Field experiments were conducted to find out the effectiveness of dual cropping of green manure crops, its methods of incorporation and levels of nitrogen on weed management and to study the cost effectiveness of the system of dual cropping of green manure crop in semi-dry rice. Among the two green manure crops, cowpea (Vigna unguiculata (L.) Walp.) was more effective in suppressing weeds and recorded the minimum weed population and weed dry matter compared to horse gram (Macrotyloma uniflorum (Lam) Verdc). Incorporation of green manure crops with 2,4-D significantly reduced weed population and weed dry weight compared to other incorporation methods. Nitrogen application at different levels had no significant influence on weeds. Dual cropping of cowpea and its incorporation at 45 days after sowing using 2,4-D was able to meet 25% N requirement beside reducing the weeds in semi-dry rice with increased productivity and profitability