Effects of the reduction of drought stress using supplementary Irrigation for Sunflower (Helianthus annuus) in dry farming conditions

It is possible to omit or decrease drought stress in crops, which have been cultivated in dry farming conditions. Stress is a result of unusual and physiological process that is induced by the effect and combination of one or more biological and environmental factors. Sunflower (Helianthus annuus) isa crop compatible to wet moderate regions. It is also cultivated in semidry regions using irrigation and without irrigation too. In order to cultivate this plant in such a region, it is necessary to use appropriate agrotechnical methods in addition to drought tolerant cultivars. Obviously, by omitting or decreasing the stress using a supplemental irrigation, production output of this plant could be increased. To confirm the effects of appropriate supplemental irrigation, three cultivars of sunflower were studied under three levels of water stress conditions using 9 treatments in 3 replications, in a 3x3 factoriel experimental design. Plants were supplementary irrigated in flowering and seeding set stages. In order to increase the accuracy of evaluation, a treatment with no irrigation was also used as control. The traits such as total biomass, seed yield, and oil percentage, were studied. Results from this experiment showed that irrigation in flowering stage increases the yield of seeds more than 60% and the percentage of oil about 25% comparison to the control. Total biomass was also increased due to the irrigation in different growth stages. Oil percentage was increased from 33% in the state of drought stress to a maximum of 41% after using a supplementary irrigation in flowering time. None of the cultivars were recommended for the region, since there was no significant difference between three cultivars.