<i>In situ</i> green manuring with daincha (<i>Sesbania aculeata </i>Pers.): a cost effective management alternative for wet seeded rice (<i>Oryza sativa </i>L.)

Abstract

Two field experiments were conducted on simultaneous growing and incorporation of daincha (Sesbania aculeata Pers.) in wet seeded rice in the humid tropics of Kerala, India. The objectives were to optimize the stage and method of incorporation of daincha, to evaluate N release pattern following green manure addition, and to assess its potential to supplement the nutrient requirement of rice crop, besides evaluating the cost effectiveness of in situ green manuring. Treatments consisted of two stages of incorporation of in situ grown daincha (20 and 30 days after sowing), three methods of incorporation (using cono weeder, spraying 2, 4-D at1.0 kg•ha–1, and spraying met sulfuron methyl at 5.0 g•ha–1), and two levels of N application (100 and 75% of the recommended N dose of 90 kg•ha–1). Wet sown rice without daincha, receiving 5 Mg•ha–1 farm yard manure and 90, 45, 45 kg N, P, and K ha–1 respectively, served as control. The experiment was laid out in a completely randomized factorial design during 2004 and 2005 and was replicated thrice. Incorporation of daincha at 30 days added about 14 Mg•ha–1 of organic matter, reduced weed population by 70% and supplemented about 25% of the N requirement of rice. Peak release of NH4 - N from daincha coincided with panicle initiation stage of rice, signifying N availability at the most critical physiological stage (synchrony in the release of green manure held nutrients and nutrient uptake by the rice crop). Green manuring with intercropped daincha also enhanced rice yield by 544 kg•ha–1 and returns by Rs.10220 ha–1, implying the potential of integrated nutrient management systems to augment crop productivity and profitability.