Usage possibilities of plant based measurement techniques in irrigation scheduling of sunflower

In this study, effects of different amount of irrigation applications on water use, yield and yield parameters of sunflower plant in Tekirdağ conditions and usability of plant-based measurement techniques in irrigation applications were investigated. The six different irrigation water amounts with 7 days interval applied based on a ratio of Class A pan evaporation as 0, 25, 50, 75, 100 and 125% were created in the research. Leaf area index, leaf water potential, chlorophyll content, stomal resistance, photosynthesis rate and transpiration rate were measured as plant-based measurement techniques. In the first year of the study, irrigation water was applied to all experimental subjects between 67,0 and 334,8 mm with 7 irrigation applications and 133,7 to 668,1 mm with 12 irrigation applications in the second year of the experiment. As a result of the research, the evapotranspiration values measured in the experimental subjects during the plant growing season changed depending on the amount of irrigation water applied between 375,2 and 655,0 mm in 2018 and between 278,2 and 801,3 mm in 2019. Daily evapotranspiration values varied between 1,4 and 8,6 mm day-1 in 2018 and 1,2 and 11,3 mm day-1 in 2019. The sunflower seed yields obtained from the experiment subjects ranged between 272,88 kg da-1 and 503,73 kg da-1 in the first year of the experiment and 222,49 kg da-1 to 518,61 kg da-1 in the second year of the experiment. The seed yields obtained from treatments in both years changed depending on the amount of water entering the soil (precipitation + irrigation). The highest sunflower seed yields were obtained from the experiment where 125% of the evaporation value of open water surface was applied. Water use efficiency (WUE) values ranged between 0,68 and 0,83 kg m-3 in the first year of the experiment and between 0,64 and 0,80 kg m-3 in the second year of the experiment. As a result of the research, it can be suggested that 25 and 50% of the evaporation values measured from the class A pan evaporation is applied under limited water supply conditions. In the under limited water conditions, leaf area index value of 2,86-3,95 m2 m-2, leaf water potential value of -13 and -14 bar, chlorophyll content of 45-50, stomal resistance value of 35-70 mmol m-2 s-1, photosynthesis rate value of 25-30 mmol m-2 s-1 and transpiration rate of 5-8 mmol H2O m-2 s-1 can be used for irrigation applications especially in the flowering period of sunflower.