Strategic foliar nutrition with Sorbitol, Mannitol, and Boron improves physiological performance and yield in Faba beans on reclaimed sandy soil

Under natural field stress conditions in newly reclaimed sandy soils characterized by extreme diurnal temperature fluctuations (ΔT > 20 °C, peak temperatures 42 °C), limited water retention, and moderate salinity, faba bean cultivation faces significant yield stability challenges. This study evaluated whether combined foliar applications of sugar alcohols (sorbitol, mannitol) and boron could synergistically enhance stress tolerance and yield stability in faba bean under these conditions. A two-season field experiment (2023/2024, 2024/2025) at Sadat City, Egypt, tested three cultivars (Nobaria3, Misr1, Giza717) under seven foliar treatments: control (CK, distilled water), individual applications of sorbitol (40 g L⁻¹), mannitol (40 g L⁻¹), boron (50 mg L⁻¹), and binary combinations (S + M, S + B, M + B) administered at four critical growth stages (30, 40, 50, 60 days after planting) arranged in a factorial randomized complete block design with three replications. Combined treatments demonstrated superior efficacy, with sorbitol + boron (S + B) producing maximum improvements: plant height increased 31% (111.91 vs. 85.38 cm in control, p < 0.01), leaf area expanded 85% (1275.92 vs. 689.93 cm², p < 0.001), and chlorophyll content increased 17% (40.56 vs. 34.78 mg L⁻¹, p < 0.05). The S + B treatment enhanced grain quality with 30.6% higher protein content (31.87% vs. 24.40%, p < 0.001) and 39% increase in 100-grain weight (112.48 vs. 80.67 g, p < 0.01). Nobaria3 exhibited superior treatment responsiveness, achieving peak yield stability of 5.24 t ha⁻¹ (Season 1) and 3.70 t ha⁻¹ (Season 2). Treatment effects remained consistent across contrasting seasons (Season × Treatment interaction was non-significant for 9 of 12 parameters, p ≥ 0.05), demonstrating robust stress-mitigation mechanisms applicable to variable production conditions in newly reclaimed arid lands. The strategic foliar application of combined sorbitol and mannitol enhances osmoregulation, stabilizes cellular membranes, and improves photosynthetic efficiency, thereby ensuring sustained reproductive development. Consistent treatment effects across seasons demonstrate reliable stress alleviation mechanisms appropriate for climate-resilient production systems in newly reclaimed soils.