Impact of hand weeding frequency on agronomic performance and essential oil profile of purple basil (Ocimum basilicum L.)

This study investigated the effect of hand weeding frequency on the agronomic performance and essential oil profile of purple basil (Ocimum basilicum L.) at two distinct ecological locations (Hatay and Malatya, Turkey) during the 2022 growing season. Effective weed management significantly improved key agronomic parameters, including plant height, fresh and dry herbage yield, and dry leaf yield. In Malatya, severe weed pressure (168.5 plants m⁻²) was projected to cause over 80% yield loss in unweeded control plots; however, repeating hand weeding (HW) four to five times successfully mitigated this competition, restoring fresh herbage yields to 45531.2 kg ha⁻¹. In contrast, in Hatay, the maximum fresh herbage yield (47325.6 kg ha⁻¹) was achieved in the weed-free control plots. Regression analysis revealed a strong, positive linear relationship between dry leaf yield and essential oil yield (L ha⁻¹) (y = 0.00703x + 7.59; R² = 0.786). Regarding essential oil composition, linalool (32.76-39.76%) was the dominant compound across all treatments, classifying the population as a mixed "linalool-methyl cinnamate" chemotype. Furthermore, Principal Component Analysis (PCA) demonstrated that environmental factors strongly influenced the chemical profile; Hatay samples exhibited higher proportions of methyl cinnamate, whereas Malatya samples were characterised by elevated eucalyptol and eugenol levels. In conclusion, early and systematic weed management, combined with strategic location selection, is crucial for maximising both biomass production and essential oil yield in purple basil cultivation.