Influence of weeding regimes on composition and diversity of weed species in upland rice (oryza sativa l.) field

Abstract

Abundance of weed species promotes biodiversity within agroecosystems whereas it constitutes biotic stress in arable farmland. There is insufficient information on effects of weed species composition and diversity’ on performance of upland rice in Nigeria. Therefore, a 2-year field study was conducted to assess the weed species composition, diversity and its effects on growth and yield of upland rice cultivars. A split-plot design was used with two rice cultivars (CGI4 and NERICA2) as the main plot treatment and four weeding regimes as the sub-plot. Weeds were sampled from each plot with a 0.5 m * 0.5 m wooden quadrat. The weed species were identified to species level, counted and recorded. Data collected were used to calculate relative frequency, relative density and relative importance value for each species. Dominance, Simpson, Shannon Wiener and evenness indices were used to describe the community structure. The flora of the study site varied widely in occurrence. Twenty four weed species comprising 16 annual herbs, four sedges, three grasses and one commelinaceae Family were found interfering with upland rice. The field had highly diversed annual, herbacious, dicotyledonous and monoc.tyledonous weed species native to tropical ecosystems. The upland rice field had evenly distributed rich and highly diversed weed community. Cultivar CGI4 performed significantly better than NERICA2 with respect to number of leaves (32.56) formed, tillering (8.67) and panicles (8.25) produced. The CG14 plot left unweeded throughout the study period had significantly highest weed biomass (6.16 t/ha) compared to NERICA2 plots. Absolute weed interefence reduced grain yield in NERICA2 and CGI4 cultivars by 42.7 % and 30.9 %, respectively. The biomass accumulated by weed species were inversely related to grain yield (t/ha) in both seasons.