Weed flora in the reclaimed lands along the northern sector of the Nile Valley in Egypt

Deserts comprise about 95% of the total land surface of Egypt; therefore, their potential for production must be assessed. Weed communities are mainly affected by the environment, and studies may increase our knowledge of the relationship among the weed flora, soil properties, crop rotation, soil management, fertiliser usage, and weed control. The area under study is one of the most recently reclaimed lands. The recorded 150 species in the monitored 19 sites were distributed within 33 families. The species-rich families were: Poaceae (31), Asteraceae (23), Brassicaceae (13), Chenopodiaceae (12), and Fabaceae (12). Chorological analysis revealed that the widely distributed species belonging to cosmopolitan, palaeotropical, and pantropical chorotypes constituted about 39.3% of the recorded flora. Pure Mediterranean species were very poorly represented, while biregional and triregional Mediterranean chorotypes constituted 28%. Saharo-Arabian chorotypes, either pure or penetrated into other regions, constituted 32%. Ubiquitous species with wide amplitude were Cynodon dactylon (L.) Pers. and Sonchus oleraceus L. Species richness varied from one crop to another. The winter weeds represented the main bulk of the recorded species within each crop, desert perennials exhibited notable variations, and margin species were the lowest. Redundancy analysis demonstrated the effect of soil organic matter, coarse sand, fine sand, silt, and soil saturation point on the spatial distribution of weed communities. The species-environment correlations were higher for the 4 axes, explaining 64.1% of the cumulative variance. The variations in soil pH, bicarbonates, ammonia, silt, and sulphate contents classified the vegetation into 4 site (vegetation) groups. Application of cluster analysis of species in crop-orchard farmlands resulted in 4 floristic groups (A-D). The weed species of the 2 winter crops, Egyptian clover and wheat, separated in Group A, tomato (winter/summer crop) in Group B, maize as a summer crop in Group C, and weeds of olive orchards and vineyards in Group D. This demonstrated high significant correlations between the olive and vineyard orchards (P < 0.01), and between the 2 winter crops, wheat and clover.