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The objective with this experiment was to evaluate doses of 25-hydroxy-vitamin-D3 on average daily gain (ADG), dry matter intake (DMI), feed efficiency (F:G) and dressing percentage (DP) in finishing beef cattle. A total of 120 Nellore bulls (IBW = 375 ± 24 kg) distributed in 24 pen (5 animals/pen) were used in a randomized complete block design (8 pens/treatment). The dietary treatments were: 1) control (CON): no supplementation of 25-hydroxy-vitamin-D3, 2) HyD1: 25-hydroxy-vitamin-D3 supplementation at 1 mg/animal/d and 3) HyD3: 25-hydroxy-vitamin-D3 supplementation at 3 mg/animal/d. The basal diet was formulated to meet the requirements of finishing bulls to a ADG of 1.6 kg (Level 2 Nutrition System, Fox et al., 2004) and it was composed of 13% forage and 87% concentrate (DM basis). The animals were fed twice a day at 08:00 (40% of the total) and 15:00 (60% of the total). The pens were fully covered, protecting feed from the sun and rain, with good air circulation. At the beginning and end of the experimental period the animals were weighed without fasting for two consecutive days. The initial and final body weight was calculated by the average of the two days discounting 4% to obtain the lean weight. Statistical analysis was performed using the PROC MIXED procedure of SAS (2003) and means comparison evaluated by Tukey test at 10% probability. HyD supplementation did not change the final body weight (513.0 kg), ADG (1.43 kg/d), DMI (9.8 kg/d) and FE (0.145) (P > 0.10). Nevertheless, feeding HyD at 1 mg/d increased the dressing percentage of the animals compared to the control group (56,46 vs 55,92%; P = 0.063). In conclusion, HyD supplementation can be used as a tool to increase carcass yield in finishing cattle. Key Words

Certains experts ont proposé des thèmes de recherche complémentaires dans le cadre de réponses à des appels d’offres divers. Deux réseaux de recherche sont également proposés dans les « conclusions et recommandations » du rapport. Utilisation d’indicateurs pour le suivi du cycle culture/jachère et des effets des aménagements L’identification et la mise au point d’outils pratiques et simples d’emploi, permettant de caractériser l’état des ressources et du fonctionnement des différents stades d...

Le cycle culture-jachere est perturbe aujourd’hui par l’accroissement de la pression demographique et de la demande en terre. Les durees de jachere se sont raccourcies, laissant envisager a terme la disparition de cette pratique. Des methodes de substitution a la jachere ont ete avancees.L’objectif du « projet Jachere » (1994-2003) etait de realiser un programme d’etude, d’amelioration et de gestion de la jachere au niveau de terroirs villageois dans des pays d’Afrique tropicale. Il s’agissait d’inserer le cycle culture-jachere, ou les modes de substitution a la jachere lorsqu’elle a disparu, dans une strategie de developpement durable.Les resultats du projet Jachere ont fait l’objet de nombreuses publications scientifiques et techniques.Une « expertise collegiale » a ete entreprise pour degager les resultats susceptibles d’etre transferes en milieu paysan et pour examiner les conditions de ce transfert.

The purpose of this study was to characterize and quantify the degradation of Vertisols of savannas in Northern Cameroon. The work was carried out in a region with mean annual rainfall of 800 mm. It is a climate with 9 months theoretical drought and one raining season. The area is heavily populated and farmers use fallow to rejuvenate the soil. The post-cultural savannas (fallows) are subjected to fire, intensive grazing and cutting of fire wood. Three soil types at different stages of degradation were subjected to a study of their soil moisture regime including quantification of runoff during a three-year period. Physico-chemical characteristics are discussed, as well as variations in water reserves as a function of stages of degradation. Maximum wetting front varied from 30 to 80 cm. The most degraded soil lacked plant available moisture for 10 months as compared to 5 months for the least degraded. A model is presented of the dynamic relationships that may exist among the stages of degradation of these Vertisols. Key words: Savanna, Vertisol, water regime, degradation, soil dynamics

