Direct and residual effect of concurrent growing of dhaincha (Sesbania aculeata) in wet-seeded rice (Oryza sativa) on the productivity of rice–rice cropping system

unknown. Field experiments were conducted during rainy (kharif) and winter (rabi) seasons of 2004–05 and 2005–06 at Agricultural Research Station, Mannuthy, Thrissur, to find out the effective methods and optimum stage of incorporation of dhaincha (Sesbania aculeate Pers.), to work out the nutrient saving to the current and residual crop and to study the cost effectiveness of the system of concurrent growing of dhaincha in wet-seeded rice (Oryza sativa L.). Concurrently grown dhaincha was incorporated at 2 stages, i e 20 and 30 days after sowing (DAS) by using one of the 3 methods, viz using cono weeder, desiccating dhaincha by spraying 2, 4-D @1.0 kg/ha or by spraying met sulfuron methyl @ 5.0 g/ ha and supplied with 2 levels of nitrogen (100 and 75% of the recommended dose). A second crop of transplanted rice was raised in the same plots after dividing the plots equally into 2 sub-plots. Two levels of nitrogen (100 and 75% N) were super imposed over them. Incorporation of concurrently grown dhaincha at the age of 30 days resulted in a yield enhancement to the tune of 0.84 tonnes/ha, increase in profitability (Rs 12 520/ha) with assured addition of 14 tonnes/ ha of organic manures and 70% weed suppression. In terms of weed management and in places where it is difficult to use cono weeder, dhaincha can be effectively incorporated by spraying 2, 4 –D or metsulfuron methyl without affecting the yield. By growing of dhaincha along with rice and its subsequent incorporation helped to reduce the use of nitrogen fertilizer to the current crop by 25% without affecting the yield. To realize the highest yield (3.88tonnes/ha) from succeeding transplanted rice, 100% of the recommended N should be supplied to the succeeding rice (Oryza sativa L.) in the rice–rice system.