Response surface optimization of irrigation interval, urea rate, and guar cultivar for maximizing seed yield, biomass, galactomannan yield, and seed oil content

Water scarcity poses a major challenge to guar (Cyamopsis tetragonoloba L.) production in arid regions. This study objectively aimed to optimize the interactive effects of irrigation interval (6, 9, 12 days), urea rate (50, 100, 150 kg ha−1), and cultivar (Brooks, Kinman, Esser) to maximize seed yield, biomass, galactomannan yield, and seed oil content using Response Surface Methodology (RSM) with Box-Behnken Design (BBD). The field experiment was conducted at Vali-e-Asr University research farm (30°23′54″N, 55°59′31″E, 1460 m) during 2023–2024 using split-factorial RCBD with three replications. Seventeen treatment combinations ensured robust model fitting (R2 ≥ 0.98, RMSE < 5%). Optimum conditions identified were: Kinman cultivar with 9-day irrigation + 100 kg ha−1 urea achieving maximum seed yield (4.19 t ha−1, 34% > non-optimized baseline, 25% > prior guar studies) and biomass (8.52 t ha−1, 28% improvement); Esser with 6-day irrigation + 50 kg ha−1 urea maximizing galactomannan (1.02 t ha−1); Kinman optimizing seed oil (0.23%). Multiple-response optimum (desirability = 0.94) confirmed 9-day irrigation + 100 kg ha−1 urea + Kinman.Validation (n = 3) verified predictions (<3% error, p > 0.05), demonstrating 25–35% resource efficiency gains over conventional practices for sustainable guar production.