Five sympatric species of perennial pasture plants were studied in monospecific plots at an experimental site in the arid zone of southern Tunisia. For one year following establishment, irrigation was supplied monthly to test plots so as to complement natural precipitation and simulate an “optimum”; rain year (250 mm of precipitation occurring, evenly distributed, between September and April). In addition to hydrometric fluctuations in the upper soil layers, growth rate and phenological activity were monitored for all species (Cenchrus ciliaris, Digitaria commutata, Stipa lagascae (Poaceae), Argyrolobium uniflorum (Fabaceae) and Plantago albicans (Plantaginaceae)). Overall growth rate and foliar extension measurements revealed differential water use efficiency, phenology, and response to water stress in the species studied. C. ciliaris and D. commutata were the most efficient in their use of water. The former, a C4 grass species of paleo‐tropical origin, was primarily active in spring and autumn....

The present work describes a procedure based on the knowledge of the sand structure morphology, the sand mobility, the characteristics of the substrata underlying the sand accumulations and the vegetation (present and potential). It makes zone identification possible in a region where sand dune fixation is necessary. Its purpose is to allow an optimization (efficiency and cost) of the fight undertaken for the sand dune fixation in arid zones. The procedure is applied to an identified situation in southern Tunisia and gives some possible treatments among the most appropriate for each zone.

This work, carried out in the pre-Saharan region of Tunisia, was designed to investigate the changing characteristics of sandy steppe during its progressive invasion by wind-borne sand from disturbed neighbouring zones (regressive evolution). In addition, the development of the vegetation in such regions after the disturbance had ceased has been determined (progressive evolution). The method consisted of studying differences in the main perennial species in the presence of mobile sand, in order to establish whether these species show special adaptations to the mobility of the sand and their role in sand fixation. Only two species show ability to tolerate sand accumulation and are thereby able to fix drifting sand. These are Rhanterium sauveolens Desf. and Aristida pungens Desf. The most effective mode of resistance to sand mobility (accumulation and deflation) appears to be a change in the vegetative growth, i.e. the formation of adventitious roots in the accumulated sand and the development of aerial structures at a level corresponding with the new soil surface.

Pour evaluer les differents changements d'etat, ou les modifications de fonctionnement du milieu rural, induits par les perturbations naturelles, et surtout par les interventions de l'homme, l'observateur a le plus souvent recours a de simples caracteristiques du systeme ecologique etudie, mais aussi a l'utilisation d'indices complexes calcules a partir de parametres elementaires. Cet ensemble est designe sous le vocable general d'indicateurs d'etat et de fonctionnement du milieu. A titre d'exemple des indicateurs d'etat des systemes agro-ecologiques et du suivi du cycle culture-jachere en Afrique tropicale ont ete elabores. lls concernent les plantes indicatrices (par approche anthropique, ou demarche statistique), les indices de biodiversite, les indicateurs physiques et biochimiques des sols. L'utilisation de la meso et macrofaune du sol s'est revelee tres pertinente. Les indicateurs socio-economiques sont evoques. Certaines comparaisons sont faites entre la perception paysanne de l'etat du milieu et celle du chercheur. La mise au point et la determination des indicateurs n'ont pas toujours la reussite escomptee. ll faut distinguer, les indicateurs globaux voire regionaux qui dans l'ensemble sont les plus pertinents. A l'echelle des champs et parcelles du systeme, certains echecs sont dus a de mauvaises hypotheses, a une meconnaissance des cycles biologiques, a une forte heterogeneite du milieu et a une imparfaite connaissance de l'histoire agricole des parcelles. (Resume d'auteur)

The results of observations and measurements on five units of steppic vegetation in the mediterranean arid zone of S. Tunisia are presented in this paper. These units were totally protected against big herbivore grazing using barbed wire fencing during seven consecutive years.

