Impact of weeding methods on the floristic diversity and valorization of weeds in citrus orchards in the region of Tlemcen (Northwest of Algeria)

Abstract

The present thesis deals with the impact of mechanical and chemical weeding on the composition of weed flora in citrus orchards as well as the valorization of 20 % of this flora. The first part of this study was grounded on 168 surveys before and after each weeding (mechanical and chemical) in comparison to a control without weeding. A total of 88 species, belonging to 71 genera and 30 botanical families were identified. The Mediterranean elements (64%), therophytes (51%) and dicotyledons (64%) were dominant. the ANOVA revealed the existence of a significant spatial-temporal difference in the mean species richness between the stations (control vs. chemical and mechanical). In addition, the species richness before weeding tended to be higher than that after it. The second part was interested in the evaluation of the antioxidant activities (DPPH, ABTS and chelating power) and the phenols and flavonoids content of 19 weed species (representing 20 % of the total flora) that aimed at valorizing citrus weeds. Four species (I. viscosa L., S. montanaL., R. peregrina L. and R. tingitana L.) were characterized by their richness in phenols and flavonoids and as good DPPH scavengers. Principal component analysis permitted to find two main groups: that in which I. viscosa L., R. tingitana L. and S. montana L. possessed relative high amounts of total phenols and good capacity for scavenging ABTS free radicals, whereas M. sylvestris L., E. spinosa (L.) Campd., H. helix L. and R. peregrina L. were good scavengers of DPPH free radicals and chelators of ferrous ions. This can be the first step for possible mixtures of these extracts in order to evaluate the possible synergistic effect among them, acting simultaneously as free radical scavengers and chelating agents. The third part treated the evaluation of the nutritive value and the mineral composition of 19 weeds which aimed to valorize these species to be used as fodder for animal nutrition. The results showed that O. pes-caprae was the species exhibiting the best NDF-Digestibility. As for the mineral composition, Ch. coronarium showed the highest K and Ca levels while E. spinosa presented the higher Mg and Zn concentrations. For Fe, Ch. segetum was the richest species. Also, I. viscosa had the best Mn content and H. helix recorded the higher P level. These results suppose the potential use of weeds in pharmaceutical, industrial, and cosmetic industries but also for animal feeding.