Dual cropping of rice (Oryza sativa) and green manure crops A cost effective management alternative for direct seeded semi-dry system of rice cultivation

Abstract

Field experiments were conducted at Agricultural Research Station, Mannuthy during 2004 and 2005 to fine tune the technology of dual culturing of rice ( Or yza sativa) and green manure crops to ensure the supply of re- quired quantity of organic manure to dry seeded rice in a cost effective manner. Two green manure crops viz., horse gram ( Macrotyloma uniflorum (Lam) Verdc) and cowpea [ Vigna unguiculata (L.) Walp.] sown along with rice were incorporated at 45 days after sowing by three methods viz., using cono weeder, spraying 2,4-D, and allowing self decomposition due to flooding at the onset of monsoon. Two levels of nitrogen (100 and 75% of recom- mended dose of N i.e. 90 kg) were super imposed over them. Dual cropping of cowpea with dry seeded rice could add about 12 t/ha of organic manure and resulted in a weed suppression of 69-75% and reduction in labour re- quirement for weeding (40 man-days/ha). This system guarantees 25% nitrogen saving (22.5 kg/ha) with 11% yield enhancement and increase in profitability (Rs 14,562/ha). The study revealed that, cowpea can be effectively incorporated by spraying 2, 4-D with effective weed control. The peak nitrogen release from concurrently grown cowpea coincides with the critical growth stages of rice, the panicle initiation stage, and thereby ensures availabil- ity of N at the critical stage.