A field experiment was carried out at Rajendra Agricultural University, Pusa, Samastipur, Bihar during kharif seasons from 2004 to 2006 to assess the weed utility as a bio-nutrient source in rice cultivation. The results revealed that among organic sources, the use of water hyacinth (2.5 t/ha) FYM (5 t/ha) recorded the maximum growth, yield attributes and grain and straw yields of rice which was closely followed by water hyacinth (2.5 t/ha) + vermicompost (1 t/ha), Parthenium (2.5 t/ha) + vermicompost (1 t/ha), Parthenium (2.5 t/ha) + FYM (5 t/ha) and water hyacinth (2.5 t/ha) + poultry manure (1 t/ha). The maximum net return (Rs 11148/ha) and benefit: cost ratio (1.61:1) were also recorded by water hyacinth (2.5 t/ha) + FYM (5 t/ha). The highest available N (185.67 kg/ha), available P (26.38 kg/ha) and exchangeable K (525.6 kg/ha) were recorded by water hyacinth (2.5 t/ha) + FYM (5 t/ha). Water hyacinth or Parthenium either alone or in combination with other organic sources had a better utility as a bio-nutrient source. Among the inorganic levels, application of 100%, recommonded dose of fertilizer (RDF) produced significantly higher grain and straw yields as compared to other nutrient levels. Application of full dose of recommended NPK recorded significantly higher net return (Rs 10974 /ha) over 50% RDF which was closely followed by 75% RDF. Full dose of recommended NPK application had significant and beneficial effect on rice grain yield and improved the soil NPK status. The interaction effects between organic sources and inorganic levels were found to be non-significant