Growth forms are considered from two viewpoints: a descriptive and a functional one. Mono-character growth forms and their biological spectra were used to test whether they can characterize certain underlying processes in Quercus ilex coppice in southern France. Correspondence analysis of 35 mono-character growth forms of 203 described taxa shows that location of renewal buds is a good integrating indicator of plant adaptations to the environment. Two of these characters (renewal bud location, i.e. Raunkiaer's main life forms, and leaf consistency) appear to vary significantly along a gradient of increasing environmental constraints, especially climatic ones.

Measurements carried out between 1971 and 1977 indicate the effect of rainfall on above-ground plant production. The site investigated consists of steppeland on sandy soil, dominated by the perennial dwarf shrub Rhantherium suaveolens with associated annual species. The average precipitation in this region (180 mm), produces about 1000 kg dry matter/ha. The ARFEJ model described, uses the most pertinent characteristics of the system so that production can be predicted under the assumption that water is the limiting factor. Seven model coefficients were calculated with the data of 1971–75. The results show (a) the considerable effect of rainfall distribution on evaporation from bare soil. The mean of this evaporation was 55 per cent (range 40–69 per cent) of total evapotranspiration; (b) during the short annual period of fast growth, the ratio of dry matter to water transpired would be about 1·26 g dry matter/kg H2O for annuals, and 1·39 g dry matter/kg H2O for perennial species. Over the whole year, the average efficiency of water use is 0·45 g dry matter/kg H2O for all species; (c) above 250 mm precipitation, the availability of nitrogen and/or phosphorus becomes the limiting factor for plant production and efficiency of water use decreases.

ResumeLes resultats presentes ici pour douze especes ne constituent qu'une fraction des observations faites dans le cadre d'un programme visant a la connaissance des cycles biologiques des especes des garrigues du Languedoc.Ces observations normalisees, s'integrent dans une etude de l'ensemble des zones a climat mediterraneen. La diversite phenomorphologique deja observee incite a poursuivre cette etude afin de tendre progressivement a l'etablissement d'une typologie phenomorphologique generale. Cela devrait permettre d'entreprendre alors des comparaisons du fonctionnement des ecosystemes mediterraneens entre la region mediterraneenne francaise et les autres regions du monde.

National audience; La fonction première de la jachère tropicale, est la reconstitution de certaines composantes de l'aptitude culturale du milieu ou "fertilité", avant culture suivante. Elle vient en complément ou substitution d'autres moyens, insuffisamment disponibles comme le fumier ou l'engrais. Cet article étudie les différents aspects de la restauration de certains états et fonctions de l'écosystème utiles, voire indispensables dans certains cas, aux cultures. Dans une première partie, la notion de fertilité est discutée, en particulier son caractère relatif à un contexte particulier, tant naturel (climat, sol, organismes de l'écosystème) que technique (moyens techniques, systèmes de culture, objectifs) et social (valeurs sociales, relations au foncier). Les indicateurs habituels de la fertilité sont discutés, en particulier la teneur en matière organique sous diverses formes. En s'appuyant sur de nombreux exemples ; l'article envisage dans une deuxième partie les processus généraux de transformation de la matière organique et des états du milieu pendant les deux phases du système culture-jachère : états initiaux critiques au moment de la mise en jachère, bilans organiques et minéraux liés aux groupes fonctionnels qui interviennent dans les processus de réhabilitation (micro-organismes, faune, graminées pérennes, ligneux). En troisième partie, les effets de différents systèmes culture-jachère sont analysés : culture itinérante à jachère longue, jachères naturelles exploitées courtes à graminées annuelles ou pérennes, jachères à graminées pérennes introduites ou plantées de ligneux. L'article se termine par des propositions générales pour la gestion de la fertilité. Trop souvent, les aménageurs n'ont pas suffisamment pris en compte les pratiques paysannes dans leurs diagnostics. Ces savoirs hérités d'expériences séculaires, et systèmes agro-écologiques constitués peu à peu, ont le mérite d'intégrer les contraintes du milieu naturel et social et les perturbations possibles. Les ignorer peut conduire à de graves échecs.