Optimal Marijuana Crop Growth Using Gas Sensing

marijuana for medicinal purposes

Image Credits: Ryland zweifel/shutterstock.com

Marijuana sales have become big business since the legalization of marijuana for medicinal purposes in 33 US states1 and Canada2. The 2020 US retail sales are estimated to continue growing rapidly from $15.7 billion to $19 billion3, and suppliers will struggle to keep up with this increase in demand. In 2014, legal demand in Colorado alone was exceeding 100 metric tons per year.4 This means that there is a strong incentive to improve the yields of marijuana crops as well as the growth process efficiency.

Marijuana grows similarly to many other crops, with plants typically favoring light, humid and relatively warm conditions.5 Strains of marijuana are chosen because of their tetrahydrocannabinol (THC) content. Generally, products labeled as ‘hemp’, such as rope and oils, are derived from low THC products. Those plants with higher THC content tend to be grown for recreational use.

Improving Yields

Using modified atmospheres is a popular way to improve crop yields.6 This involves growing crops in an atmosphere that has been changed deliberately to control the concentrations of certain gases. This method is commonly used to help improve crop quality7 and as a way of preserving products during transportation8, as well as to improve food growth. One of the most effective gas concentrations to alter to help with crop growth is carbon dioxide.

Carbon dioxide is an important chemical foodstuff for plants. This is because, in the presence of sunlight, the plant combines water and carbon dioxide, to produce sugars and oxygen. This process is called photosynthesis. The sugars can either be used as a source of energy, or converted into other chemicals like chlorophyll, a building block of plant growth. The oxygen is released back into the atmosphere so that it is available for all other life on Earth.

It has been shown that elevated carbon dioxide concentrations can increase crop yields.9 For crops such as legumes, the leaf growth rates and overall biomass can be enhanced with the use of specific carbon dioxide concentrations. However, it was also demonstrated that too much carbon dioxide results in detrimental factors, including reduced seed growth.10

This is also true for marijuana plants. Increased CO2 levels were shown to help growth time and rooting time for clone plants as well as overall plant health by helping to make plants that are healthier and more resistant to infection.11

Balancing Act

There is such a thing as too much CO2. In excess CO2 levels, dark spots appear on leaves and, in extreme cases, the plant dies. For marijuana plants, the optimum levels are thought  to be between 1200 – 1500 ppm, and this means that the gas compositions need to be carefully controlled.11

Ideally, this control needs to be automated because high levels of CO2 can be harmful to humans. In conjunction with an online, continual monitoring sensor system, this means that growing conditions can be controlled at all times, without needing additional human involvement.12

Automated Solutions

Automated solutions such as these for greenhouses need highly sensitive, accurate gas monitors that can be used for continual online monitoring. Edinburgh Sensors are experts in the development and production of non-dispersive infrared sensors (NDIR).13 Edinburgh Sensors offers a range of products suitable for online logging of carbon dioxide concentrations and the possibility of integrating into feedback systems for online gas control. This provides a range of solutions for improving the marijuana plants’ crop yield.

The Guardian NG14 and Gascard NG15 are suitable sensors for installation in a greenhouse for active online monitoring. Both devices retain the accuracy of ± 2% over the full range of humidity conditions (0 – 95%) that plants are likely to be grown in. The Guardian NG comes in a convenient format with on-screen controls and logging. The Gascard NG also comes in the Boxed Gascard16 variant and this includes housing for easy integration and installation.

Gascard NG

Gascard NG. Image Credit: Edinburgh Sensors

Edinburgh Sensors offers full technical sales advice both pre- and post-purchase on all products as well as guidance on interfacing NDIR sensors with data logging or control systems. The Guardian NG and Gascard NG have R323 connectors onboard or optional Ethernet support. The Boxed Gascard also has a USB option. Additionally, the Guardian NG can be used to read faults or issues from other devices it is interfaced with.

The Guardian NG is capable of CO2 detection between 0 and 3000 ppm. This makes it ideally suited to the ranges used for plant growth. If necessary, variants of the Gascard NG can detect up to 5000 ppm. Both devices provide excellent accuracy and boast very short warm-up and response times. This means that they can easily detect sudden or small changes in gas concentrations. The extensive built-in temperature compensation ensures their robustness, and the gas detection remains accurate over a wide range of environmental conditions.

References and Further Reading

  1. State Marijuana Laws (2019), http://www.ncsl.org/research/health/state-medical-marijuana-laws.aspx
  2. Canada Cannabis Legality (2019), https://www.justice.gc.ca/eng/cj-jp/cannabis/
  3. Retail Marijuana Sales (2019), https://mjbizdaily.com/exclusive-us-retail-marijuana-sales-on-pace-to-rise-35-in-2019-and-near-30-billion-by-2023/
  4. Colorado Department of Revenue Report (2014), https://www.cannabisconsumer.org/uploads/9/7/9/6/97962014/market_size_and_demand_study_july_9_2014[1].pdf
  5. R. C. Clarke, “Marijuana Botany: An Advanced Study: The Propagation and Breeding of Distinctive Cannabis”, (1981), Ronin Publishing
  6. Correct Gas Concentrations for Atmospheric Packaging, (2018), https://www.azosensors.com/article.aspx?ArticleID=1012
  7. Streif, J. et al. (2016). Production of Volatile Aroma Substances by ‘Golden Delicious’ Apple Fruits after Storage for Various Times in Different CO2 and O2 Concentrations Journal of Horticultural Science 63 (2): 193–99. https://doi.org/10.1080/14620316.1988.11515847.
  8. Giovannoni, J J,. (2001) Molecular Biology of Fruit Maturation and Ripening. Annu. Rev. Plant Mol. Biol. 52: 725–749.
  9. Wittwer, S. H., & Robb, W. M. (1964). Carbon dioxide enrichment of greenhouse atmospheres for food crop production. Economic Botany, 18(1), 34–56. DOI:10.1007/bf02904000
  10. Vara Prasad, P. V., Allen, L. H., & Boote, K. J. (2005). Crop Responses to Elevated Carbon Dioxide and Interaction with Temperature. Journal of Crop Improvement, 13(1-2), 113–155. DOI:10.1300/j411v13n01_07
  11. Maximizing Yield (2019), https://www.maximumyield.com/the-missing-ingredient-co2/2/1214
  12. Automated Greenhouses (2019) https://www.priva.com/uk/solutions/horticulture/greenhouse-automation
  13. Edinburgh Sensors (2019) https://edinburghsensors.com/about/about-us/
  14. Guardian NG (2019) https://edinburghsensors.com/products/gas-monitors/guardian-ng/
  15. Gascard NG, (2019), https://edinburghsensors.com/products/oem/gascard-ng/
  16. Boxed GasCard (2019) https://edinburghsensors.com/products/oem/boxed-gascard/

This information has been sourced, reviewed and adapted from materials provided by Edinburgh Sensors.

For more information on this source, please visit Edinburgh Sensors.

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