Kazi Tani, Choukry2014-07-162014-07-162014-07-16https://dspace.univ-tlemcen.dz/handle/112/5698The present thesis deals with the botany, agronomy and phyto-ecology of weed communities occurring in irrigated or dry (rain) crops as well as fallows of the oranian phytogeographic territory (North-West Algeria). The first part of this study is grounded on 547 surveys fields in the three phytogeographic subdivisions, and from sea level to 1 200 m, to describe general characteristics of the weed flora as well as botanical, phytogeographical and biological traits of the 425 recorded species. The second part is interested in frequency analysis and mean overlapping of every weed species. The projection of the species on a diagram where are casted relative frequencies on abscissa and mean abundances on ordinate allowed to distinguish 6 species groups according to their infestation rate, then their agronomic importance. Two species, Convolvulus arvensis L. and Sinapis alba L., where qualified as "general major" weeds. The third part treat the whole phyto-ecological data using non symetric correspondance analysis under environmental compulsion which indicated that the principal source of species variation in the fields of Oranie are the crop systems. Surveys from cereal plots have been the subject of a partial analysis throughout the BIOMECO software. The factorial correspondance analysis diagram of the species- surveys-factors matrix reveals five ecological groups which have been discussed on the basis of edaphic and climatic criteria. Keywords : Weed flora – Agrosystems – Phyto-ecology - Negative effects - Non symetric correspondance analysis - Factorial correspondance analysisfrphytogéographique, Weed flora, Agrosystems, Phyto-ecology, Negative effects, Non symetric correspondance analysis , Factorial correspondance, analysisThesis