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Writer's pictureAshley Manning

NEW RESEARCH! Harvesting Light: The Interrelation of Spectrum, Plant Density, Secondary Metabolites, and Cannabis sativa L. Yield

authors: Philipp Reichel 1,* , Sebastian Munz Jens Hartung and Simone Graeff-Hönninger

Agronomy, Institute of Crop Science, University of Hohenheim, 70599 Stuttgart, Germany;

s.munz@uni-hohenheim.de (S.M.); simone.graeff@uni-hohenheim.de (S.G.-H.)

Biostatistics, Institute of Crop Science, University of Hohenheim, 70599 Stuttgart, Germany;

* Correspondence: philipp.reichel@uni-hohenheim.de; Tel.: +49-711-459-22380



VIDEO SUMMARY




Practical Breakdown

 

This study investigates the morphological, biochemical, and physiological responses of cannabis to varying light spectra with differing red to far-red (R:FR) ratios. Two LED light sources, Solray 385 and AP67, were used, emitting R:FR ratios of 12.9 and 3.7, respectively. The Solray 385 spectrum also featured higher green light emissivity compared to AP67.

A CBD-dominant cannabis variety was grown to examine its responses under these conditions.


The experiment consisted of two parts:

Part one focused on growth dynamics, while part two involved harvesting plants at final maturity to study the effects of a photon flux density gradient. Additionally, plants were cultivated at both low and high planting densities to assess how density interacts with light quality and quantity, influencing yield and secondary metabolite production.


Key findings include a 16% increase in total dry flower yield under the lower R:FR treatment (AP67), with the most substantial gains observed in the last 10 days of flowering.


Plants exposed to AP67 also grew taller (18% increase in height) and had 17% longer side branches compared to those grown under Solray 385. Despite the enhanced yields under lower R:FR light, the Solray 385 treatment resulted in a 41% increase in terpene concentrations.


These findings underscore the significant impact of spectral light quality on cannabis growth and its quantitative (yield) and qualitative (secondary metabolites) characteristics.

Key Findings

 

1.       The AP67 LED light source, with a lower R:FR ratio of 3.7, increased overall dry flower yields by 16%.


2.       The Solray 385 light source, characterized by a 45% higher green light content and an elevated R:FR ratio of 12.9, enhanced total terpene concentrations by 41%. This increase was primarily attributed to a rise in monoterpene synthesis, while sesquiterpene levels remained largely unchanged.


3.       Photon conversion efficiency (PCE) was higher under the AP67 spectrum, achieving 0.06 g mol⁻¹, compared to 0.05 g mol⁻¹ under the Solray 385 spectrum.


 

Application For Cultivators

 

1.       Carefully consider the spectral quality and distribution of your chosen lighting source when cultivating in indoor or light-supplemented environments. It's not just about light intensity; both yield and product quality are significantly influenced by the light's spectral composition and uniformity of distribution across the canopy. Based on this study, cultivators can optimize yields by selecting light sources with high far-red (FR) spectral content and lower R:FR ratios.


2.      Identify and address the limiting factors in your cultivation environment. When using high light intensities, ensure that other critical parameters, such as CO₂ levels, are sufficient to support plant growth. This will help maintain consistently high photon conversion efficiency, effectively translating light energy into valuable dry matter.



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