Rosemary (Rosmarinus officinalis L.) growth rate, oil yield and oil quality under differing soil amendments

Abstract

In this work, we examined the influence of different soil amendments namely cow manure alone (Cm), cow manure plus fertilizer (Cm þ F), fertilizer alone (F) and unamended check, control on rosemary growth rate, fat content, oil yield and oil quality. Plant height (PLH), number of primary branches per plant (NOPB) and survival rate were assessed at 0, 90, 180, 270 and 360 days after planting during the 2020–2021 growing season. Rosemary plant essential oil and fat content were extracted using steam distillation and Soxhlet methods, respectively, and determined for quality using the gas chromatography with mass spectrometry (GC-MS) method. Plants grown under Cm had a higher PLH and NOPB, whereas the F treatment largely affected the survival rate of rosemary plants than the control. A total of 26 constituents were identified from the obtained rosemary oil grown under different treatments by use of GC-MS analysis with Cm treatment containing the highest number of oil compounds. The main rosemary oil compounds in the present work were alpha-pinene (29.80%–34.34%), eucalyptol (27.15%–30.26%), verbenone (7.63%–8.14%) and geraniol (4.47%–5.22%). The oil yield from the steam distillation method ranged from 0.45% (v/w) to 0.59% (v/w) while the fat content as measured using the Soxhlet method ranged between 11.22% and 13.36% across various treatments. The essential oil yield and fat content from rosemary grown under Cm, Cm þ F, or F conditions were not significantly different. This study shows that Cm markedly influenced rosemary oil quality when compared to other soil amendments.