h (79.4% vs. 84.1%). Harvest date did no t influence measured parameters. Crude protein solubility and nitrates both increased with increased N application. This increase in CP incr eased N disappearance in the rumen, as measured by a second in sacco s tudy. This could result in increased problems with utilization of alfa lfa nitrogen by ruminants. The effect of N application on forage quali ty was negligible after the first harvest, however, suggesting that mo derate manure application to established alfalfa fields may be an acce ptable practice from a forage quality standpoint.