Effects of fertilization regime and herbicide treatment on segetal flora abundance, composition and functional diversity in common buckwheat (Fagopyrum esculentum Moench) agrocenosis

Weed management must reduce crop interference while avoiding unnecessary simplification of arable plant assemblages. We assessed how buckwheat cultivar, nitrogen-fertilization regime and pre-emergence herbicide treatment affected weed abundance, biomass, species richness, taxonomic diversity, assemblage composition and functional diversity during a three-year field experiment. The fertilization regimes supplied the same total nitrogen rate but replaced ammonium nitrate progressively with calcium cyanamide, a nitrogen fertilizer with transient phytotoxic activity that may provide a non-herbicide component of weed regulation. Relative to fertilization solely with ammonium nitrate, fertilization solely with calcium cyanamide reduced dicotyledonous weed abundance by 39.0%, species richness by 13.0% and weed dry biomass by 20.0%. The metazachlor + clomazone treatment reduced monocotyledonous weed abundance by 83.0%, dicotyledonous weed abundance by 40.5% and weed dry biomass by 36.4% relative to untreated plots. Herbicide treatment also altered community composition, largely through the reduced abundance of Echinochloa crus-galli and Chenopodium album and the greater relative contribution of Persicaria maculosa and Thlaspi arvense . Metazachlor + clomazone increased functional evenness relative to the untreated plots and altered functional divergence and dispersion relative to linuron. These patterns indicate herbicide induced shifts in weed community structure. Metazachlor plus clomazone suppressed several dominant weed species while allowing a greater relative contribution of less abundant species with different functional characteristics, indicating herbicide-induced shifts in weed assemblage structure.