Foliar Application of Humic Acid and Ascorbic Acid Alleviates Salt Stress in Sweet Pepper (Capsicum annuum L.)

Abstract

Salinity limits sweet pepper (Capsicum annuum L.) productivity in coastal Bangladesh. This study evaluated the comparative effectiveness of foliar-applied ascorbic acid (150 ppm) and humic acid (1200 ppm) in mitigating salinity stress on growth, physiology, and yield of sweet pepper cv. BARI Misty Morich-1. Plants were grown in pots under shade-net conditions and subjected to three salinity levels: non-saline control (0.7 dS m⁻¹ EC, native soil), moderate salinity (4 dS m⁻¹), and high salinity (8 dS m⁻¹), in a two-factor completely randomized design with three replications. Foliar sprays were applied at 15, 30, and 45 days after transplanting. Salinity reduced growth, physiology, and yield (P ≤ 0.05). Both biostimulants alleviated these salt-induced reductions, but humic acid consistently outperformed ascorbic acid. Under severe salinity (8 dS m⁻¹), humic acid produced a substantially greater yield increase over untreated plants than ascorbic acid did. The interaction of non-saline conditions with humic acid (S₀C₂) produced the maximum fruit yield (1170.08 g plant⁻¹), while severe salinity without treatment (S₂C₀) yielded the minimum (311.40 g plant⁻¹). Ascorbic acid was notably more effective in enhancing fruit vitamin C content. Foliar humic acid (1200 ppm) effectively alleviates salinity stress in sweet pepper and offers a practical mitigation strategy for salt-affected regions, though field validation across diverse saline environments is warranted.