High Science - Drought stress for better yields?

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Chad.Westport

Chad.Westport

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High Science - Drought stress for better yields?


Publication: American Society for Horticultural Science
Peer Reviewed: Yes
Authors: Deron Caplan, Mike Dixon, Youbin Zheng
Published online: May 2019
Title: Increasing Inflorescence Dry Weight and Cannabinoid Content in Medical Cannabis Using Controlled Drought Stress


Will drought stressing your plant produce larger yields? This study suggests, in part, the answer is yes. Having said that, there may be a few reasons why this particular example is not likely to apply to your grow, and thus potentially returns this topic back to Bro Science territory.

To be clear, we are talking about an increase in cannabinoids, not the dry weight of the flower. The authors of this study are not aware of any other studies of this nature conducted on Cannabis, which makes this study the primary word until a more current test can be conducted.


Why people think it will work;
Drought stress is a major stimulator of secondary metabolites in certain plants. Secondary metabolite accumulation caused by drought stress has been documented in a number of herbaceous species. Drought stress is used to increase oil production in a variety of plants like lemon balm, summer savory, and lemon catmint, to name a few.

Why people argue against it;
Drought stress has been well documented to cause negative impacts on plant growth which in-turn can reduce harvestable plant mass. Drought reduces rates of carbon assimilation (photosynthesis) as a result of both stomatal and metabolic limitations. Under drought conditions, if the soil has salt based nutrients in the root zone, these can become concentrated and create a high soil EC, burning the plants or leading to nutrient lockout.


Specifics of the study
Because science doesn’t view Cannabis as Indica or Sativa, the classification of Drug-Type and Non Drug-Type Cannabis have been used to group different chemovars. Cultivar is the kind of plant (strain), chemovar refers to the chemical make-up (cannabinoids, terpenes, flavonoids etc).
  • Plant type
This study uses a Drug-Type chemovar II plant, which is classified as having a THCa:CBDa ratio generally of 0.5-2.0. Essentially, a four to one ratio, with CBD being the predominant cannabinoid (higher number).
  • Soil type
Test plants were started in a custom mix of 40-45% sphagnum peat moss, 20-25% chunk coconut coir, 20-25% perlite and 5-10% worm castings. When the plants were transplanted into the final 3 gallon container, Pro-Mix HP Mycorhizea was added.
  • Nutrients
Nutrients used in the study were organic from beginning to end, using Nutri Plus Organic, Grow liquid and Bloom liquid, as well as an Organa ADD supplement for micro nutrients and EZ-Gro Inc. Cal/mag.
  • Drought onset and Harvest date
On day 39 of flower, plants were chosen from the control batch to be drought stressed. It took 11 days for the selected drought group to reach the desired drought stress levels. The plant was then watered and returned to a non-drought like state of WP (Water Potential) before being harvested on day 54 of flower.
  • How drought stress was defined and measured
Each plant was equipped with stem psychrometers and data loggers to measure WP every 15 minutes. Capacitance-type substrate moisture sensors were used to measure dielectric permittivity every 15 minutes. This reading was then converted to VMC (volumetric moisture content) using substrate specific calibration.

The selected drought group reached the desired level of drought stress when the WP was approximately 1.5 MPa (drought stress threshold)

***These tools aren’t common in the home growers garden and on a large production scale, not commercially viable. Sensors are costly and require significant technical training.

  • Results
Cannabinoid levels were obtained by using HPLC (High pressure liquid chromatography) which is a common method in State and National testing programs. This study suggests that controlled drought stress can increase the concentration of major Cannabinoids THCa and CBDa. Concentrations increased 12% and 13% respectively.

This was achieved without reducing the dry weight of the harvested drought crop as compared to the control group. This points to the researchers finding the right period of drought insufficient to impede growth, but still crucial to increasing secondary metabolite yield. When measured on a “yield per unit growing area”, overall THCa increased 43%, CBDa 47%, THC 50% higher and CBD 67% higher. This would have major implications for commercial grow facilities.


