Drought Resistance of NERICA Compared with Asian Rice, African Rice and Millets in the Field with Different Fertilization Levels

Recently NERICA (New Rice for Africa) was developed by a crossing between African rice (Oryza glaberrima Steud.) with Asian rice (Oryza sativa L.) in West Africa, and is considered to be drought resistant, but it is not clarified enough about the difference in reactions under dry condition. In this research, NERICA, Asian rice, African rice and millets were cultivated in the field under drought condition with different fertilization levels to compare dry matter production, stomatal and leaf characteristics and water absorbing characteristics to comfirm the characteristics of NERICA under drought condition. Fertilization levels were 6 gN/m2 in standard fertilization level and 2 gN/m2 in low fertilization level. Stomatal conductance was measured by porometer and soil water contents at individual depths (0-60 cm) were measured by TDR method. Leaf thickness was measured by micrometer and SPAD value was determined with SPAD meter. In standard fertilization level under drought condition, top dry weight at harvest was high in Dular, drought resistant Asian rice cultivar. Dry weight at harvest in low fertilization level tended to be higher than that grown in standard fertilization level. In low fertilization level one of NERICA showed high dry weight. Dry weight of glaberrima parent of NERICA was high in both standard and low fertilization levels, but proportion of dead leaf was high. In standard fertilization level, Dular showed highest stomatal conductance followed by sativa parent of NERICA and one of NERICA. In low fertilization level sativa parent of NERICA, Dular and one of NERICA showed high stomatal conductance and it tended to be higher than in standard fertilization level. Glaberrima parent of NERICA showed low stomatal conductance in both fertilization levels. Average soil water content at 0-60 cm depth before harvest in standard fertilization level was low in Dular followed by glaberrima parent of NERICA. In low fertilization level soil water content was maintained highest in one of NERICA. Soil water content at 0-20 cm depth in standard fertilization level was low in glaberrima parent of NERICA. There was large cultivar differences in soil water content at 40-60 cm depth and soil water decreased significantly in Dular in standard fertilization level. On the contrary it was maintained highest in one of NERICA in low fertilization level. Dry weight was high in Dular, but soil water content decreased especially in the standard fertilization level. On the contrary, dry weight was high in one of NERICA and soil water content was maintained high especially in low fertilization level and at deep soil layer (40-60 cm depth). There was a significant correlation (r=0.907**) between average stomatal conductance and dry weight at harvest except glaberrima parent of NERICA. In low fertilization level stomatal conductance and dry weight at harvest tended to be larger than in standard fertilization level. There was a significant correlation (r=0.892**) between average leaf thickness and dry weight at harvest except glaberrima parent of NERICA and cultivar with thick leaf tended to maintain high dry matter production. There was a significant correlation (r=0.828*) between average leaf thickness and SPAD value in rice. In one of NERICA leaf thickness and SPAD value were higher in low fertilization level than in standard fertilization level. SPAD value tended to be low in Dular. High leaf thickness and SPAD values seem to be effective to maintain dry matter production under limited water condition with high water use efficiency. NERICA seems to be appropriate for the cultivation under drought condition with the effective use of limited water for the sustainable crop production especially in low fertilization level.