A COMPARISON OF LIVING SOIL METHODOLOGIES IN RELATION TO PLANT HEALTH AND YIELD IN A CONTROLLED ENVIRONMENT FOR CANNABIS
Abstract: There currently exists many different methodologies for growing cannabis in controlled environments, however there is very little published research on the subject in regards to cannabis cultivation. Conventional approaches using bottled nutrients have a higher cost of production, which has become a challenge cultivators as the market price of cannabis has dropped dramatically. With an estimated revenue of 9 billion in legal cannabis sales in 2017 and estimated revenue of 11 billion for 2018, the emerging market is growing rapidly. Many of the current methods involving hydroponic cultivation have a large carbon footprint and negative environmental impact due to the use of fossil fuels. These methods typically only allow for the media to be used one or two times before being disposed of, which contributes to leaching of phosphates and other nutrients into our groundwater.
The need for more sustainable and earth-friendly methods of cultivation is important from a social perception, environmental, and economic perspective.
Methodology:
For this study an enclosed indoor space was outfitted with three 4’ x 12 ‘ soil beds each containing different organic living soil recipes.
Soil Bed #1: S2S comprised of Peat Moss, Pumice, Compost, Worm Castings, Blood Meal, Feather Meal, Alfalfa Meal, Kelp Meal, Insect Frass, Fish Bone Meal, Bone Meal, Bat Guano, Seabird Guano, Soft Rock Phosphate, Potassium Sulfate, Langbeinite, Greensand, Azomite, Oyster Shell Flour, Gypsum, Basalt Rock Dust, Glacial Rock Dust, Iron Sulfate, Copper Sulfate, Nutrisorb, Fossilized Carbon Complex, Diatomaceous Earth
Soil Bed #2: KIS Organics Biochar Soil comprised of biochar, spaghnum peat moss, fish compost, earthworm castings, volcanic pumice, glacial rock dust, basalt, soft rock phosphate, oyster shell flour, alfalfa meal, fish bone meal, crustacean meal, kelp meal, neem cake, karanja cake, fish meal, feather meal, steamed bone meal, agricultural lime.
Soil Bed #3: XXX Soil Mix comprised of Peat Moss, Coconut Coir, Perlite, African Night Crawler Worm Castings, Composted Porcine Manure, Glacial Rock Dust, Basalt Rock Dust, Oyster Shell Flour, Insect Frass, Fishbone Meal, Certified Organic Alfalfa Meal, Gypsum, Limestone Flour, Bone Meal, Feather Meal, Mined Potassium Sulfate, Blood Meal, Rock Phosphate, Fossilized Carbon Complex, Kelp Meal, Bat Guano/Mineralized Phosphate amended with 10% Biochar and a blend of compost at 2% by volume.
All soil was mixed on-site to ensure accuracy. Each bed was planted with clones containing 1/3 Cookies and Cream cultivar (CNC) and 2/3 Gorilla Glue #4 cultivar (GG).
Environmental Controls:
82F (27.7 C) daytime temperature, 76F (24.4 C) nighttime set point
75rH daytime, 64rH nighttime set point
1500 ppm CO2 set point
Dehumidifiers on 15 minute increment timers so they would turn on 30 mins before lights out.
1000 pfd average at canopy height
Lighting controller would turn off half the lights 15-30 mins before the other half so temp would drop slowly and not spike humidity.
Humidifier on another 15min increment timer so it would turn off 30 mins before lights turned off.
Plants were watered using Blumat irrigation and set to maintain moisture content in the soil at 100 mbar.
Equipment:
Three rolling beds on v-casters and v-track, each 4’x12’.
LED lighting from Fluence Biotechnology (https://fluence.science/). There were 12 VYPRxPlus lights over a 12’ x 12’ canopy with each light covering a 3’ x 4’ footprint. We chose Fluence based on the existing body of research supporting their lights as well as the higher efficiency of LED lighting in comparison to HPS, double-ended HPS and LEC technology.
Two 12k BTU Air Conditioning Units; 200 pint Ideal-Air Humidifier; Atlas 8 Digital CO2 Controller; 2 - 70 pint Dehumidifiers; Helios 12 Light Controller
Soil Testing: We used three types of soil tests to evaluate the nutrient and mineral levels in the media. The Meilich III test and saturated paste test from Logan Laboratories and a Soil Savvy (artificial resin) test from UniBest. The Meilich III test is an acid extraction that is helpful in determining what nutrients and minerals are in the media but it does not show what is currently available for uptake for the plant. The Saturated Paste Tests and Soil Savvy test are two different testing methodologies designed to show what is currently available for plant uptake.
Day 53 of flower
Day 63 of flower
Results:
Yield expressed in lbs. per 16 square feet
| Cultivar | S2S | KIS Organics | XXX |
| Gorilla Glue #4 | 2.13 | 2.76 | 2.65 |
| Gorilla Glue #4 | 2.62 | 3.22 | 2.99 |
| Cookies and Cream | 1.44 | 1.95 | 1.53 |
*Average yield across all cultivars was 2.475 lbs. per 4’x4’ area
Yield expressed in grams per square feet
| Cultivar | S2S | KIS Organics | XXX |
| Gorilla Glue #4 | 60 | 78 | 75 |
| Gorilla Glue #4 | 74 | 91 | 85 |
| Cookies and Cream | 41 | 55 | 43 |
*Average yield across all cultivars was 66.88 grams per square foot
Discussion:
While the overall yields show promise, replication of these trials would be needed to draw further conclusions. Furthermore, based on the soil tests, additional trace mineral applications could have potentially improved overall plant health and yield even though deficiencies weren’t visually apparent.
Soil S2S was mixed using target ranges to match the macro nutrient levels in the KIS Organics soil, however guaranteed analysis on guanos was not reliable and resulted in very imbalanced soil. For future trials it would be pertinent to test the various fertilizer inputs due to the variance in manufacturing and processing.
It is also important to note that soil testing can show variability across laboratories and samples and the goal is not a perfectly balanced soil test but rather healthy plants. The soil test is just a tool to allow us to see potential deficiencies and excesses. In this study we had quite a bit of variability in test results, however there was much less variability that was visible when viewing the plants. This further demonstrates the ability of the plant to regulate it’s own nutrient demand when given traditionally “excessive” levels of nutrients in organic, biologically-active soils.
As we learn more and improve these processes, it seems likely that living soils offer the ability to match or beat hydroponic yields with less input and labor cost, a smaller carbon footprint, and in a manner that would allow for the final product to be certified organic based on current National Organic Program standards.
Citations/Resources:
https://www.slyng.com/news/why-are-so-many-weed-farmers-going-out-of-business-411
https://ktla.com/2018/01/31/u-s-legal-weed-industry-generated-9b-in-revenue-in-2017/
https://www.waterboards.ca.gov/water_issues/programs/cannabis/cannabis_water_quality.html
https://www.oregon.gov/ODA/shared/Documents/Publications/NaturalResources/CannabisWaterQuality.pdf
https://phys.org/news/2017-02-legal-marijuana-sales-escalating-environment.html
https://pubs.acs.org/doi/10.1021/acs.est.6b06343
https://ktla.com/2018/01/31/u-s-legal-weed-industry-generated-9b-in-revenue-in-2017/