But please, let me rain on the parade a little;

Where this may differ from your grow

Plant type
Home growers are generally using Drug-Type chemotype I plants, which are classified as a THCa:CBDa ratio of >1-0 (high THC, very low CBD). The authors noted “because rates of cannabinoid accumulation vary by chemovar, the effect of drought on other chemovars should be explored”. They also state, “this study should be applicable for similar varieties of chemovar II cannabis; however, other chemovars or varieties might respond differently”.
  • Soil type
Home growers typically are not using a custom blend like these plants started and developed roots in. Although some home growers may use the Pro-Mix HP product, the soil in this study does not entirely consist of that product. For the sake of argument, lets assume you replicate their soil mix.
  • Nutrients
Home growers who use synthetics have a different biochemistry within their root system. How effectively that responds to drought stress and the secondary metabolite production in comparison with the organics used in this study, the study does not say. One drawback of salt based nutrients in a wet / dry / wet / dry watering schedule is fluctuating EC, which can be the root of many other problems. For the sake of argument, lets assume you are using organic liquid feed.
  • Harvest and drought schedule
Home growers with a true finishing 54 day strain (not extremely common) would need to chose to flush during the final two weeks or to drought stress the plant. The time window used in this study does not allow for both. Peak Cannabinoid levels in this particular chemovar are reached in week seven for THC and week eight or later for CBD. In using Drug-Type chemotype I, which most home growers have, THCa production peaks in week nine and CBDa production in week 11.

• How drought stress was defined and measured

While home growers don’t have those fancy gadgets to measure WP and MPa, there are alternative methods described in the study. Provided there are ideal environmental conditions, leaf angle measurements were an effective indicator of plant stress.

Measurements were made using a protractor or angle finder. At the drought threshold, plants were visibly wilted and the indicator leaf angle increased by 50% from the turgid leaf angle. Measurement was made by measuring the angle between the middle leaflet and the stem from which it originates.


My Summary

This begs the question, do I drought stress the last 11 days, or do I flush in the final weeks? How would this effect the overall taste and burn-ability of the final harvest? If my Cannabis was 20%THC, an increase of 12% would make it 22.5% THC. How significant is that?

Although there was no marginal difference in dry weight between the two groups, photosynthetic activity significantly dropped in the drought group. Would trying a drought period earlier in flower to allow a flush at the end result in less plant yield because the plant has lower photosynthetic activity during the peak plumping periods of week five and week six? This was not tried in the study.

Is the strain they used and the chemovar type representative of all Cannabis plants responses to drought stress? The study specifically points out, that without further research, these results should not be applied to all Cannabis in general. So where does that leave us? We have some support for the idea, but it also raises more questions.

The idea still lands in the zone of bro science to me, because we still only have anecdotal evidence this may work on the types of chemovars most commonly grown by home cultivators and it doesn’t provide any research on how a synthetically fed plant would react to the same stresses. What do you think?


Link to study - https://journals.ashs.org/hortsci/view/journals/hortsci/54/5/article-p964.xml

#ChadWestport #HighScience #CannabisGrowing #TPC
 
High Science edited 5x3 dark
Chad.Westport

Chad.Westport

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Another installment of High Science study reviews. It's one that I see debated a lot on the forums, so I thought I would look a little deeper into the matter. I hope you enjoy it. If you have anything to add, I'm happy to talk more about it and hopefully I can learn more through your experience and research too. Cheers everyone for taking a look. :)

@Aqua Man
 
Chad.Westport

Chad.Westport

554
93
Greenhouse seeds let this tip slip years ago in their youtube strain grow series. It works, no doubt about it!
Haven't seen that, but you know I'm going to hunt it down right now. Thanks for the tip @Dirtbag

I just can't decide which is more important, the flush or the drought. I guess with minimal organics your need for flushing decreases...?
 
B

BroScience101

52
18
Before I made the switch from hydro to organic no till soil I was looking at study after study on yield of no till compared to conventional practices because I was scared of harvesting less but all the studies I came across said yield actually improved.

In particular there was a study on No till corn and wheat production in texas during a drought and the final yield outperformed conventional yields with zero drought.

I also recall coming across no till organic yields on Hops (closely related to MJ) done in salt lake city which also out performed conventional during a season that got a lot less rain than usual.

I may attempt this on my current grow

Here's a generic scholar search with a few studies all showing yield increases in various crops (unfortunately non specifically on MJ)
 
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Dirtbag

Dirtbag

Supporter
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Haven't seen that, but you know I'm going to hunt it down right now. Thanks for the tip @Dirtbag

I just can't decide which is more important, the flush or the drought. I guess with minimal organics your need for flushing decreases...?
The draught. Thats what triggers the flowering response. But the flush before draught is equally important to make sure the ec doesnt spike. And yes, its less important with organics.
 
