Browsing Journal of Range Management, Volume 46, Number 3 (May 1993) by Subjects
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Decomposition of blue grama and rough fescue roots in prairie soilsThe mass of grass roots of blue grama (Bouteloua gracilis (HBK.) Lag. ex Steud) and rough fescue (Festuca campestris Rydb.) to a depth of 13 cm is similar but the carbon contents of their respective soils are quite different. The objective of the present study was to determine some of the physical and chemical changes of blue grama and rough fescue root masses during decomposition under both Brown (Mixed Prairie) and Black Chernozemic (Fescue Prairie) soil-forming conditions. Roots of each species in fine-mesh nylon bags were buried in the Ah horizon of both a Brown and a Black Chernozemic soil. Sixteen collections were made between November 1987 and June 1989 to determine diminution, loss of dry matter and gross energy, and changes in the concentration of carbon, nitrogen, methoxyl groups, alkaline-soluble organic acids and phenols, structural and nonstructural carbohydrates, lignin, and monosaccharides. Differences in substrate quality were only partially responsible for the increased decomposition of root mass in the Brown Chernozemic soil-forming environment. Comminution of root mass was significantly greater under the Mixed Prairie than under the Fescue Prairie conditions for both species. The nitrogen content of blue grama roots increased (from 1.17 to 1.56%) while that of rough fescue decreased (from 1.53 to 1.26%) significantly over the duration of the experiments at both sites. Methoxyl group content and energy levels were not useful parameters. Organic acid, phenols, and nonstructural carbohydrate contents decreased with time. Lignin concentration displayed a significant upward trend for both species (from 232 to 280 for blue grama and for 205 to 247 mg/g for rough fescue) in the Black Chernozemic soil only.
Influence of ruminally dispensed monensin and forage maturity on intake and digestionEight ruminally cannulated crossbred steers (average weight 336 kg) grazing native blue grama (Bouteloua gracilis [H.B.K.]) rangeland were used in a repeated measures design to evaluate effects of monensin ruminal delivery devices (MRDD) and forage phenology on ruminal digestion. Three periods were assessed: mid-August (Aug.), early October (Oct.), and mid-November (Nov.). One MRDD was placed in the reticulum of 4 steers via the ruminal cannula 21 days before each period. Intake was estimated using total fecal collections. Diet samples were collected using 3 esophageally fistulated steers. Ruminal fill was measured by ruminal evacuation; rate and extent of in situ ruminal neutral detergent fiber disappearance were estimated before ruminal evacuations. Ruminal passage rates, retention time, and apparent total tract organic matter digestibility were estimated using indigestible neutral detergent fiber. In vitro organic matter disappearance of esophageal masticate did not differ (P > .05) in Aug. and Oct. (average of 53.7%), but declined (P < .05) in Nov. (48.7%), whereas organic matter digestibility was greater (P < .10) in Aug. (62.3%) than in either Oct. (55.2%) or Nov. (53.9%). Release of monensin from the bolus (68 mg day-1) was less than expected (100 mg day-1). Intake, organic matter digestibility, ruminal passage rates, retention time, pH, and ammonia were not affected (P > .10) by MRDD. In situ neutral detergent fiber disappearance at 96 hours was decreased (P < .10) by MRDD (68 vs 65% for control and MRDD, respectively). As the grazing season progressed, intake declined (P < .10), whereas ruminal fill and retention time increased (P < .05), and passage rate of indigestible neutral detergent fiber decreased (P < .05). At 48 hours in situ neutral detergent fiber was greatest (P < .05) in Aug. and least (P < .05) in Nov.