Effects of soilless cultivation systems, genotype, and Ascophyllum nodosum -based biostimulant on growth, yield, and nutritional quality of water spinach

Water spinach (Ipomoea aquatica Forssk.) is a nutritionally important leafy vegetable suitable for soilless cultivation, yet evidence on the combined effects of cultivation system, genotype, and seaweed-biostimulant concentration remains limited. A greenhouse experiment conducted over two consecutive summer seasons (2023 and 2024) evaluated ‘KUSH Water Spinach’ and ‘Thai Kangkong’ under nutrient film technique (NFT) and substrate-based growing-bag systems with foliar application of an Ascophyllum nodosum-based biostimulant at 1.0, 1.5, and 2.0 mL L−1. Treatments were arranged in a 2 × 2 × 3 factorial completely randomized design with three replicates. Cultivation system, genotype, and biostimulant concentration significantly influenced most traits. NFT improved growth, yield, and nutritional attributes relative to substrate cultivation, while ‘KUSH Water Spinach’ outperformed ‘Thai Kangkong.’ The combination of ‘KUSH Water Spinach,’ NFT, and 1.5 mL L−1 produced the highest numerical yield (34.78 g plant−1), ascorbic acid content (42.92 mg 100 g−1 fresh weight), and earliest harvest (17.22 days after transplanting), although its yield advantage over the 1.0 mL L−1 treatment was marginal (0.19%). Yield was positively associated with leaves plant−1, leaf area index, relative growth rate, and crop growth rate. These findings support optimization of cultivation system, genotype, and biostimulant concentration for sustainable soilless water spinach production.