Introduction and Objective: Since ancient times, humans have recognized medicinal plants as invaluable natural blessings, extensively utilizing them as effective and essential tools for alleviating pain and treating various ailments. Among these, Cucurbita pepo (commonly known as paper-skinned pumpkin) stands out as a highly significant and versatile medicinal plant that has gained widespread application in the pharmaceutical industries of most developed nations across the world. One of the most pressing challenges in modern agriculture is drought, which serves as a critical and limiting factor affecting agricultural production on a global scale. Drought is one of the significant limitations of crop production and productivity in the world. The study of traits related to yield in stress conditions helps to improve the high-yielding cultivars. Yield productivity in developing countries is low due to multiple biotic and abiotic stresses, especially drought. Non-availability of drought-tolerant genotypes in different growth stages is the main limitation in improving medicinal plant productivity in developing countries. Therefore, screening drought-tolerant genotypes at different growth stages can improve yield productivity and high nutrient uptake. In light of the growing necessity to cultivate medicinal plants under such challenging environmental conditions, it is essential to explore strategies that enhance their resilience and productivity. Among various agronomic approaches, the application of nitrogen-based fertilizers and superabsorbent polymers has garnered considerable attention due to their profound impact on plant growth, physiological processes, and overall development. Understanding how these factors influence medicinal plant cultivation is crucial for optimizing agricultural practices and ensuring sustainable production. Therefore, this study was designed and implemented to investigate the interactive effects of nitrogen fertilizer and superabsorbent polymers on the growth, development, and productivity of Cucurbita pepo under field conditions.

Materials and Methods: In order to evaluate the effect of different levels of nitrogen and superabsorbent on nitrogen use efficiency, nitrogen productivity and water use efficiency in paper-skin pumpkin. Field experiment was conducted over two consecutive growing seasons (2013–2014 and 2014–2015) in Kermanshah, Iran. The experimental layout was based on a split-plot arrangement within a randomized complete block design (RCBD), with three replications. ensuring the reliability of results by minimizing variability across experimental units. The main plots consisted of four distinct levels of superabsorbent polymer application: control (no polymer applied), 40 kg/ha, 80 kg/ha, 120 kg/ha. The subplots were designated for nitrogen fertilizer treatments, which were applied in the form of urea at the following rates: Control (no nitrogen fertilizer), 50 kg/ha, 100 kg/ha, 150 kg/ha. The Soxhlet method was used to determine the percentage of seed oil. To determine the fatty acids of the seed, a UNICAM 4600 Gas Chromatograph with a BPX70 capillary column, which is specialized for the separation of fatty acids, was used. Superabsorbent polymers, known for their high water retention capacity, were incorporated into the soil to investigate their effectiveness in mitigating drought stress and improving soil moisture availability. The nitrogen treatments were applied to evaluate their influence on plant nitrogen uptake, growth performance, and yield enhancement. Throughout the experiment, standard agricultural practices such as irrigation scheduling, weed management, and pest control were uniformly implemented across all plots to minimize external influences. Soil samples were collected before the experiment to assess baseline fertility levels. The findings of this study will contribute to a deeper understanding of the synergistic effects of nitrogen fertilizers and superabsorbent polymers, potentially leading to improved agronomic strategies for cultivating Cucurbita pepo in water-limited environments.

Results: The results indicated that seed yield and yield components of Cucurbita pepo L. increased with the application of superabsorbent polymer and nitrogen fertilizer. The highest increases in fruit number per plant, seed weight, seed nitrogen content, and dry weight of leaves and stems were observed with 120 kg/ha of superabsorbent polymer and 150 kg/ha of nitrogen. Fruit weight increased with 80 kg/ha of superabsorbent polymer and 150 kg/ha of nitrogen. However, there was no significant difference between 40 and 80 kg/ha of superabsorbent polymer or between 100 and 150 kg/ha of nitrogen, suggesting that 40 kg/ha of superabsorbent polymer and 100 kg/ha of nitrogen are environmentally and economically optimal. The highest increases in seed water use efficiency, fruit water use efficiency, nitrogen productivity, and nitrogen uptake were observed with 120 kg/ha of superabsorbent polymer and 150 kg/ha of nitrogen. Nitrogen had a strong positive correlation (r = 0.985) with seed yield.

The effects of superabsorbent polymer, nitrogen, and their interaction on oil percentage were significant. At all levels of superabsorbent polymer application, 100 kg/ha of nitrogen resulted in the highest oil content. The interaction of superabsorbent polymer and nitrogen significantly influenced linoleic acid content. The application of superabsorbent polymer provided adequate moisture, promoting proper seed development and increasing fatty acid content. However, excessive nitrogen application reduced oil percentage and fatty acid content. The effects of superabsorbent polymer, nitrogen, and their interaction on oleic acid content were significant, with the highest percentage observed under optimal moisture conditions (120 kg/ha of superabsorbent polymer). A significant effect was also found on palmitic acid content, as increased superabsorbent polymer application, particularly during flowering and seed formation, enhanced palmitic acid levels. Furthermore, a significant effect on stearic acid content was observed, with higher superabsorbent polymer application increasing stearic acid content. The highest stearic acid content was recorded with 100 kg/ha of nitrogen. Nitrogen had the highest direct effect with a coefficient of 0.985 on grain yield. Nitrogen use efficiency with a coefficient of 0.865 had the highest indirect effect through nitrogen on grain yield. Oil had the lowest direct effect with a coefficient of -0.051 on grain yield.

Conclusion: Nitrogen use efficiency showed the highest increase with 120 kg/ha of superabsorbent polymer. There was no significant difference in nitrogen use efficiency among 50, 100, and 150 kg/ha nitrogen applications, suggesting that 50 kg/ha of nitrogen is an environmentally and economically recommended level. Increasing the application of superabsorbent polymer enhanced oil content and fatty acids in Cucurbita pepo L. seeds. The application of 100 kg/ha of nitrogen had a significant effect on oil content and fatty acids.