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SUMMARYWheat was planted at different altitudes in the Ethiopian highlands. Increased altitude led to a lower neutral detergent fibre (NDF) content and a higher in vitro organic matter digestibility (IVOMD) of the leaf blades, leaf sheaths and stems. The varieties tested did not differ in NDF content, however, because of the improved NDF digestibility of all three straw fractions. The semi-dwarf varieties had a higher IVOMD than the standard tall wheats. The local durum wheat variety showed a much higher sodium content and a more favourable Na:K ratio. Undersowing with an equal mixture of Trifolium ruepellianum (Fres.) and Trifolium steudneri (Schwf.) led to a small reduction in straw yield but increased the crude protein content of the crop residues from 2.3 to 7.1% and the IVOMD from 44 to 51% as compared to the sole wheat stand.

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Germination and survival of indigenous annual Trifolium species were studied. Seedlings naturally emerging in the field and from sown seeds in pots were regularly counted and uprooted, and survival was studied by monitoring colour-coded seedlings. Differences in recruitment of Trifolium species were strongly related to the rainfall pattern. In the fallow (crop) lands, no seedling survived the dry season between the short and main rainy periods during the year, while in the natural pasture, 8% of the seedlings survived into the main growing (rainy) season. Occasional rains occurring in the dry period (between the two rainy periods) also induced successions of germination and seedlings death, and therefore depleted the soft seed reserve in the soil by the beginning of the main growing season. As temperature fluctuations were minimal during the main rainy season, the rate of seed softening was low, affecting new germinations. This had a significant impact on the quality of the natural pastures on which livestock in the highlands are dependent. RésuméOn a étudié la germination et la survie de l'espèce annuelle indigène de Trifolium. Les plants qui croissent naturellement et ceux qui proviennent de semences semées dans des pots ont été régulièrement comptés et déracinés, et on a étudié la survie en surveillant les plants selon un code de couleur. Les différences constatées dans les repousses de l'espèce Trifolium étaient fortement liées au schéma des chutes de pluies. Dans les terres cultivables laissées en jachère, aucun plant ne survivait à la saison sèche entre la petite et la grande pérode des pluies pendant l'année, tandis que dans les pâturages naturels, 8% des plants survivaient jusqu'à la principale saison de croissance (pendant les pluies). Des pluies occasionnelles survenant pendant la période sèche (entre les deux périodes de pluies) provoquaient aussi la germination puis la mort de pousses et diminuaient ainsi la réserve de semences tendres présentes dans le sol au début de la période de croissance principale. Comme les fluctuations de température étaient minimales pendant la principale période de pluies, le taux d'attendrissement des semences était faible, affectant les nouvelles germinations. Ceci avait un impact significatif sur la qualité des pâturages naturels dont dépend le bétail des hauts plateaux.