Vitesse d'emission des feuilles des brins maitres d'une orge de printemps cultivee a plusieurs altitudes : differences liees au type de tallage et aux milieux

French. Cette étude compare des cultures d’un même lot de semences mises en place à 320 m, 880 m et 1 120 m d’altitude en sortie d’hiver, et après le réchauffement printanier à 880 m. Des échantillons des peuplements obtenus sont prélevés après le début de montaison, vers l’arrêt du tallage. Les plantes sans talle, parfois très fréquentes en montagne, émettent leurs feuilles plus lentement que celles qui tallent à partir du noeud de 1er feuille (type T1+). Pour un même type de tallage et dans une situation culturale donnée, l’émission est plus rapide en peuplements clairs bien alimentés en azote. Les plantes de type T1+ ayant poussé en peuplements clairs bien alimentés en azote présentant des phyllochrones différents entre situations culturales, en fonction des conditions climatiques initiales. Les facteurs autres que climatiques pourraient aussi agir par conditionnement initial des plantules.

English. Our experimental design compared several crops sown in the highlands of the French Massif Central to a control sown at a low elevation, all of them using the same seed lot (cultivar and origin). The crops were sown in late winter at each elevation (320, 880, 1 120 m) and again somewhat later at 880 m. Plant emergence was relatively homogeneous (table I). Sample plants were harvested for investigation following the onset of shooting (table II). They were subjected to well differentiated climatic conditions (fig 1, table VI), and their mineral levels already reflected the experimental conditions (table III). Plants without tillers (type "ST") were numerous at times in the high elevation stands (fig 2). They put forth leaves at a slower rate than plants showing the usual type of tillering from the first leave node onwards (type T1+; fig 2; table V). In a given growing location plants belonging to the same tillering type put forth leaves more rapidly in thin stands that were well supplied with nitrogen (table VI). The phyllochron of type T1+ plants was variable among similar thin stands well supplied with nitrogen but grown at different locations (table VII). These phyllocrons could be associated with the climatic criteria reported in the literature (table VIII), according to the means by which time is measured (fig 3). The late of foliar emergence was modified according to tillering type, mineral nutrition, stand density, and climate. All these fators seem to act through an initial conditioning of the seedlings.