Enhancing Soybean ( L. Merr) Heat Stress Tolerance: Effects of Sowing Date on Seed Yield, Oil Content, and Fatty Acid Composition in Hot Climate Conditions.

High temperatures can impede the growth and development of soybean plants, resulting in decreased yield and seed quality. Heat-induced damage can be mitigated by adjusting sowing date and selecting genotypes that are suitable for cultivation in hot climates. A 2-year (2017-2018) field experiment was conducted at Safiabad Agricultural and Natural Resources Research and Education Center, employing a split-plot design with three replications. The main plots were assigned three different sowing dates (June 22, July 6, and July 21), while the subplots featured eight soybean genotypes (SF1, SF2, SF3, SK93, M13, SG4, SG5, and Salend) belonged to IV to VI maturity groups. Temperature affected the fatty acid composition across all genotypes. Planting soybeans on June 22 and July 6 resulted in a 16% and 8% decrease in seed yield, respectively, compared to planting on July 21 over 2 years of experiments. SK93 exhibited the highest oil content (25.59%) when sown on the third date (July 21), whereas the SF3 genotype planted on June 22 displayed the lowest oil content (18.68%). Based on our findings, a decrease of approximately 0.33% in oil content and a 0.7% increase in protein content were observed with a one-degree temperature rise from 33°C during the seed-filling period. When the temperature ranged between 36°C and 38°C, the highest seed yield (2665-3008 kg.ha) was obtained, whereas the lowest seed yield (1940 kg.ha) occurred at 41.60°C. Delaying planting led to a higher seed yield (19.72%) and enhanced seed oil content (11.54%). The indeterminate growth genotype SK93 consistently showed the highest average seed yield (3231 kg.ha) over the 2-year experiment, exceeding other genotypes.