The Effect of Irrigation and Humic Acid on the Plant Yield and Quality of Sweet Basil (Ocimum basilicum L.) with Mulching Application under Semi-Arid Ecological Conditions

The adoption of suitable irrigation levels (IRL), humic acid doses (HAD) and soil mulching (SM) are important tools for improving the morpho-physiological and biochemical traits of medicinal and aromatic plants. Ocimum basilicum L. cultivated under four IRL: IRL 100 = 100% FC–IRL 75 = 75% FC–IRL 50 = 50% FC–IRL 25 = 25% FC and four HAD: HA 0 = 0.0 Lha(−1)–HA 10 = 10.0 Lha(−1)–HA 20 = 20.0 L ha(−1)–HA 40 = 40.0 L ha(−1) were applied in order to evaluate morpho-physiological and biochemical traits under the ecological conditions of Eskişehir in 2016 and 2017. A second trial was conducted with black plastic soil mulch (SM) and compared with the control plots (CP) in 2016. The experiment was arranged in a randomized complete block design with split plots and three replications. The plant height (PH), fresh herb yield (FHY), dry herb yield (DHY), dry leaf yield (DLY), protein ratio (PR), and main essential oil compounds (MEOC) of Ocimum basilicum L. increased and the essential oil ratio (EOR) and essential oil yield (EOY) decreased with increasing IRL (IRL 100 and IRL 75). FHY (7268.3 and 7472.7 kg ha(−1)) and DLY (635.3 and 637.5 kg ha(−1)) increased with increasing HAD (HA 20 and HA 40) compared to the values of FHY and DLY at HA 0 (6852.6 and 587.0 respectively). The SM application at IRL 50 increased the PH between 8.8 and 13.5%, FHY 11.7 and 16.7%, DLY 22.5 and 29.2%, and at IRL 75 the EOY between 20.0 and 23.9% compared to CP. In addition, PH, FHY, DLY, and EOY were highest at HA 40 and HA 20. The MEOC (linalool, 1,8-cineole, and (E) – β-bergamotene) under SM were more pronounced at IRL 25 and IRL 50 compared to CP. HA particularly improved FHY, DLY, and the main essential oil compounds that can be considered plant biostimulants, which were defined by several studies and regulations.