If you’re wondering how the different air exchange rates influence the growth of cannabis, you’ve come to the right place. This article explores the effects of air exchange rates on the growth of a variety of plants.
Low vs high APPFD
For many growers, selecting a canopy-level PPFD (PPFD) is an important step toward maximizing cannabis yield. In this study, we examined the efficacy of canopy-level PPFDs over multiple time-points during the generative phase of flowering. Specifically, we sought to quantify the relationships between canopy-level PPFDs, leaf-level photosynthesis, and quality attributes. We also assessed the yield-relevant features of the canopy-level PPFD.
To evaluate the canopy-level PPFD’s efficacy, we performed a series of back-calculated total light integrals. These were then aggregated to create a total light integral (TLI) for each plant. Using the average PPFDs from the beginning and end of measurement intervals, TLIs were divided by the length of production time for each plant. The results showed that, despite being smaller, plants grown under a high APPFD were able to produce the same quantity of dry weight as the lower-PPFD plants.
There was an obvious relationship between the canopy-level PPFD and leaf-level photosynthesis. As plants progressed through the flowering phase, the canopy-level PPFD became more uniform. During this period, canopy-level PPFDs ranged from 120 to 1,800 mmol*m-2*s-1. Interestingly, the best TLI for each plant was about 1% of the APPFD.
In addition to the total light integral, we also looked into the effects of a low APPFD. Plants that were exposed to lower APPFDs were more compact and had thinner stems. Similarly, plants that were exposed to higher APPFDs had larger leaves. However, this was not the case for terpenes.
We were particularly interested in the effect of a lower APPFD on the quality of cannabis inflorescences. Typically, inflorescences of the studied variety are dried to a moisture content of 10-15%. A reduction in superfluous tissue and increased ratios of inflorescence to total aboveground biomass increased harvest quality.
Single-leaf photosynthesis
The effect of different air exchange rates (APPFDs) on cannabis growth is an important topic in the industry. While several studies have provided information on the relationship between APPFD and cannabis yield, only a few have studied the combined effects of CO2 and LI.
As marijuana plants transition from vegetative to flowering growth, they are subjected to an abrupt increase in air exchange rate. In the present study, cannabis plants were acclimated to a range of LIs, including low and high APPFDs. This study addressed knowledge gaps in understanding how increasing light intensity affects yield.
Initially, cannabis plants were grown under an 18-h photoperiod. Then, they were acclimated to a 12-h photoperiod. During week 5, measurements were made at different localized photosynthetic photon flux densities (PPFDs). A single datum was used for each plant.
Light response curves were compiled for leaves at various growth stages. Asat, leaf length, and inflorescence density increased linearly with APPFD, while maximum LPPFD decreased. On the other hand, canopy-level PPFDs remained consistent across trials.
Leaf morphology and post-harvest parameters also showed no sensitivity to CB treatment. Rather, the effects were likely caused by self-shading. Moreover, the harvest index increased 1.3 times with APPFD. Interestingly, the harvest index was also associated with apical inflorescence density.
Although the relationship between LI and cannabis yield is predicted to be saturating, it does not meet practical limits of LI used in indoor production. This result implies that the relationship between LI and yield is not a stand-alone gauge. It may therefore be difficult to predict yield based on leaf photosynthesis alone.
The results of this study suggest that increasing apical inflorescence density and LPPFD can improve cannabis yield. However, it is crucial to note that these effects were not found in canopy-level or post-harvest parameters.
Terpenes
A new study aimed to quantify VOC emissions from Cannabis plants grown in four grow facilities in California. This is the first study to provide a detailed profile of VOCs produced by cannabis facilities. The results will provide insight into the capacity of indoor-grown cannabis.
The study also aims to identify future steps in evaluating the contribution of VOCs to air quality. Variation in VOC levels depends on the number of plants, the performance of ventilation systems, and the concentrations of other VOC sources.
The study included a broad range of canopy-level PPFDs, from 130 to 1,238 mmol*m-2*s-1, encompassing a variety of different growing conditions. Photosynthetic parameters showed evidence of acclimation to varying photon flux densities.
