Improving crisphead lettuce productivity grown under water deficit conditions through biochar and zeolite soil amendments, coupled with foliar stimulant applications under a drip irrigation system

Crisphead lettuce, among other vegetable crops, has attained significant importance in current times owing to its widespread consumption. Consequently, it is imperative to establish specialized cultivation programs tailored to Egyptian conditions, aiming to optimize productivity and meet the growing demand for these essential crops. So, two field experiments were conducted over consecutive seasons (2022 and 2023) to evaluate plant performance with varying irrigation treatments (100% and 80% of irrigation requirements IR) under the drip irrigation system. The main plots focused on irrigation levels, while the sub-main plots examined the impact of soil amendments (control, biochar at 0.5-ton fed-1 and zeolite at 0.5-ton fed-1). Additionally, sub-sub plots were designated for the application of stimulants, including control (without), arginine (60 mg L-1), melatonin (100 mmol L-1), and a combined treatment (arginine at 60 mg L-1 + melatonin at 50 mmol L-1). This comprehensive approach aims to analyze the combined effects of irrigation, soil amendments, and stimulant application on plant growth parameters and productivity such as fresh and dry weights, leaf area, relative water content, nitrogen, phosphorus, potassium, chlorophyll, carotene, head weight, dry matter, and vitamin C. Also, some enzymatic antioxidants (super oxidase dismutase, peroxidase, and catalyze) and soil properties (available nitrogen, phosphorus, and potassium) were determined. The findings indicated that the application of zeolite and biochar under 80% of irrigation (IR) conditions led to improvements in all studied plant parameters compared to plants cultivated without zeolite and biochar (control) under 100% of IR conditions, with zeolite exhibiting superior effects over biochar. Furthermore, the combined treatment of arginine + melatonin outperformed all other treatments, resulting in maximum values across all studied conditions. Melatonin treatment alone came in second order then arginine treatment alone which ranked higher than the control group (without foliar application). In terms of soil fertility, the post-harvest analysis revealed that zeolite, followed by biochar, contributed to significant improvement. The incorporation of zeolite and biochar into the soil appears to have positively impacted soil fertility parameters, underscoring their potential role in enhancing soil quality and nutrient availability. These findings suggest that both zeolite and biochar can be valuable soil amendments for maintaining or enhancing soil fertility after the cultivation of crisphead lettuce. Also, these results underscore the potential benefits of incorporating zeolite or biochar with soil under reduced irrigation levels and highlight the effectiveness of the combined foliar application of arginine and melatonin in enhancing plant performance.