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Chad.Westport

Chad.Westport

554
93
Before I made the switch from hydro to organic no till soil I was looking at study after study on yield of no till compared to conventional practices because I was scared of harvesting less but all the studies I came across said yield actually improved.

In particular there was a study on No till corn and wheat production in texas during a drought and the final yield outperformed conventional yields with zero drought.

I also recall coming across no till organic yields on Hops (closely related to MJ) done in salt lake city which also out performed conventional during a season that got a lot less rain than usual.

I may attempt this on my current grow

Here's a generic scholar search with a few studies all showing yield increases in various crops (unfortunately non specifically on MJ)
I studied a lot of this in the Sustainable AG program. The thought has always been that the style isn't scalable to massive farms, but as of a few years ago, there are some very large farms doing it this way and yes, they are getting better results already. The problem for most, is that it takes a good 3-5 years to really get the soil to work for you and many of the traditional farmers can't afford the wait. They know the soil has been abused and needs to be fixed, but they also have to get the crop in. Keep with it, what you're doing only gets better with time.
 
Chad.Westport

Chad.Westport

554
93
Thank you for the support, this has traveled far and wide. I love to see the support. Thank you!
 
growsince79

growsince79

7,744
313



High Science - Drought stress for better yields?


Publication: American Society for Horticultural Science
Peer Reviewed: Yes
Authors: Deron Caplan, Mike Dixon, Youbin Zheng
Published online: May 2019
Title: Increasing Inflorescence Dry Weight and Cannabinoid Content in Medical Cannabis Using Controlled Drought Stress


Will drought stressing your plant produce larger yields? This study suggests, in part, the answer is yes. Having said that, there may be a few reasons why this particular example is not likely to apply to your grow, and thus potentially returns this topic back to Bro Science territory.

To be clear, we are talking about an increase in cannabinoids, not the dry weight of the flower. The authors of this study are not aware of any other studies of this nature conducted on Cannabis, which makes this study the primary word until a more current test can be conducted.


Why people think it will work;
Drought stress is a major stimulator of secondary metabolites in certain plants. Secondary metabolite accumulation caused by drought stress has been documented in a number of herbaceous species. Drought stress is used to increase oil production in a variety of plants like lemon balm, summer savory, and lemon catmint, to name a few.

Why people argue against it;
Drought stress has been well documented to cause negative impacts on plant growth which in-turn can reduce harvestable plant mass. Drought reduces rates of carbon assimilation (photosynthesis) as a result of both stomatal and metabolic limitations. Under drought conditions, if the soil has salt based nutrients in the root zone, these can become concentrated and create a high soil EC, burning the plants or leading to nutrient lockout.


Specifics of the study
Because science doesn’t view Cannabis as Indica or Sativa, the classification of Drug-Type and Non Drug-Type Cannabis have been used to group different chemovars. Cultivar is the kind of plant (strain), chemovar refers to the chemical make-up (cannabinoids, terpenes, flavonoids etc).
  • Plant type
This study uses a Drug-Type chemovar II plant, which is classified as having a THCa:CBDa ratio generally of 0.5-2.0. Essentially, a four to one ratio, with CBD being the predominant cannabinoid (higher number).
  • Soil type
Test plants were started in a custom mix of 40-45% sphagnum peat moss, 20-25% chunk coconut coir, 20-25% perlite and 5-10% worm castings. When the plants were transplanted into the final 3 gallon container, Pro-Mix HP Mycorhizea was added.
  • Nutrients
Nutrients used in the study were organic from beginning to end, using Nutri Plus Organic, Grow liquid and Bloom liquid, as well as an Organa ADD supplement for micro nutrients and EZ-Gro Inc. Cal/mag.
  • Drought onset and Harvest date
On day 39 of flower, plants were chosen from the control batch to be drought stressed. It took 11 days for the selected drought group to reach the desired drought stress levels. The plant was then watered and returned to a non-drought like state of WP (Water Potential) before being harvested on day 54 of flower.
  • How drought stress was defined and measured
Each plant was equipped with stem psychrometers and data loggers to measure WP every 15 minutes. Capacitance-type substrate moisture sensors were used to measure dielectric permittivity every 15 minutes. This reading was then converted to VMC (volumetric moisture content) using substrate specific calibration.

The selected drought group reached the desired level of drought stress when the WP was approximately 1.5 MPa (drought stress threshold)

***These tools aren’t common in the home growers garden and on a large production scale, not commercially viable. Sensors are costly and require significant technical training.

