Effects of humic acid and proline on soil nutrient availability and yield of sweet pepper (Capsicum annuum L.) under salinity stress in greenhouses

Abstract

The goal of this research was to assess the effect of humic acid (HA) applied to the soil and foliar sprayed with proline (Pro) on the growth and yield of sweet peppers, Capsicum annuum L., cv. Carisma F1, and soil fertility (N-P-K) at 2 different irrigation water salinities (1.5 and 3.5 dS m⁻¹) in a field study conducted in a plastic greenhouse in the fall of 2024 using randomized complete block design (RCBD) and 3 replications of each treatment. The experimental treatments consisted of 3 levels of HA (0, 8 and 16 kg ha⁻¹), 3 concentrations of Pro (0, 50 and 100 mg L⁻¹) and 2 irrigation water salinity levels (1.5 and 3.5 dS m⁻¹). The results of the study indicated that 16 kg ha⁻¹ of HA significantly increased N, P, K, and organic matter levels of available soil by 36.60%, 66.36%, 63.86% and 9.86% respectively, when compared to the control (no HA applied). All three nutrients increased significantly (N by 27.68%, P by 48.00%, and K by 36.89%) under treatment using the same method. Proline applied at 100 mg /L had an effect on soil nutrient availability and leaf nutrient concentrations that resulted in total yields being greater than control by 9.37%. The (3.5 dS/m) salinity stress level produced a substantial decrease in measured parameters; however, it did produce an approximately 107.5% increase in leaf proline content as a indicator of stress response. The HA + Pro combination (H₂P₂) produced synergistic effects, producing a total yield of 59.92% greater than control. The triple interaction (H₂P₂S₁) produced the highest values of all parameters. These results indicate that combining humic acid and proline can effectively reduce saline stress and improve the productivity of sweet pepper by improving soil and plant nutrient status.