Sequential foliar NPK nutrition and amino acid supplementation mitigate plant-available water deficit effects on growth, yield, and tuber carbohydrates of potato under greenhouse conditions

Water deficit is a major constraint for potato (Solanum tuberosum L.) production, reducing canopy development, tuber filling, and quality-related carbohydrate accumulation. Foliar nutrition and amino-acid-based biostimulants may partially offset drought-induced limitations in root nutrient uptake and plant metabolic activity. This greenhouse pot experiment evaluated whether a phenology-based, sequential foliar nutrition program and amino acid supplementation can alleviate the effects of progressive reductions in plant-available water (PAW) on potato growth, yield, and tuber carbohydrate composition. Certified seed tubers of cv. Agria were grown in clay loam soil under a completely randomized design with three replications. Pots were maintained at four PAW regimes (100%, 75%, 50%, and 25%), with three foliar regimes within each PAW level: (i) non-sprayed control, (ii) sequential foliar fertilization, and (iii) sequential foliar fertilization plus amino acids. Foliar applications were conducted four times from early vegetative growth to tuber bulking, using stage-specific water-soluble NPK formulations supplemented with micronutrients; the amino acid product was applied concomitantly in the combined treatment. Decreasing PAW reduced stem number, stem diameter, plant length, total leaf number, tuber yield, and tuber carbohydrate concentrations. Across irrigation regimes, sequential foliar fertilization improved vegetative growth and increased tuber yield relative to the control, and amino acids provided a further benefit. Yield responses exceeded changes in tuber number, indicating effects mainly on tuber growth rather than tuber set. Foliar treatments—particularly with amino acids—also increased tuber glucose, fructose, sucrose, and starch within each PAW level, suggesting improved carbon assimilation and/or sink activity under water limitation. Overall, a stage-targeted foliar NPK program integrated with amino acids is a practical strategy to reduce yield penalties and sustain tuber carbohydrate accumulation under deficit irrigation. Field validation across cultivars and mechanistic measurements are warranted to refine dose–timing recommendations.