Extended Abstract
1. Introduction: Pepper (Capsicum) is a member of the Solanaceae family, which is commonly classified into two groups: pungent (hot) and non-pungent (sweet). Sweet pepper is botanically known as Capsicum annuum. Bell peppers (Capsicum annuum L.) are a globally significant vegetable, prized for their high nutritional value and their important role in diverse dietary patterns. Bell peppers are a good source of several antioxidant compounds, so consuming a medium number of peppers provides twice the daily requirement of vitamin C. A key factor impacting vegetable quality is the potential accumulation of nitrates and nitrites in edible tissues, with excessive levels being undesirable. Fertilizers are recognized as important nutritional resources for agro-food systems. Unfortunately, the increasing use of chemical fertilizers in recent decades has led to enormous environmental problems. Humic acid (HA) is a natural organic biological fertilizer obtained from organic waste and has a very good effect on plant growth and development. Humic acid (HA), a natural organic fertilizer derived from organic waste materials, plays several beneficial roles in plant growth and development. Amino acids, an organic form of nitrogen, enhance the performance and growth of various plants when applied to the soil or as a foliar spray, directly and indirectly influencing plant physiological activities. Different amino acids have different roles in plant growth, nutrient availability, quality, and plant development.
2. Materials and Methods: This study investigated the impact of effect of amino acid and humic acid foliar spraying on nitrate, nitrite, and some biochemical traits of two greenhouse bell pepper cultivars (Paramo and Taranto). Seven treatment levels were used: a control, humic acid at concentrations of 0.2, 0.6, and 1 g/L, and amino acids at concentrations of 0.5, 1, and 1.5 g/L. Pepper plants were treated weekly for 12 consecutive weeks. Traits such as fruit nitrate content, fruit nitrite content, vitamin C content, total soluble solids (TSS), anthocyanin content, and carotenoid content were measured at harvest. Anthocyanin and carotenoid levels were also measured after 30 days of storage at room temperature. This research was conducted from fall 2021 to spring 2022 in Hormozgan Province, Roudan County, in a commercial greenhouse unit.
3. Results and Discussion: The lowest nitrate and nitrite contents were observed in the Taranto cultivar treated with 0.6 g /L humic acid (52.2 and 3.50 mg/Kg<, respectively). The highest vitamin C (116.1 mg /100 g) and anthocyanin content (3.87 μmol Kg/ FW) were found in Paramo fruits treated with 0.2 g/ L humic acid. The highest TSS and carotenoid content were observed in Paramo fruits treated with 0.5 g/ Lو amino acids. Considering the main effect of cultivar on measured characteristics, the Paramo cultivar exhibited higher TSS, vitamin C, anthocyanin, and carotenoid content compared to Taranto. The findings of this study are fully consistent with the results obtained by Aslani et al (2015) and Ghasemnezhad et al (2011), who stated that the orange (Aracia) bell pepper cultivar had a higher TSS percentage than the yellow (Taranto) and red (Inspiration) cultivars. The highest percentage reduction in fruit carotenoid content during storage was observed in the Paramo cultivar treated with 0.5 g/L amino acid (37.3%), while the lowest reduction was observed in the Taranto cultivar treated with 1.5 g/L amino acid (5%). Similarly, the highest percentage reduction in fruit anthocyanin content during storage was observed in the Paramo cultivar in the control treatment (25.3%), and the lowest in the Taranto cultivar treated with 1 g/L humic acid (9%).In this regard, in the Paramo cultivar, the highest percentage of fruit anthocyanin reduction was observed in the control treatment (25.3%) and the lowest in the 1 g/L humic acid treatment (9.9%). In the Taranto cultivar, the highest percentage of fruit anthocyanin reduction was observed in the control treatment (25%) and the lowest in the 1 g/L humic acid treatment (9%). The results of this study also indicate that the use of controlled concentrations of amino acids in greenhouse bell peppers (0.5 g/L) can help increase the pigment and carotenoid content of the fruit and improve the quality and marketability of the fruit after harvest. In this experiment, the highest concentration of amino acids used also showed the lowest percentage of fruit carotenoid reduction, which indicates the ability of amino acids to increase the internal capacity of the plant to cope with stress conditions in the post-harvest period.
4. Conclusion: The results of this research demonstrate that the concentrations of nitrate, nitrite, vitamin C, carotenoid, and TSS in greenhouse-grown colored bell peppers are significantly affected by foliar applications of amino acids and humic acid. In general, the application of amino acids and humic acid improved the biochemical characteristics of the tested greenhouse bell pepper cultivars. This study provides a basis for developing and improving the quality of agricultural products, promoting the production of healthier food, and enhancing food security.