COMPETITION OF FOUR ETHIOPIAN BREAD WHEAT CULTIVARS WITH VARYING DENSITIES OF WILD OAT

摘要

Competitive interactions of four spring bread wheat cultivars (Triticum aestivum L.) with four wild oat (Avena fatua L.) seedling densities were assessed in field studies in southeastern Ethiopia during three cropping seasons (1991-93). Grain yield reduction of wheat was linearly proportional to the seedling density of wild oats, but yield reductions at the maximum density of 90 weed seedlings m~(-2) ranged from 26 to 63% across the wheat cultivars. The semidwarf cultivar Dashen was the most sensitive to wild oat competition, while the intermediate height cultivar Enkoy was the least affected. Wheat cultivars varied markedly in their ability to suppress A. fatua tillering and seed production, differentially affecting wild oat seed and straw yield, panicle production, seed number panicle, and thousand kernel weight. Percent N in wheat grain and straw increased linearly in response to wild oat competition, while %N in wild oat seed varied inversely with wild oat seed yield (i.e., in response to the competitiveness of wheat cultivars). Percent P did not vary in wild oat straw or grain; for wheat, only straw P content varied among wheat cultivars. Total N uptake by the mixed canopy of wheat and wild oat varied among the wheat cultivars and increased linearly in response to wild oat density, while total P uptake only varied among wheat cultivars. The mean proportion of total N, total P and total biomass contained in the wild oat fraction was 30.5, 31.9 and 25.1%, respectively, indicating that wild oatwas more successful than wheat at utilizing available soil N and P. Wheat N use efficiency (NUE) varied among cultivars and decreased with wild oat density while wild oat NUE only varied among wheat cultivars. Wheat and wild oat P use efficiency (PUE) did not vary across either main factor. Given the limited access of Ethiopian peasant farmers to grass killing herbicides, wheat breeders should be encouraged to exploit such variability, and develop germplasm with a greater inherent ability to compete with wild oats.