L. PuelschenUniversity of Hohenheim Institute for Plant Production in the Tropics and Subtropics
PO Box 700562, D-700 Stuttgart, FR Germany
A survey of the agrestal weeds in 179 vertic soils was conducted during the 1983/1984 and 1985/1986 cropping seasons within Shewa Province, Ethiopia, to relate species and cover to topographic, edaphic and agronomic factors. Topographic and agronomic data were gathered at randomly selected sites. Weed cover was estimated using the Braun-Blanquet method.
Surface soil samples were collected at 165 sites. The mean soil reaction was slightly acidic (pH 6.7) and became more acidic with increasing elevation. Clay contents varied considerably (25-80%) and 75% of all samples were classified as clay soils. High mean CEC (44 meq/100 g soil) was tentatively attributed to the prevalence of montmorillonite clay minerals. The majority of the samples tested had ample K based on critical levels of K-saturation and were not deficient in Mn, Fe and Cu. whereas 22% were deficient in Zn.
The diversity of the weed flora (332 species)' including broadleaved (253) and leguminous (55) species and a high number of perennials (32% of all species with a frequency of occurrence of >20%) was attributed to the topographic and edaphic complex and the low-input farming system.
Weed cover decreased with a decline in elevation. It was found that weeds could be classified according to their distribution within three elevation zones. The most common species throughout the surveyed area were Digitaria scalarum (Schweinf.) Chiov, Cynodon dactylon (L.) Pers., Cyperus rotundus L., Guizotia scabra Meisn. and Galinsoga parviflora Cav.
