RICE AND WHEAT YIELDS IN RELATION TO BIOMASS OF GREEN MANURE LEGUMES

This study was conducted to assess the relationship of green manure (GM) legumes grown in the gap between wheat (Triticum aestivum) harvest and rice (Oryza sativa) planting for sustainable rice-wheat system. Six GM legumes viz. mungbean (Vigna radiata), cowpea (Vigna unguiculata), soybean (Glycine max), sesbania (Sesbania rostrata), pigeonpea (Cajanus cajan) and guar (Cyamopsis tetragonoloba) were tested for the same in rice-wheat cropping for three consecutive years (2001-04) at Agriculture Research Institute, Tarnab, Peshawar (Pakistan). The average of three years data showed that the greatest DM shoot biomass of 2366 kg ha-1 was obtained for sesbania and the lowest of 992 kg ha^-1 was obtained for guar. The legumes biomass of only 2002 and 2003 were analyzed for different nutrients (N, P, K, Zn, Cu, Fe, Mn) and, on average, the greatest amount of nutrients were found in cowpea (86.69 kg ha^-1) and the lowest in soybean (37.12 kg ha^-1). The regressions equations developed from the data showed that the yields of both rice and wheat had strong relationship both with the shoot biomass and amount of nutrients in shoot biomass of GM legumes. These results suggested that grain and straw yields of both rice and wheat crops have shown strong relationship with the total biomass of GM legumes. The improvement gained in crop yields from GM legumes could be attributed to improvement in the soil conditions and nutrient status of the soil. It is therefore recommended that green manure legumes should be encouraged for sustainable soil and crop productivity in rice-wheat system.