Herbage Productivity and Botanical Composition of Hill Pasture as a Function of Clipping and Site Features
Complex topography and varied soil of hill-land pastures create microsite conditions that support an array of floristic associations and herbage production patterns. This complicates management for forage and livestock production because the seasonal distribution and quantity of forage vary. Our objective was to determine herbage production and floristic composition of a hill pasture as a function of site characteristics and canopy management. An existing 3-ha hill pasture watershed was oversown with white clover (Trifolium repens L.) and orchard-grass (Dactylis glomerata L.) and fertilized with reactive phosphate (PO 4 ) rock (PR). Replicated plots on each of four sites were clipped once (stockpiled), twice (hay harvest), or three times (long rotation) annually. Site had a significant impact on cumulative herbage production, whereas the influence of clipping was mixed. The least (1.9 Mg ha -1 ) amount of herbage production in a given season occurred on a northeast (NE)-facing site and the greatest (4.6 Mg ha -1 ) in a natural drainage area (ND) traversing the pasture. Herbage production increased by about 80% with overseeding and PR, but the relative ranking of production among sites stayed the same. Botanical composition was also strongly influenced by site, with velvetgrass (Holcus lanatus L.) predominating in ND and red fescue (Festuca rubra L.) occurring primarily on the NE site. The stockpiled treatments became dominated by grasses and weeds 4 yr after treatments were imposed, regardless of site, and were similar to the least productive site (NE-facing) in the pasture. Our results suggest that application of amendments to the more productive portions of a site are likely to have greater return.
INFLUENCE OF FUNGAL ENDOPHYTE INFECTION ON PLANT–SOIL FEEDBACK AND COMMUNITY INTERACTIONS
Interactions between plants and soil affect plant–plant interactions and community composition. Festuca arundinacea (tall fescue) is often infected with the mutualistic fungal endophyte Neotyphodium coenophialum. Infected (E+) F. arundinacea has been reported to inhibit soil pathogens, nematodes, and mycorrhizal fungi, and to have greater mineral uptake from the soil relative to uninfected (E−) F. arundinacea. In addition, endophyte presence may indirectly influence the soil by altering the plant–plant interactions and the composition of communities. Recent studies have shown that local plant species diversity was reduced in experimental field plots with E+ F. arundinacea compared to plots with E− plants. Endophyte-induced changes, direct or indirect, in biotic or abiotic soil properties could therefore affect subsequent plant growth. We investigated soil-mediated effects of E+ F. arundinacea on E+ and E− F. arundinacea, Trifolium repens, and Plantago lanceolata by growing each in soil collected from the ...
Effects of thyrotropin-releasing hormone and a thyrotropin releasing hormone analog on growth and selected plasma hormones in lambs.
An 8-wk growth trial was conducted to assess the effects of continuous infusion of thyrotropin-releasing hormone (TRH) and an active TRH analog less than Aad-His-Pro-NH2 (the less than Aad is L-pyro-alpha-aminoadipic acid) on growth trial performance, carcass composition and hormone profiles of growing lambs. Both drugs were infused at 600 micrograms X lamb -1 X d -1 with 16 lambs/treatment. Both TRH and less than Aad-His-Pro-NH2 decreased average daily gain (ADG; P less than .01) and increased feed conversion (FC; P less than .01) compared with saline infused controls. Average daily feed intake was not altered. Carcasses of lambs given TRH or less than Aad-His-Pro-NH2 contained fewer kilograms of moisture (P less than .05) and appeared to contain fewer kilograms of protein. Thyrotropin-releasing hormone and less than Aad-His-Pro-NH2 increased thyroid gland weights (P less than .05), but pituitary gland weights were not different. Plasma thyrotropin (TSH) concentrations were increased by both drugs compared with control lambs, peaking at 4 to 7 d after initiating infusion. However, by 14 d, TSH concentrations returned to control levels. Triiodothyronine (T3) and thyroxine (T4) were elevated by both drugs over the entire 8-wk trial, with peak levels reached at 10 d and maintained for the duration of the study. Both TRH and less than Aad-His-Pro-NH2 increased prolactin over the entire period. Growth hormone levels were not altered by either drug. The effects of less than Aad-His-Pro-NH2 infusion on growth trial performance, carcass composition and hormone profiles of growing lambs were very similar to TRH. The negative effects of TRH and less than Aad-His-Pro-NH2 infusion on ADG, FC and carcass protein appear to be the result of elevated T3 and T4 levels.