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

Field experiments were conducted at Agricultural Research Station, Mannuthy during 2004 and 2005 to fine tune the technology of dual culturing of rice (Oryza sativa) and green manure crops to ensure the supply of required 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 recommended 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 requirement 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 availability of N at the critical stage.