Doctoral Dissertations

Date of Award

3-1982

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Plant, Soil and Environmental Sciences

Major Professor

Henry A. Fribourg

Committee Members

J. B. McLaren, J. H. Reynolds, J. W. Holloway

Abstract

A beef backgrounding pasture experiment was conducted on a Typic Hapludalfs soil to measure forage and steer production from seven (1.2-ha/ experimental unit) pasture treatments: (1) 'Midland' bermudagrass (Cynodon dactyl on (L.) Pers.) + Ladino clover (Trifolium repens L.) [Midland + clover]; (2) Midland + 224 kg N/ha [Midland + N]; (3) 0.4 ha Midland + N-0.8 ha of tall fescue (Festuca arundinacea Schreb.) + N [Midland (0.4 ha)-fescue (0.8 ha)]; (4) Midland + fescue + N [Midland + fescue]; (5) Common bermudagrass (Cynodon dactyl on var. dactyl on) + 224 kg N/ha [Common + N]; (6) Fescue + clover; and (7) Orchardgrass (Dactylis glomerata L.) + clover [Ore. + clover]. The pastures were replicated twice and grazed with a modified put-and-take system. Yearling steers weighing about 230 kg in spring grazed up to 150 days. Forage and steer data were taken every three weeks. A species composition index (SCI) was developed to describe each pasture each time with a unique symbol; it was a sensitive tool for characterizing dynamically changing pasture compositions. Forage consumption was 80% or more of estimated growth, which was 4000 to 8300 kg/ha. Crude protein was sufficient to meet minimum requirements for growing steers. Fescue or clover, which were successfully introduced and maintained in Midland sods, extended the grazing season, and the resulting combinations produced more forage than Midland + N alone. Stocking rates ranged from four to seven steers/ha. Average daily gains (ADG) were about 475 to 575 g for all treatments except for Ore. + clover (825 g). Productivity ranged between 520 grazing days/ha/season for Ore. + clover to 1190 for Midland + fescue; most were 730 to 880 grazing days/ha. Daily forage dry matter intake was five to seven kg/steer in all pastures, with intake efficiencies of 9 to 13 kg/kg gain. Beef production was 390, 412, 456, 485, 505, 515, and 720 kg/ha for Fescue + clover. Common + N, Midland (0.4 ha)-fescue (0.8 ha). Midland + clover. Ore. + clover. Midland + N, and Midland + fescue, respectively. Models were developed to identify concomitant variables such as stocking rate/21-day sampling period, season (spring or summer), year, days/period, crude protein, and precipitation in addition to the classification variables "treatments" or SCI, that could account for variability in the dependent variables. When "treatments" was entered in the model, R²'s of 0.26, 0.43, 0.58, and 0.44 were obtained for forage growth, forage consumption, ADG and beef production, respectively; when SCI was used, they were 0.40, 0.52, 0.68,

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