Closing the Yield Gap for Cannabis: A Meta-Analysis of Factors Determining Cannabis Yield

Abstract

Until recently, the commercial production of Cannabis sativa was restricted to varieties that yielded high-quality fiber while producing low levels of the psychoactive cannabinoid tetrahydrocannabinol (THC). In the last few years, a number of jurisdictions have legalized the production of medical and/or recreational cannabis with higher levels of THC, and other jurisdictions seem poised to follow suit. Consequently, demand for industrial-scale production of high yield cannabis with consistent cannabinoid profiles is expected to increase. In this paper we highlight that currently, projected annual production of cannabis is based largely on facility size, not yield per square meter. This meta-analysis of cannabis yields reported in scientific literature aimed to identify the main factors contributing to cannabis yield per plant, per square meter, and per W of lighting electricity. In line with previous research we found that variety, plant density, light intensity and fertilization influence cannabis yield and cannabinoid content; we also identified pot size, light type and duration of the flowering period as predictors of yield and THC accumulation. We provide insight into the critical role of light intensity, quality, and photoperiod in determining cannabis yields, with particular focus on the potential for light-emitting diodes (LEDs) to improve growth and reduce energy requirements. We propose that the vast amount of genomics data currently available for cannabis can be used to better understand the effect of genotype on yield. Finally, we describe diversification that is likely to emerge in cannabis growing systems and examine the potential role of plant-growth promoting rhizobacteria (PGPR) for growth promotion, regulation of cannabinoid biosynthesis, and biocontrol.

Keywords: GWAS; PGPR; cannabis; chemotype; genomics; light emitting diodes; transcriptomics; yield gap.

Figure 1

Cannabis production in Canada; facilities are numbered by facility size (A). Annual production tends to increase with facility size (B) not yield per square meter (C). It is important to note that it is unclear if facility size is always equal to the area of the cannabis production space. Blue dots are projected yields; orange stars are actual yields and correspond to AB Labs (Facility #5), United Greeneries (Facility #13), MedReleaf (Facility #35), Mettrum (Facility #41), WeedMD (Facility #60), and Canopy Growth (Facility #69). Values are current as of April 2018.

Figure 2

Effect of light type on cannabis yield per square meter. High pressure sodium (HPS) lamps produce higher yields than metal halide (MH) lamps and Super Skunk plants produce higher yields than other varieties when grown under MH lamps.

Figure 3

Effect of the duration of the flowering growth period on yield and THC per square meter. Both yield per square meter (A) and THC per square meter (B) increased with increasing duration of the flowering period. Duration of the flowering period had a strong (|r| > 0.7) negative correlation to maximum temperature and duration of the vegetative growth period; therefore, these predictors have the opposite effects on yield and THC per square meter as duration of the flowering period.

Figure 4

Effect of light intensity on cannabis yield per W and CBD per square meter. (A) Increasing light intensity reduces yield per W and this effect is stronger for most varieties other than Early Pearly and Silver Haze #9, which maintained higher yields at 600 Wm⁻². (B) Varieties other than White Widow produced significantly more CBD at 600 Wm⁻² compared to 400 Wm⁻².

Figure 5

Effect of plant density on yield per W and THC per square meter. Yield per W (A) and THC per square meter (B) declined with increasing plant density. These effects were stronger for White Widow than for other varieties of cannabis. G1 had higher yields per W compared to other varieties at a plant density of 10. Plant density had a strong (|r| > 0.7) positive correlation with maximum temperature during cultivation and a strong negative correlation with the duration of the vegetative photoperiod.

Figure 6

Slow release fertilizer produced higher yields per W compared to the CannaTerra fertilizer regime. When slow release fertilizer was applied, White Berry produced higher yields per W compared to other varieties.

Figure 7

Increasing pot size from 5 to 11 L reduced THC per square meter more for White Widow compared to other varieties.