  • Results
Cannabinoid levels were obtained by using HPLC (High pressure liquid chromatography) which is a common method in State and National testing programs. This study suggests that controlled drought stress can increase the concentration of major Cannabinoids THCa and CBDa. Concentrations increased 12% and 13% respectively.

This was achieved without reducing the dry weight of the harvested drought crop as compared to the control group. This points to the researchers finding the right period of drought insufficient to impede growth, but still crucial to increasing secondary metabolite yield. When measured on a “yield per unit growing area”, overall THCa increased 43%, CBDa 47%, THC 50% higher and CBD 67% higher. This would have major implications for commercial grow facilities.


But please, let me rain on the parade a little;

Where this may differ from your grow

Plant type
Home growers are generally using Drug-Type chemotype I plants, which are classified as a THCa:CBDa ratio of >1-0 (high THC, very low CBD). The authors noted “because rates of cannabinoid accumulation vary by chemovar, the effect of drought on other chemovars should be explored”. They also state, “this study should be applicable for similar varieties of chemovar II cannabis; however, other chemovars or varieties might respond differently”.
  • Soil type
Home growers typically are not using a custom blend like these plants started and developed roots in. Although some home growers may use the Pro-Mix HP product, the soil in this study does not entirely consist of that product. For the sake of argument, lets assume you replicate their soil mix.
  • Nutrients
Home growers who use synthetics have a different biochemistry within their root system. How effectively that responds to drought stress and the secondary metabolite production in comparison with the organics used in this study, the study does not say. One drawback of salt based nutrients in a wet / dry / wet / dry watering schedule is fluctuating EC, which can be the root of many other problems. For the sake of argument, lets assume you are using organic liquid feed.
  • Harvest and drought schedule
Home growers with a true finishing 54 day strain (not extremely common) would need to chose to flush during the final two weeks or to drought stress the plant. The time window used in this study does not allow for both. Peak Cannabinoid levels in this particular chemovar are reached in week seven for THC and week eight or later for CBD. In using Drug-Type chemotype I, which most home growers have, THCa production peaks in week nine and CBDa production in week 11.

• How drought stress was defined and measured

While home growers don’t have those fancy gadgets to measure WP and MPa, there are alternative methods described in the study. Provided there are ideal environmental conditions, leaf angle measurements were an effective indicator of plant stress.

Measurements were made using a protractor or angle finder. At the drought threshold, plants were visibly wilted and the indicator leaf angle increased by 50% from the turgid leaf angle. Measurement was made by measuring the angle between the middle leaflet and the stem from which it originates.


My Summary

This begs the question, do I drought stress the last 11 days, or do I flush in the final weeks? How would this effect the overall taste and burn-ability of the final harvest? If my Cannabis was 20%THC, an increase of 12% would make it 22.5% THC. How significant is that?

Although there was no marginal difference in dry weight between the two groups, photosynthetic activity significantly dropped in the drought group. Would trying a drought period earlier in flower to allow a flush at the end result in less plant yield because the plant has lower photosynthetic activity during the peak plumping periods of week five and week six? This was not tried in the study.

Is the strain they used and the chemovar type representative of all Cannabis plants responses to drought stress? The study specifically points out, that without further research, these results should not be applied to all Cannabis in general. So where does that leave us? We have some support for the idea, but it also raises more questions.

The idea still lands in the zone of bro science to me, because we still only have anecdotal evidence this may work on the types of chemovars most commonly grown by home cultivators and it doesn’t provide any research on how a synthetically fed plant would react to the same stresses. What do you think?


Link to study - https://journals.ashs.org/hortsci/view/journals/hortsci/54/5/article-p964.xml

#ChadWestport #HighScience #CannabisGrowing #TPC
Drought stress makes hot peppers hotter and improves flavor
 
Chad.Westport

Chad.Westport

554
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Absolutely @growsince79 Peppers are pretty fun to play around with. They need a really warm environment..... geez, if only I knew of a place :)
 
N1ghtL1ght

N1ghtL1ght

187
43
there is also some evidence suggesting that UV-A helps in mitigating the stress from controlled droughts... maybe the effects of UV/blue radiation on root promotion chime in here?
 
Kanzeon

Kanzeon

1,878
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I studied a lot of this in the Sustainable AG program. The thought has always been that the style isn't scalable to massive farms, but as of a few years ago, there are some very large farms doing it this way and yes, they are getting better results already. The problem for most, is that it takes a good 3-5 years to really get the soil to work for you and many of the traditional farmers can't afford the wait. They know the soil has been abused and needs to be fixed, but they also have to get the crop in. Keep with it, what you're doing only gets better with time.

