Adaptation Strategies for Hemp in Alkaline Salt Environments: Fertilizer Management for Nutrient Uptake and Optimizing Growth

Global soil salinization has become an increasingly severe challenge for agricultural production, particularly affecting the cultivation of economic crops in marginal lands. Industrial hemp (<i>Cannabis sativa</i> L.), despite its economic potential, exhibits a notable sensitivity to salt-alkaline stress, limiting its expansion in saline-alkali regions. This study investigated the regulatory effects of nitrogen (N), phosphorus (P), and potassium (K) fertilizers on hemp growth and nutrient homeostasis under alkaline salt stress. Using a “3414” orthogonal experimental design, we evaluated fourteen NPK combinations under 200 mM NaHCO₃ stress, a concentration determined through preliminary experiments to simulate moderate alkaline stress. Plant growth parameters, biomass partitioning, and mineral nutrient profiles were analyzed after treatment with three biological replicates. The N1P2K2 treatment (N 120 mg·L⁻¹, P 238 mg·L⁻¹, K 348 mg·L⁻¹) significantly enhanced plant performance, increasing shoot biomass by 45.3% and root biomass by 38.7% compared to the control. This optimal combination maintains the K⁺/Na⁺ ratio in leaves above 1.2 and regulated Ca²⁺/Mg²⁺ homeostasis, maintaining a ratio of 2.8–3.2, indicating improved salt tolerance. Notably, excessive fertilizer applications (>400 mg·L⁻¹ total nutrients) exacerbated salt injury, reducing biomass accumulation by 25–30% and disrupting ion homeostasis. Our findings reveal the critical thresholds for NPK application in hemp under alkaline stress and provide practical fertilization strategies for sustainable hemp cultivation in saline-alkali regions.