Changes in phytochemical properties and water use efficiency of peppermint (Mentha piperita L.) using superabsorbent polymer under drought stress

Water consumption management and the application of advanced techniques in the agricultural sector can significantly contribute to the efficient utilization of limited water resources. This can be achieved by improving soil texture, increasing water retention, reducing erosion, and enhancing seedling germination through the use of superabsorbent polymers. This study aimed to investigate the effect of Aquasource superabsorbent (AS) on the morphological characteristics, phytochemical properties, antioxidant content, and water use efficiency of peppermint. It was conducted under different irrigation management and using different superabsorbent levels. Therefore, a 3 × 4 factorial design was used to determine the effects of irrigation intervals (2-, 4-, and 6-day) and different levels of AS amount (zero [control], 0.5, 1, and 2 wt%). The effects of these factors on various parameters (morphological characteristics, essential oil percentage, nutrient, protein, proline, carotenoid, antioxidant, and chlorophyll content, leaf area index, relative water content, and water use efficiency [WUE]) were evaluated. The results showed that morphological characteristics and essential oil percentage decreased significantly under drought stress (increasing the irrigation intervals). However, the addition of 0.5 (wt%) AS improved plant growth conditions. Increasing the amount of superabsorbent used to 1 and 2 (wt%) decreased the measured traits, which indicates the creation of unsuitable conditions for plant growth. AS application improved the growth of the root more than the leaf yield of peppermint. A 0.5 (wt%) addition of AS resulted in root length increases of 3, 13, and 15%, respectively, at irrigation intervals of 2, 4, and 6 days, respectively. Additionally, at 0.5 (wt%) AS, root weight increased by 8, 15, and 16% in 2-, 4-, and 6-day irrigation intervals, respectively. Also, the height of the plant increased by 3, 5, and 17% at 2-, 4-, and 6-day irrigation intervals when 0.5 (wt%) of AS was used compared to the control. As well, essential oil percentage increased by 2.14, 2.06, and 1.63% at 2-, 4-, and 6-day irrigation intervals. The nutrient and protein contents decreased as irrigation intervals and AS usage increased, indicating a similar trend. However, compared with the control, the addition of 0.5 (wt%) of AS resulted in some improvements in nutrients and protein. The highest WUE (3.075 kg m^-3) was attained in the 4-day irrigation interval and 1 wt% AS addition. This was followed closely by the 2-day irrigation interval with 1 wt% AS addition at 3.025 kg m^-3, and the 4-day irrigation interval with 0.5 wt% AS addition, which reached 2.941 kg m^-3. Overall, the use of AS in appropriate amounts (0.5 wt%) can reduce water consumption and enhance essential oil yield and WUE in peppermint cultivation in water-scarce arid and semi-arid regions.