Nitrogen source and solution strength modulate cannabinoid and antioxidant profiles in medicinal cannabis grown in a deep-water culture system

The optimization of nitrogen nutrition is critical for standardizing the production of bioactive compounds in medicinal Cannabis sativa L. Although deep-water culture (DWC) systems offer precise control over nutrient delivery, the specific effects of ammonium-to-nitrate (NH4+:NO3−) ratios and nutrient solution strength on the phytochemical composition of cannabis flowers remain poorly understood. Notably, this study is the first to jointly examine the combined influence of the NH4+:NO3− ratio and solution strength in a DWC system for cannabis. This study investigated the synergistic impact of different NH4+:NO3− ratios and solution strength on morphological traits, phenolic content, antioxidant activity, and cannabinoid profile in organically grown Cannabis sativa L. flowers in a DWC system. Plants were subjected to varying NH4+:NO3− ratios (20:80, 40:60, 60:40) at full and half solution strengths. Morphological traits were measured at harvest. Methanolic extracts of flowers were analyzed for total phenolic (TPC) and flavonoid (TFC) content, antioxidant activity (DPPH assay), and major cannabinoids (GC-MS). Biomass production was maximized at a 40:60 ratio (full strength) and a 60:40 ratio (half strength). However, the highest TPC, TFC, and antioxidant activity were recorded at a 60:40 ratio under half solution strength, indicating a stress-induced upregulation of secondary metabolites. Cannabinoid synthesis was most favorable at a 40:60 ratio with full solution strength, yielding the highest levels of delta-9-THC (28.46%) and CBD (10.09%). A 60:40 ratio at full strength completely suppressed cannabinoid production, demonstrating acute ammonium toxicity. Cannabis phytochemistry is strongly influenced by both nitrogen form and nutrient concentration. A balanced NH4+:NO3− ratio (40:60) under full nutrition optimizes cannabinoid production, while a high NH4+ ratio (60:40) under nutrient stress enhances phenolic antioxidants. These findings provide a precise framework for tailoring nutrient regimens to selectively target specific bioactive compound classes in medicinal cannabis production.