Manure Application and Optimized Planting Density Increase Rainfed Thyme Yields

In a rainfed field study evaluating agricultural management strategies for thyme, researchers found that combining manure application with optimized planting density substantially enhanced both biomass accumulation and essential oil yields in Thymus vulgaris L. Conducted across the 2020–2022 crop years, the agronomic trial tested four distinct cultivars grown under two soil fertility regimes and three plant spacing arrangements. According to the findings published in BMC Plant Biology, biomass production and essential oil characteristics responded strongly to the combined agronomic treatments, with significant differences identified among the evaluated treatment combinations using Tukey’s honestly significant difference test at the 0.05 probability level for most measured traits.

The field trial was structured as a factorial split-plot experiment based on a randomized complete block design to measure the interactions between plant genetics and field management under rainfed conditions. The researchers evaluated two specific fertility levels, consisting of a non-amended control without manure and an organic amendment applied at a rate of 50 metric tons per hectare. Alongside the fertility treatments, the team established three distinct planting densities: a high density of 8 plants per square meter, an intermediate density of 6 plants per square meter, and a low density of 4 plants per square meter.

Across the tested combinations, cultivar 1 established the highest overall productivity when grown under the maximum fertility and density levels. Specifically, when supplemented with 50 metric tons of manure per hectare at a planting density of 8 plants per square meter, cultivar 1 generated a peak fresh yield of 10,362.4 kilograms per hectare and a dry biomass yield of 5,260.6 kilograms per hectare. In addition to high vegetative production, this specific management combination drove essential oil accumulation to its highest levels, producing an essential oil content of 3.46 percent and a total essential oil yield of 182.17 kilograms per hectare, making it the most productive combination identified in the rainfed experiment.

Conversely, treatments omitting manure amendments and maintained at the lowest plant density produced the lowest overall vegetative and oil yields across the experiment. Non-manured plots established at the low density of 4 plants per square meter recorded the lowest fresh yield at 5,339.5 kilograms per hectare, the lowest dry yield at 1,697.1 kilograms per hectare, and an essential oil yield of just 26.24 kilograms per hectare. These comparative metrics demonstrated that rainfed thyme yields experienced sharp reductions in vegetative accumulation and total oil output when grown without organic soil enrichment and under sparse field spacing.

While maximum biomass and volumetric oil output favored higher planting density and manure supplementation, lower crop density favored the accumulation of specific aromatic and phenolic constituents. Cultivar 4 exhibited a distinct biochemical response, yielding the highest recorded thymol concentration of 49.49 percent when supplied with 50 metric tons of manure per hectare at the lowest density of 4 plants per square meter. Cultivar 4 also produced the highest concentrations of p-cymene at 16.54 percent and terpinene-4-ol at 0.44 percent under the experimental conditions, showing that reduced competition among plants fostered greater concentrations of key aromatic compounds.

Different chemical profiles emerged within the other cultivars under varying treatment combinations. Cultivar 2 registered the maximum carvacrol content of 5.37 percent under unamended control conditions without manure at an intermediate density of 6 plants per square meter, while also exhibiting the highest γ-terpinene concentration at 17.26 percent. Principal component analysis and cluster analysis confirmed the results of the mean comparisons, demonstrating substantial differentiation among the four cultivars, manure treatments, and plant densities, and illustrating that while cultivar 1 optimized overall biomass and oil volume, cultivar 4 at wider spacing optimized key phenolic constituents such as thymol.

Subject of Research: Rainfed cultivation of Thymus vulgaris under varying planting densities and manure applications

Article Title: Increasing biomass and essential oil production in four cultivars of Thymus vulgaris L. under rainfed cultivation through optimizing of planting density and manure application

Article References: Chaghaghasemi, F., Safari, H., Yousefi, B., Rahmati, H., & Kahrizi, D. (2026). Increasing biomass and essential oil production in four cultivars of Thymus vulgaris L. under rainfed cultivation through optimizing of planting density and manure application. BMC Plant Biology. https://doi.org/10.1186/s12870-026-10139-y

Image Credits: AI Generated

DOI: 10.1186/s12870-026-10139-y

Keywords: Thymus vulgaris, essential oil yield, biomass production, rainfed cultivation, manure application, planting density, thymol, carvacrol, p-cymene, gamma-terpinene, terpinene-4-ol, dry yield, fresh yield, split-plot design, cluster analysis, principal component analysis