A seaweed extract–based biostimulant improves cotton nutrition, physiology, and yield under water scarcity

Cotton ( Gossypium hirsutum L.) production is constrained by water scarcity, and sustainable strategies are needed to improve resilience and productivity. Seaweed extract–based biostimulants (SEBs) are natural materials with the potential to enhance stress tolerance and nutrient use efficiency. This study evaluated the effects of four foliar SEB application treatments on cotton under water restriction: an untreated control (T1), four foliar applications of SEB at early cotton growth stages (T2), foliar application every 15 days (T3), and monthly foliar application (T4) at two sites. SEB application improved macronutrient and micronutrient uptake (K, Ca, Fe, and Cu). It also reduced oxidative damage by decreasing hydrogen peroxide and malondialdehyde contents. Additionally, SEB enhanced water‐use efficiency, carboxylation efficiency, plant height, and productive parameters. Monthly application was the most effective, increasing seed fiber yield by 9.77% (371.14 kg ha − 1 ) and 6.0% (225.0 kg ha − 1 ) compared with the control in the first and second growing seasons, respectively. Monthly SEB application also improved fiber quality by increasing micronaire and reducing the short fiber index. Our findings indicate that SEB application is a sustainable strategy for enhancing cotton nutrition, physiology, productivity, and quality. A monthly application frequency offers a viable approach to maximizing the benefits of biostimulant use in cotton production and contributing to more sustainable agricultural practices.