Effect of Humic Substances On Biomass Production and Constituent Levels In Thyme

Thyme (Thymus vulgaris L.), an aromatic and medicinal plant with antioxidant, antimicrobial, and antifungal properties, is of considerable interest to the pharmacological and food industry.  To determine whether humic substances would affect the growth and bioactive constituent levels in thyme, plants from three companies (Botanical interest^®, Seeds Depot^® and Thyme Garden^®) were grown in plastic pots (500 cc) filled with a greenhouse media (Farfad 3B mix) containing three levels of humic substances.  The humic substances, sourced from HumiSolve USA^® and TM-7 USA^®, were mixed in the dry media at 0, 0.5, 1.0, 1.5, and 2.0 percent.  The interaction of humic substances with soil moisture was monitored by maintaining sets of pots at 20, 40, and 60 percent field capacity.  To promote growth, the plants were fertilized with 50 mL of N-P-K (1 g L^‑1 of 17-5-24) weekly.  Changes in plant growth and development were determined by measurements of plant height, fresh and dry weights, and essential oil content.  Oil constituents were determined by gas chromatography, antioxidant activity was determined using a DPPH assay, phenolic content and flavonoid content were determined using a spectrophotometer.  Results indicate thyme growth and development are affected by humic substances and water content of the growth media.