The effect of irrigation intervals and irrigation cut-off time on sesame genotypes yield

agriculture in Iran is the largest consumer of water resources, reducing water availability due to climate change is the most significant limiting factor for agricultural production. Therefore, increasing water productivity and optimising these limited water resources are essential. Considering the constraints on water resources, especially during the summer when sesame cultivation and growth occur in the country, it is necessary to conduct practical studies on optimal water use in sesame farming and the possibility of replacing native varieties and old cultivars with new ones. Hence, it is hypothesised that introducing sesame varieties and lines through reduced plant access to water (increasing irrigation intervals or accelerating irrigation cut-off at the end of the growth period) can achieve greater water use efficiency with minimal seed and oil yield losses. The present research was designed and implemented to address this hypothesis.
The experiment was conducted over two years, 2022 and 2023, at the research farm of the Seed and Plant Improvement Institute, located in Alborz Province, Karaj. The experiment investigated the effect of irrigation intervals, including irrigation after consuming 40% (full irrigation) and 80% (deficit irrigation) of available soil moisture, and the timing of the last irrigation, including irrigation cut-off at the beginning of flowering, irrigation cut-off at the beginning of capsule formation, and irrigation cut-off during mid-capsule formation, on the yield, yield components, oil percentage, and water use efficiency of two sesame genotypes, Ultan and Sesame Line 2. The experiment was laid out in a split-split-plot design )treatment of irrigation intervals as the main plot, the time of the last irrigation as the sub-plot and the genotype as the sub-sub-plot) within randomised complete blocks with three replications. Compound data analysis assuming the random effect of year and using the GLM procedure in SAS software was employed. To compare the means of main effects, LSD test (means statement) was conducted at a 5% significance level, and in case of significant interaction effects, slicing and comparison were performed using the lsmeans procedure (slice and pdiff statements).
Results showed that, in both genotypes, irrigation cut-off at the beginning of capsule formation compared to mid-capsule formation had no significant effect on the number of capsules per plant under full irrigation conditions. The results showed that under full irrigation conditions, there was no significant difference in grain yield between the two irrigation cut-off timings (early and mid-capsule formation). In other words, continuing irrigation after the early stage of capsule formation did not increase sesame grain yield. Additionally, results revealed that although the yield of both genotypes was approximately equal under full irrigation conditions (871 and 890 kg per hecta, respectively, in Oltan and Line 2), the yield of Line 2 was 51% higher than Ultan under deficit irrigation conditions. In Ultan, accelerating irrigation cut-off was accompanied by significantly reducing water use efficiency. In contrast, in Line 2, irrigation cutoff at the early stage of capsule formation not only did not decrease water use efficiency but also insignificantly increased it. In conclusion, it can be inferred that by substituting native masses and old varieties with new varieties and lines in sesame cultivation, savings in water consumption can be achieved, increasing water use efficiency in sesame farming while preventing yield reduction.
In general, it can be concluded that in low irrigation conditions, postponing the time of cutting irrigation until the mid-capsule formation and in full irrigation conditions, cutting off irrigation at the beginning of capsule formation can be a suitable management for sesame production. Also, the replacement of newer cultivars, including the line 2, can be effective in increasing the yield and efficiency of water consumption in sesame cultivation.