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.
Identifying traits to improve the nitrogen economy of wheat: Recent advances and future prospects
Nitrogen fertilizer represents a significant cost of production for the grower and may also have environmental impacts through nitrate leaching, use of fossil fuels for manufacture and application, and N2O emissions associated with denitrification. The development of N-efficient cultivars will be of economic benefit to farmers and will help to reduce environmental contamination associated with excessive inputs of N fertilizers. The physiological, metabolic and physio-chemico processes that may contribute to high N-use efficiency (NUE) and reduced N fertilizer inputs while maintaining an acceptable yield are reviewed and the prospects for application in breeding programs discussed. Promising N management strategies for high NUE are also considered. Traits operating from the cellular to the whole-crop scale, including root traits, nitrate assimilation, N partitioning, leaf and canopy photosynthesis, senescence, grain N remobilization and grain protein content and composition, are discussed in relation to their optimization in both feed and bread-making cultivars. Promising traits for selection by breeders to increase NUE are identified, and approaches for their integration at the whole plant level discussed. It is concluded that: (i) increased root length density (RLD) at depth, (ii) a high capacity for N accumulation in the stem, potentially associated with a high maximum N-uptake rate, (iii) low leaf lamina N concentration, (iv) more efficient post-anthesis remobilization of N from stems to grain, but less efficient remobilization of N from leaves to grain, both potentially associated with delayed senescence, and (v) a reduced grain N concentration may be of particular value for increasing NUE in feed wheat cultivars; and (vi) for bread-making cultivars, high NUE may be associated with high capacities for uptake and assimilation of N, with high post-anthesis N remobilization efficiency and/or specific grain protein composition.
Pasteurella haemolytica serotype 1 colonization of the nasal passages of virus-infected calves.
Nasal passages of calves with a virus-induced respiratory tract disease became colonized by Pasteurella haemolytica serotype 1 after they were inoculated intranasally with P haemolytica. Inoculation with infectious bovine rhinotracheitis virus caused a more severe clinical illness and resulted in a greater degree of colonization with P haemolytica than developed after inoculation with parainfluenza-3 virus. Nasal passages of parainfluenza-3 virus-inoculated calves were colonized to a greater degree with P haemolytica than were those of healthy, nonstressed calves. Calves were susceptible to P haemolytica colonization during or shortly after virus-induced illness, even though they had been previously exposed to P haemolytica and had serum antibody and nasal secretion antibody to P haemolytica.