ABSTRACT
Summary Two experiments were conducted with lactating Holstein cows to study the effects of different levels of nitrogen fertilizer (urea) on annual pasture: experiment 1, oats (Avena byzantina K. Koch) and ryegrass (Lolium multiflorum Lam.); experiment 2, millet (Pennisetum americanum [L.] Leche). Base fertilizer (8-28-18) was applied, and at the five-leaf stage three levels of nitrogen (N) (75, 150, and 225 kg/ha) were applied. The millet pasture followed the oat + ryegrass pasture, with the N treatments being maintained in the same areas. Two ha were planted for each treatment (total, 6 ha). In experiment 1, twelve lactating cows were randomly assigned to one of the three oat + ryegrass N treatments in various sequences (treatments a, b, and c) according to Lucas' “incomplete block switch back designs” for an 84-day trial. Each cow was offered 1 kg ration (16 % crude protein [CP])/3.5 kg of milk produced. Average milk production (kg), percentage of milk fat (MF), percentage of solids not fat (SNF), percentage of protein, and body weight (kg) were 11.3 kg, 3.7%, 8.1%, 3.3%, and 476 kg; 11.2 kg, 3.9%, 8.2%, 3.4%, and 481 kg; and 11.4 kg, 3.5%, 8.2%, 3.3%, and 490 kg for treatments a, b, and c, respectively. No significant (P = 0.05) differences were observed among treatments. Average pasture dry-matter availability/treatment during the trial was 2,900, 3,000, and 3,450 kg/ha/period for treatments a, b, and c, respectively. In experiment 2, twelve lactating cows, randomly assigned to one of the three millet-nitrogen fertilizer sequences according to Lucas' “incomplete block switch back designs,” served as tester cows. Pasture pressure was adjusted according to pasture availability with other lactating cows on a put-and-take basis. The trial was 63 days in duration. One kg of feed (16% CP) was offered/3.5 kg of milk produced. Average milk production, percentage of MF, percentage of SNF, percentage of protein, and weight were 11.1 kg, 3.6%, 7.72%, 2.93%, and 462 kg; 11.1 kg, 3.7%, 7.65%, 2.96%, and 457 kg; 11.2 kg, 3.2%, 7.8%, 2.5%, and 454 kg, respectively, for treatments a, b, and c. No significant differences were observed for these parameters, but in fat-corrected milk produced/cow, treatments a and b were superior to treatment c. Stocking rates/ha, milk production/ha, and pasture dry-matter availability/period were two cows, 1,350 kg, and 2,297 kg; three cows, 2,016 kg, and 3,734 kg; and five cows, 3,712 kg, and 4,836 kg for treatments a, b, and c, respectively. Treatment c was different from a and b at P < 0.01 for production/ha.
