Ruminal nitrogen disappearance from sod-seeded cereal grain forages in Northern Arkansas

Wheat (Triticum aestivum L.), oat (Avena sativa a L.) and rye (Secale cerea le L.) were overseeded into a dormant bermudagrass (Cynodon dactylon IL.) P ers.) sod and harvested on six dates throughout the spring. Plant growth st age was documented for each forage on each harvest date, and harvested fora ges were subsequently evaluated for forage quality characteristics. Four ru minally cannulated steers were used to evaluate disappearance kinetics of n itrogen (N) by an in situ method, All forages had high concentrations of N (greater than or equal to 31.1 g kg(-1) DM) throughout harvest dates in Mar ch. By 15 April, rye had reached a substantially more advanced growth stage than either wheat or oat. This trait, coupled with the concurrent taller g rowth habit, caused concentrations of N in rye to decline (P < 0.05) rapidl y between the 24 March and 4 May harvest dates. The effective ruminal disap pearance of N remained high (<greater than or equal to>790 g kg(-1) N) for all forages harvested through mid-April, thereby indicating that these cere al-grain forages exhibit the same characteristics of high N disappearance a nd low potential ruminal escape that are commonly observed in other high-qu ality cool season grasses harvested at similar growth stages. The effective disappearance of N reached a minimum (P < 0.05) for all forages immediatel y before grain fill. Generally, substantial increases (P < 0.05) in effecti ve ruminal disappearance of N were observed as these forages partitioned N into the filling grain head. Fractional rates of N disappearance for wheat and rye were extremely rapid (greater than or equal to0.383 h(-1)) during g rain fill. However, rye also exhibited an extremely rapid disappearance rat e (0.548 h-l) immediately prior to the onset of grain fill that was not obs erved for wheat (0.085 h(-1)) at an identical growth stage. Parameters asso ciated with disappearance kinetics can be related to growth stage at harves t by linear and polynomial regression techniques, although the best fit mod el was dependent on forage type. (C) 2001 Elsevier Science B.V. All rights reserved.