Yield Response Factor of Sunflower under Deficit Irrigation at Different Growth Phases

Field experiments were conducted during two consecutive years (2014 and 2015) on Sunflower (variety: BARI Surjomukhi-2) crop at Bangladesh Agricultural Research Institute, Gazipur and Agricultural research station, Banerpota, Satkhira, to estimate yield response factor (ky) and drought sensitivity index (λi) at various phenological stages and ky for entire cropping period. There were nine irrigation treatments including full irrigation, 80% and 60% of root zone deficit at three growth stages (vegetative, pre-flowering and heading stage), 100%, 80% and 60% of root zone deficit at two growth stages except heading; and 100%, 80% and 60% of root zone deficit at two growth stages except pre-flowering. Results reveal that the values of ky and λi increased with the increase of intensity of water deficit at different growth stages. There were no statistical difference in paired ‘t’ test for individual growth stages and entire growth period. Overall, the ky values in Gazipur for 20% water deficit at three growth stages were 0.13, 0.09, and 0.11, while for 40% water deficit were 0.16, 0.12, and 0.15, respectively. For Satkhira, the ky values were 0.10, 0.06, and 0.09 for 20% water deficit at three growth stages, while 0.13, 0.08, and 0.12 for 40% water deficit. The ky value for 100% water deficit at pre-flowering and heading stage were 0.23 and 0.16 for Gazipur, while 0.16 and 0.13 for Satkhira, respectively. At 20% water deficit, sensitivity index (λi) at three growth stages were 0.058, 0.021, and 0.048 for Gazipur, while 0.046, 0.019 and 0.036 for Satkhira, respectively. For 40% water deficit, λi values were 0.063, 0.029, and 0.053 at Gazipur, while, 0.06, 0.024 and 0.045 at Satkhira, respectively. The λi values for 100% water deficit at pre-flowering and heading stage were 0.12 and 0.10 for Gazipur and 0.069 and 0.06 for Satkhira. The highest ky values for entire growing period (irrigating 60% root zone deficit at vegetative and heading stage) was 0.54 and 0.64, followed by 80% and 100% of root zone deficit at vegetative and heading stageat Gazipur and Satkhira, respectively. This value was very close to 80% and 100% of the root zone deficit in terms of entire growing period ky value. Therefore, pre-flowering stage was the critical stage and irrigation should not be applied at 100%, 80% and 60% of the root zone deficit at vegetative and heading stage, rather it should be applied at 80% and 60% of the root zone deficit at vegetative and pre-flowering stage, respectively, for water limiting areas.