The field experiments to study the ‘floristic dynamics’ of weeds as influenced by sowing time and system of cultivation of rice genotypes’ were carried out in coastal Odisha during 2009 and 2010 in split split-plot design with early (20 June), normal (5 July) and late (20 July) sowings in main plots; best management practice (BMP), system of rice intensification (SRI) and modified SRI (MSRI) in sub-plots and; hybrid Ajay and cv. Tapaswini in sub sub-plots, giving rise to 18 treatment combinations that were replicated thrice. Early sowing of rice was the most promising in recording significantly the highest grain yield that provided an additional yield 6.08 per cent over normal date of sowing. While normal sowing produced significantly higher grain yield (13.77 per cent) over delayed sowing due to diminishing trend in yield components of late sown rice. SRI produced 10.17 per cent less yield f than that of MSRI but 21.69 per cent more than in BMP. Hybrid Ajay produced 9.07 per cent more grains than cv.Tapaswini which could possibly be due to genetic potential of the former accompanied with lesser weed infestation. Weed biomass at 40 DAS decreased significantly with delay in sowing beyond 20 June. SRI had the highest weed biomass followed by MSRI and BMP. BMP had the highest per cent of sedges while MSRI and SRI had the highest per cent of grasses and broad leaved weeds, respectively.