I worked on a 50 acre organic farm that's been using no-till for over a decade. They had the literal best produce that I've ever, ever come across.

Seems like nightshades react well to drought stress in general, since it intensifies the flavor of tomatoes and tomatillos as well as peppers.
 
MIMedGrower

MIMedGrower

17,201
438
I think some drought stress helps weed plants bring out more of well, everything. As I learned to water at a drier and drier point close to just before wilting in peat/perlite mix the plants gave much more smell, flavor and potency and literally twice the yield i was getting when keeping pots on the wet side.

it was hard to wait the extra day to water for best results. I have let quite a few plants wilt learning this.
 
smokedareefer

smokedareefer

1,565
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Back in my day I remember intentionally stressing soybeans by driving over them with a roller at different stages of growth. Government tests have shown an improvement in yield. Just did a search and found this. I farmed in Ontario and 20 years later they are still trying. It was OMAF back then.
 
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Chad.Westport

Chad.Westport

554
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I worked on a 50 acre organic farm that's been using no-till for over a decade. They had the literal best produce that I've ever, ever come across.

Seems like nightshades react well to drought stress in general, since it intensifies the flavor of tomatoes and tomatillos as well as peppers.
That is incredibly awesome. That is a very large patch of land and I would love to visit that one day. Its being done, larger and larger but many farmers still think its hippy dippy new age stuff...... its actually old school man :)
 
RippedTorn

RippedTorn

482
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You'd be wise to ignore studies that focus on thc production. It's such an easy metabolite to produce. Look at all the fukt up hydro with no natural weed smells/flavors/effects: 30% thc.

Seems alot of people stress their seedlings then baby them toward the end. Timing is everything [in organics].Beat your kids when they're adults so they can actually fight back.
 
N1ghtL1ght

N1ghtL1ght

187
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Seems alot of people stress their seedlings then baby them toward the end. Timing is everything [in organics].Beat your kids when they're adults so they can actually fight back.
Lots of what you write here rings true to my xp. Is it perhaps a test of genetics.? by inducing various stresses or outer input, the plant is forced to show new reactions. I, for example, like to repot in veg when the bottom leaves begin to start drooping, so there is already light stress and limitation. But the soilball is then much more light and transplant less stressful and easy. It's, at least, the lesser of two evils when a half-wet rootball would rip apart on attempt.
 
Kanzeon

Kanzeon

1,878
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That is incredibly awesome. That is a very large patch of land and I would love to visit that one day. Its being done, larger and larger but many farmers still think its hippy dippy new age stuff...... its actually old school man :)

Yeah man! Fully organic, intelligent crop rotation, chicken and duck shit for fertilizer, animals that got fed the bruised/broken/rotten produce, and only one tractor. Essentially all of the field work was done by hand- harvesting, pruning, planting, pest control, etc. I credit it with being why I picked up growing cannabis as quickly as I did.

Right after I left they were working on foie gras that's not forcefed. Ducks and geese will overeat on their own if provided a safe patch of land to do it on. Incredible stuff.
 
Chad.Westport

Chad.Westport

554
93
Yeah man! Fully organic, intelligent crop rotation, chicken and duck shit for fertilizer, animals that got fed the bruised/broken/rotten produce, and only one tractor. Essentially all of the field work was done by hand- harvesting, pruning, planting, pest control, etc. I credit it with being why I picked up growing cannabis as quickly as I did.

Right after I left they were working on foie gras that's not forcefed. Ducks and geese will overeat on their own if provided a safe patch of land to do it on. Incredible stuff.
Hek yeah man, you totally get it. That would have been a rad experience out on that farm. Thanks for sharing that Kanzeon :)
 
Dirtbag

Dirtbag

Supporter
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I think some drought stress helps weed plants bring out more of well, everything. As I learned to water at a drier and drier point close to just before wilting in peat/perlite mix the plants gave much more smell, flavor and potency and literally twice the yield i was getting when keeping pots on the wet side.

it was hard to wait the extra day to water for best results. I have let quite a few plants wilt learning this.

Yep dry cycles are super important with soil or soiless mixes. I know several growers that utilize drought stress even in highly fertigated mediums like rockwool and coco to cause an explosion of growth in the 3rd and 6th week of flower.
 
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