Cannabinoid potency and terpene content in harvested inflorescences did not vary significantly with APPFD. However, the total terpene potency did increase linearly with APPFD. Limonene and myrcene were the most common terpenes in harvested inflorescences.
Increasing LI increased apical inflorescence density. Apical inflorescences were larger and had more total dry weight with increasing LI. The yield of inflorescences was also higher. These observations indicate that biomass partitioning from the leaf to the apical inflorescence is shifting.
LI can be used to predict crop productivity, but it is not a stand-alone gauge. For yield prediction, it is necessary to evaluate canopy-level photosynthetic parameters. As a result, the relationship between LI and yield is not saturated.
In this study, cannabis plants were exposed to an enormous variety of PPFDs. They were rapidly acclimatized to a shorter photoperiod after switching from an 18-h photoperiod. Compared to plants grown under the low APPFD, plants under the high APPFD were shorter and had thinner internodes and stems.
EPA approvals for pesticides
The US Environmental Protection Agency (EPA) has made a significant contribution to the hemp industry by approving 10 pesticide products for use on the plant. This is a welcome development as farmers in advance of the upcoming growing season get more assurance about their options for protecting their crops.
While EPA’s approval of the ten pesticides is a big deal, it’s not the only thing happening. For example, a new special permit issued by the federal government is giving states the authority to allow the use of unregistered pesticides to address local pest problems.
Despite the EPA’s recent push to make marijuana production safer, it’s still illegal at the federal level. However, the agency’s latest approvals of pesticides for cannabis growers may open up opportunities to allow safer products onto the market.
When considering which pesticides to use, farmers should consider a number of factors. For example, EPA approved glyphosate, which is used as the main ingredient in Roundup weed killer. It’s an effective herbicide that will help ensure your crop’s health, but it also poses serious threats to human and environmental health.
Other pesticides that have been deemed safe for hemp include atrazine, a widely-used herbicide. These products have the ability to kill off many plants and are often applied to industrial hemp crops.
The EPA’s hemp pesticide approval comes as a relief to hemp farmers who have been unsure about whether or not they’d be able to grow a profitable crop. The agency will continue to review additional pesticides to see if they’re suitable for hemp growth.
The EPA’s hemp pesticide review was a welcome development as farmers prepare for the upcoming 2020 growing season. However, EPA needs to improve its pesticide reviews to prevent unsafe pesticides from making it onto the market.
Environmental impact monitoring
Cannabinoid yield is important from the grower’s perspective. More light will improve yield. However, the optimum light intensity may be limited by practical infrastructure and economics. Hence, it is critical to study the effects of CO2 and LI combined on cannabis yield.
The aim of this study was to investigate the relationship between leaf-level photosynthesis, yield, and canopy-level LI for Cannabis sativa. Cannabinoid yield was measured as the amount of THC produced per plant per growing cycle.
Leaf-level photosynthesis exhibited a dynamic temporal nature during flowering, as indicated in models. However, it cannot be used as a stand-alone gauge to predict yield. Hence, it is crucial to understand the relationship between canopy-level LI and cannabis growth.
In this study, canopy-level photosynthesis was monitored across a wide range of light-permeable photon flux densities (PPFD). Measurements were made at 600-s intervals. Moreover, electrical conductivity was recorded with a Hanna Instruments handheld meter.
Plants were irrigated with a commercial nutrient solution every 2-4 days. Relative humidity was 50 to 65 percent. Nighttime temperature was 25 to 27 degC.
As expected, cannabis yield increased with an increase in canopy-level PPFD. Yield was also boosted by an increase in apical inflorescence density.
However, there were no significant changes in cannabis potency. In contrast, terpene concentrations showed minor differences for each treatment. These results are consistent with previous studies, but they suggest that there are important gaps in the knowledge base regarding the response of cannabis yield to LI.
To improve the quality and consistency of medicinal products, it is crucial to maintain controlled environmental conditions. This requires integration of plant management programs. For example, reducing fungal infection in the phyllosphere and promoting canopy air flow.
