Performance and adaptation of rice genotypes under continuous flooding and alternate wetting and drying irrigation scheme

The field experiment was laid out in split plot with four replications where irrigation treatments were used as main plots and the genotypes as the subplot to study the effect of alternate wetting and drying on the morphological and physiological traits of rice genotypes and subsequently on their grain yield and water productivity. Five rice genotypes, namely IR64 (improved line variety or I2, IR74-286-55-2-3-2-3 (line genotype I16) and IR77-266 H (hybrid or H10) were used. This experiment was conducted at the International Rice Research Institute (IRRI) [Los Baños, Laguna, Philippines] during the 2005 dry season. Alternate wetting and drying irrigation scheme influenced some morphological and physiological traits of the different rice genotypes. Hybrid genotype H10 had higher number of productive tillers, harvest index, specific stem length, lower specific leaf area, higher growth rate, lower shoot root ratio, increasing root weight, grain yield and higher water productivity. Genotypes had different response to changing soil moisture. Hybrid genotype H10 had the lowest water consumption. High water consuming genotypes I15 and I16 had higher leaf are (hence higher stomates), which led to greater evapotranspiration (ET), but these were also the highest yielding genotypes. Crop maturity duration increased the crop water demand. The computed irrigation water usage was about 69.8 cu m/day/ha. The 12-16 days longer field duration of 115 and 116 translated to about 837-116.8 cu m/day/ha additional irrigation water. This led to the lower water productivity of these genotypes. Alternative wetting and drying irrigation scheme (AWD20) consumed significantly the highest amount of water compared to CF and AWD40. Though statistically significant, water productivity was lowest under AWD20 at 1.0 g/li whereas it was 1.14 and 1.12 g/l in CF and AWD40, respectively. Grain yields were not significantly different in the three irrigation schemes at 9.45, 8.32 and 8.30 t/ha for CF, AWD20 and AWD40, respectively.