Impact of four hydroponic nutrient solutions and regrowth on yield, safety and essential oil profile of basil (Ocimum basilicum L.) cultivated in soilless culture systems

Herb production in soilless culture systems (SCSs) requires precise composition of hydroponic nutrient solutions (HNSs) to optimise growth, yield and quality. This study aimed to investigate the effect of four nutrient solutions having different ion concentrations on the yield, quality and safety of basil grown in a New Growing System (NGS®) at two harvest times. The results showed that as ion concentration increased, yield and leaf fresh weight decreased, while total dry matter varied with harvest time. Lower levels of phosphorus and potassium in the HNS increased nitrate concentration in basil leaves, with higher nitrogen specifically increasing nitrate levels, and the second harvest showed the highest concentration in the N12P2K6 (nitrogen: 12 mmol ∙ L−1; phosphorus: 2 mmol ∙ L−1; potassium: 6 mmol ∙ L−1) treatment. This study showed that SCS was successful in reducing the growth of microbial contamination, with the lowest levels of mould and yeast contamination detected in nutrient solutions containing N6P4K12. HNS affected the contents of essential oil compounds such as linalool (the highest amount at the lowest ion concentration) and (E)-α-bergamotene (the highest amount at the highest ion concentration). In conclusion, the quantity, quality and microbiological contamination of basil grown in NGS® depend on the HNS used and harvesting time.