Influence due Niveau de Fertilization Azotee sur la Degradabilite de L\u27Azote de la Fetuque Elevee Recoltee en Vert

Il est connu que la fertilisation azotee ameliore non seule­ment la biomasse produite mais aussi la teneur en azote de la plante; cependant certains auteurs la soup9onnent de reduire le flux d\u27azote duodenal (Armstrong, 1974). Cette diminution de la valeur azotee reelle pourrait s\u27expliquer par la baisse des syntheses de proteines microbiennes et/ou !\u27augmentation de la degradation ruminale des proteines de l\u27herbe. Dans ce travail, l\u27effet de 2 niveaux de fertilisation azotee, appliques sur 4 cycles successifs d\u27une fetuque, sur la degradabilite de l\u27azote de la plante verte a ete etudie par 3 methodes differentes ; de plus l\u27incidence du stade vegetatif et l\u27effet remanent de la fertilisa­tion anterieure out ete precises Sur le 4e cycle

Bridge Load Posting Based on Load Testing

AASHTO’s Manual for Bridge Evaluation (MBE) provides guidance for analytically evaluating bridge capacity based on available design information and the results of field inspections. This analysis results in a rating factor (RF), which quantifies a bridge’s safe load carrying capacity. RF accuracy, however, depends on the availability of information about structural details and material properties. As such, load rating bridges without design plans is difficult as field inspections alone often cannot provide enough information to perform detailed analysis. In many instances this means that a bridge would possess a substandard rating factor (RF \u3c 1.0) simply due to the conservative assumptions required to perform traditional analysis. The most effective method for safely modifying such conservative theoretical rating factors is through load testing. Load testing measures actual bridge behavior and, for most bridges in good health, finds an increase in load rating is justified. This project utilized load testing to load rate 14 bridges in Kentucky that lack structural plans. Researchers first determined theoretical ratings using MBE-prescribed methods. For information typically taken from design plans, but which could not be measured directly, data-backed methods for making conservative assumptions were developed. For most bridges included in the study, theoretical rating factors alone suggested load postings were necessary. Load testing was then carried out utilizing tandem rear-axle dump trucks with measured axle weights. Multiple single-lane load cases were selected to maximize the effects being rated. Strain data were collected in real time using a wireless reusable strain gage system. Using these data, researchers computed a field test adjustment factor using MBE methods which directly modified the calculated theoretical RFs. Ultimately, load testing provided sufficient evidence to safely recommend that load postings were not necessary for any bridges in this study

Factors Affecting the Productivity of Elephant Grass

Elephant grass (Pennisetum purpureum Schumach) is a highly productive and palatable fodder which is widely grown in the tropics (Bogdan, 1977). Optimum utilisation of its production potential is, however, limited by management factors which are associated with plant form and growth habit (Horrell and Tiley, 1970). These factors were studied in a series of trials at Kawanda Research Station, Kampala, Uganda (0°27\u27N, 32°30\u27E). A summary of the princi­ pal results is given

Estimation of Pasture Intake in Grazing Ewes, Using the Alkanes of Plant Cuticular Waxes

Herbage intake in grazing animals is commonly estimated from faecal dry matter output, calculated from the dilution of orally-administered chromium sesquioxide (Cr203), and an in vitro estimate of herbage digestibility (e.g., Freer et al. 1988). A major disadvantage of this approach is that a single digesti­bility value is ultimately applied to all the animals in a group, despite the fact that both the level of intake of individual ani­mals and the consumption of supplement can alter herbage digestibility (Waite et al. 1964). More recently, Mayes et al.(1986) obtained accrurate estimates of known herbage, from a combination of the faecal levels of the n-hydrocarbons (alkanes) of plant cuticular waxes (predominantly odd­numbered carbon chain length) and those of orally-admini­stered synthetic alkanes (even-numbered chain lengths). Neither type of alkane is wholly indigestible but, since alkanes of adjacent chain length have very similar faecal recoveries, the errors arising from incomplete recoveries cancel out in the cal­culcation of intake (Mayes et al. 1986). A major advantage of this method is that it reflects the digestibility in individual animals. It is thus well suited to grazing situations where levels of intake may differ between treatments or where supplements are used in some treatments. In this paper, we report the results of a comparison of these two methods for estimating herbage intake, conducted with grazing ewes

Grazing Management Effects on Perennial Ryegrass and White Clover Triller Populations

Pasture grazing managements have clearly identifiable effects on plant morphology, density and species composition. Typ­ically, swards grazed continuously by sheep have relatively high populations of relatively small perennial ryegrass tillers while rotationally grazed swards contain rather fewer large/ tillers (Chapman and Clark 1984, Suckling 1959, Mitchelle and Glen­day 1958, Collet et al., 1981). Generally, more severe defoli­ations are associated with greater tiller densities (Davies 1977). Management induced increases in tiller populations of per­ennial pastures are possible because plants tiller freely when competition for light is reduced by herbage removal (Hunt and Field 1978). If left undisturbed, tiller density is finally deter­mined by self-thinning and tiller size in accordance with the 3/2 power law (Kays and Harper 1974). Where intense competition for light does occur, such as in infrequently defoliated swards in spring (Ong 1978b), reductions in population density are achieved at the expense of the smallest tillers, they being the first to die (Ong 1978a). Studies of the interaction between grazing management and tiller dynamics, must focus on differences in rates of tiller pro­duction and loss as the initial cause of divergence in tiller den­sity. Parsons et al. (1984) suggest higher tiller densities occur in continuously stocked swards because the faster growing tillers wich could potentially eliminate their slower growing neighbours are inhibited from doing so because the faster growing tillers are the ones defoliated most frequently. This paper reports on a study in which the rates of pro­duction and loss of grass tiller and clover buds under three sheep grazing management systems was closely monitored with the objective of identify mechanisms whereby grazing manage­ment determines population density

Managing Woody Weeds in Grazing Ecosystems: Application for Tropical Woodlands of North-eastern Australia

Shrub invasion of tropical woodlands is reducing the viability of native ecosystems as well as the livestock industry, After shrub invasion, forage supply is reduced and over-grazing and soil erosion are exacerbated. We propose a non-equilibrium model of the system and use that model to develop hypotheses and design experiments to test both competition- and disturbance-based management regimes. This model proposes that disturbance in the form of burning is the primary limiting factor in excluding and limiting shrub seedling establishment and suggests that management decisions focus on maintaining adequate herbaceous biomass for a burning regime that limits woody plant success

Methods for the Establishment of Leucaena leucocoephala in Cuba

Studies in tropical and sub-tropical regions of the world on the factors influencing the establishment and early manage­ment of legume swards as pure cultures have not been carried out integrally. Thus, the objective of the present study was to define the best options of the main components so as to develop a technology for establishing Leucaena leucocephala under our conditions