Journal of Experimental Agriculture International

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 (k_y) and drought sensitivity index (λ_i) at various phenological stages and k_y 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 k_y and λ_i 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 k_y 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 k_y 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 k_y 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 (λ_i) 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, λ_i values were 0.063, 0.029, and 0.053 at Gazipur, while, 0.06, 0.024 and 0.045 at Satkhira, respectively. The λ_i 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 k_y 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 k_y 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.