Effect of Deficit Irrigation and Plant Density on Growth and Seed Yield and Some Morphological Traits of Autumn Safflower)Carthamus tinctorius L(

IntroductionVegetable oils such as safflower oil, due to high amounts of unsaturated fatty acids, play an important role in the fat balance of human diet and can reduce blood cholesterol level. Drought as the most important factor controlling the performance of the products, on a variety of factors that affect plant growth and yield (Ghamarnia and Sepehri, 2010). Although safflower is a drought resistant plant, but drought has significant effects on its duration of phenological stages, thus cause a significant reduction in yield, yield components, growth and some morphological traits such as plant height and distance to the first bifurcation branches from soil surface (Khoshnam et al. 2012). When the distance between plants in the row is low, vacancies are not green. Low density, especially in row plant spacing is not desirable. This experiment aims at identifying the critical stages of water and specifies the appropriate number of plants in conditions of stress and lack of tension in the area as well.
Material and MethodsIn order to evaluate the effect of deficit irrigation and density on growth, seed yield and some morphological traits of a local variety of autumn safflower, an experiment was conducted with a spilt plot arrangement based on randomized complete block design with four replications at Research farm of Faculty of Agriculture, Birjand University in 2013-2014. Irrigation levels (complete irrigation, irrigation until flowering and irrigation until heading-bud stage) and plant density (20, 30, 40 and 50 plant per square meter) allocated randomly in main plots and subplots, respectively. Phonological aspects (number of days to emergence, stemming, heading bud, 50% flowering and physiological maturity) were recorded. The terms consisted of plant height, distance to the first bifurcation branches from soil surface and number of primary and secondary branches and seed yield. SAS ver. 9.1 statistical software was performed to measure the results of the analysis of variance (ANOVA) and means were compared with LSD test in 5% probability level.
Results DiscussionResults showed a significant reduction in plant growth period, plant height, distance to the first bifurcation branches from soil surface and number of primary and secondary branches in the irrigation until heading-bud treatment. The yield loss in this treatment was caused by early flowering and decrease in flowering period, seed filling period, maturity stage and yield components. It seems that the heading-bud stage is the most critical stage of the crop growing under water deficit conditions. Since all of the measured parameters had a positive correlation with seed yield, so a reduction of seed yield under the "irrigation until heading-bud treatment" is obvious. By increasing the plant density, plant height and distance to the first bifurcation branches from soil surface was increased but number of days until maturity and number of primary and secondary branches was reduced. In addition, the highest seed yield was obtained from full irrigation treatment with density of 40 plants in m2. In all plant densities, lowest seed yield was observed in the "irrigation until heading-bud" treatment. As it seems that this growth stage is the most susceptible stage of the crop to limited water, optimum irrigation in this stage may case a significant increase in seed yield.
ConclusionAccording to the results of this experiment in order to achieve the maximum yield of safflower in Birjand region, full irrigation and density of 40 plant.m-2 is suggested. Supplementary irrigation during heading-bud stage is necessary to prevent a sharp drop in seed yield. The density of 40 plant.m-2 of safflower can cover the canopy faster and due to a reduction in soil evaporation, it can postpone the drought stress to the end of the growing season. This density, also with increasing the growing season, increasing the plant height and decreasing the number of low or non-fertile branches, results in better plant growth and thus helps to produce more seeds.