The effect of restricted irrigation applications on water-yield relationships in clear field sunflower plant

This study was aimed to investigate water-yield relations of the second crop sunflower plant grown under deficit irrigation applied by drip irrigation method. The field experiment was conducted in the experimental field of Siirt University, Faculty of Agriculture during the second crop sunflower growing season in 2022. The lay out of the experiment was a randomized blocks with split plots and had three replications. One clearfield sunflower variety (C1=P64LP130) and two registered sunflower varieties (C2=P64LL134 and C3=P63MM54) were used in the experiment. The different irrigation levels in the study consisted of full irrigation, where 100% of the water consumed in a 90 cm soil profile every seven days (I100, control subject), and deficit irrigation, where 70% (I70) and 35% (I35) of full irrigation were applied. Yield values varied between 118,89-307,22 kg/ha in all irrigation treatments; 217,26-237,06 kg/ha among the genotype; 117,67-318 kg/ha in genotypexirrigation interaction. Plant height varied between 159,44-170 cm in irrigation treatments; 155-185,44 cm among genotypes; 149,66-191 cm in genotypexirrigation interactions. The CWSI varied between 0,26-0,61 in irrigation treatments, 0,38-0,47 among genotypes and 0.23-0.65 in genotypexirrigation interactions. Stalk thickness, canopy diameter and chlorophyll values were not statistically significant among irrigation treatments and genotypes. The lowest seed yield was recorded in genotype P64LL134 while the highest seed yield was recorded in P64LP130. The lowest yield was obtained under I35 irrigation treatment. The results of the study showed that deficit irrigate in Siirt province can not be recommended for sunflower. If deemed necessary, it is recommended to implement deficit irrigation at a maximum rate of 30% during the initial stage of vegetative development, prior to the flowering. Moreover, non-clearfield sunflower varieties have difficulty in competing with weeds, especially in the early vegetative period, which causes significant yield reductions of up to 40-50%.