Effects of Agricultural Sulfur and Salicylic Acid on Soil Nutrient Availability and Leaf Nutrient Concentration of Bitter Orange Seedlings under Water Stress

Abstract

Agriculture in Iraq is increasingly challenged by water scarcity, which negatively affects plant growth, particularly evergreen species like sour orange (Citrus aurantium). Agricultural sulfur and salicylic acid are known to improve soil fertility and enhance plant tolerance to environmental stresses; however, their combined effect on sour orange seedlings under water stress has not been sufficiently studied. This experiment, conducted at the Department of Soil and Water Technologies, Al-Mussaib Technical College, during the 2025 season, aimed to evaluate the effects of sulfur application (0, 1000, 2000 kg ha⁻¹), salicylic acid spraying (0, 200, 400 mg L⁻¹), and water stress (50, 75, 100% field capacity) on soil nutrient availability and leaf nutrient concentration. One-year-old uniform seedlings were planted in pots containing a soil–peat moss mixture (1:2). Results showed that the highest sulfur level (S2) significantly improved all measured traits. Water stress at 75% field capacity (W2) enhanced soil nutrient availability, while full irrigation (W3) increased leaf nutrient concentration. Spraying with salicylic acid at 200 mg L⁻¹ (L1) significantly increased leaf nutrient concentrations. Two-factor interactions revealed that S2W2, S2L0, and W2L0 treatments maximized soil nutrient availability, whereas S2W3, S2L1, and W3L1 enhanced leaf nutrient concentrations. The three-factor interaction indicated that S2W2L0 was superior for soil nutrient availability, and S2W3L1 was most effective in increasing nutrient concentration in leaves. These findings highlight the potential of combining sulfur application and salicylic acid spraying under controlled water conditions to improve nutrient dynamics in sour orange cultivation under water-limited environments