Nitrogen Fertilizer effects on yield and potency of cannabis

Botany and Cultivation
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Two studies from the University of Guelph on fertilizer rates on cannabis in veg/flower seem to show the limits of nitrogen fertilization return in cannabis. Furthermore in flowering the potency per gram decreased from 21% to 16% following the increasing nitrogen rates. However, the total THC and biomass of flower yield increased with more nitrogen. So my take is for high potency boutique buds feed less and if you’re growing for extract or distillate etc feed heavier to increase total THC/hash yield…

http://hortsci.ashspublications.org/content/52/9/1307.short

http://hortsci.ashspublications.org/content/52/12/1796.short

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I have grown for around 10 years and different strains can have very different abilities to use nitrogen fertilizer. I’ve had strains that will get nitrogen “burn” with half as much fertilizers that i give to other strains. So any evaluation that doesnt take strain into consideration I would remain cautious off cause it can be a huge factor in terms of fertilizer requirements. This piece also just says nitrogen based liquid fertilizer which is very vague and ive grow with two organic fertilizers in the same room on the same strains and they turned out noticeably differently. they grew different (shape) and the buds looked as different as two different strains. that makes me believe that specific formulation of fertilizer has to be taken into account. Biology is fucking complicated and every nutrient effects the absorption and utilization of all other nutrients so when i see something that doesnt treat these as variables i am very skeptical of the ability to infer anything practical from there information

Im confused about what exactly u mean when you say

following in the same cycle on the same plants or on a round of plants that got more fertilizer its whole life? cause all weed loses potency at the end regardless of fertilizer, knowing when to cut is the real trick to growing commercially.

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If you refer to the study they applied a variety of levels of nitrogen fertilizers. As the levels of fertilizer increased they saw a correspondent drop in THC. As the nitrogen increased linearly the THC per gram decreased similarly. Basically the reference from these two studies is that THC per gram % seems to decrease as nitrogen is applied through a dilution effect. It increases tissue weight production faster than it stimulates cannabinoid production. However, the total THC biomass from the same number of plants in the same environment increased meaning a higher number of grams of concentrate or THC isolate could be made from plants grown under a higher nitrogen rate.

While I do agree that cultivars or strains have very different levels of tolerance for fertilizers especially nitrogen I’ve still seen this effect they discuss myself on nearly every variety I’ve grown. I typically experiment with fertilizer rates and have seen correlation as the studies detail. I’d love to see better and more detailed studies done with a larger variety of cultivars. This is the type of work I’m setting up with research licenses in WA state and CA currently.

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Well your work sounds great and cannabis industry sorely need more like it but i think that the extreme variability of strains mean the study of how to maximize “cannabis sativa” gives very little information to someone growing cause it will tell you something that isnt optimal for 80% of the strains they are growing especially since most growers are growing cultivars specifically because they are different and above average.
and I didnt mean to imply I dont think this can happen, as i have also seen it personally in some instances too but scientist have need to eliminate variables sometimes to an unuseful degree. which might confound the truth in this instance because as you give your plant more nitrogen it also needs more of other nutrients and they either gave them nothing but there nitrogen fertilizer or kept all other newts level they didnt specify in the abstract. If something like this was true then it would lead directly to these result cause the production of thc was limited by some unknown factor while growth wasnt. even the slightly more total thc would be explained by this cause the bigger plant had more roots surface area so could absorb more of the fertilizer so it would get slightly more of the limiting factor but not enough to make up for its increased weight. This could mean maybe those bigger plants could have produced proportionally more if cared for “properly”. I have seen how a plant that gets more nitrogen needs more magnesium and calcium first hand with certain nitrogen loving strains cause they got less crystally when “bulking” up near the end. extra calmag the next cycle and it wasnt noticeable the same way. I’ve also had luck replacing calmag with epsom salt with strains that didnt lik the additional calcium from calmag. Obviously i couldnt get test done so i dont think people should trust me without more evidence either but the methodology of this seems flawed to me.

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Repost due to typos:

As someone who has published in ASHS Hort publications and many years of growing cannabis experience, I am happy that people are investigating this, but I just wish different methods would be used.

Using a premixed bottled organic nutrient, then making claims for what is optimal for N without controlling for all of the extra fertilization. This is despite the fact that the authors’ note “To our knowledge, there is no research on flowering-stage fertilizer rates for cannabis.”

Then why start with a single type of organic fertilizer rather than a controlled study using a hand formulated raw salt mixture than can adjust mineral composition individually? I would think that it would be a more accepted method, especially if we’re going to make conclusions about “optimal N rates.”

As mentioned above, the use of a single clonal cultivar is not ideal. I don’t think I’d publish if I didn’t have data across three diverse cultivars. The data generated in this study could lead one to ask questions within the system being worked, but that is the limit of it.

There was another MS thesis outta Canada recently where salt-fed flushed and unflushed plants were compared in hydro or other inert media set up. Then a difference in mineral content or composition in floral tissue was sought but no significant differences across samples was found.
However, they skipped over chlorophyll and protein analysis in the floral tissue. It seems strange they would choose minerals and not proteins to me, because proteins would burn so nasty and would be an obvious target for an accelerated rate of senescence from flushing (which I feel it induces). Chlorophyll is a protein and we can all see the difference in a flushed and unflushed plant next to each other, as well as the difference in burning rate of a flushed and unflushed plant.

I think the issue is too much ‘industry practices’ from the cannabis world being used a starting point. IMO, we should start the other way around, with like Aribidopsis, or other flower or hops protocols, and modify them to apply the thinking from the Cannabis industry, in order to test the validity of the practices from the Cannabis industry. The industry has figured out many things, but many many of the big players are getting things wrong, and it is still, to this day, difficult to find high quality and consistent flowers even in totally regulated markets.

I hope to perform a few studies of my own and publish them in the next year as the resources are becoming available. It costs money to publish though, and at that point you are basically giving free advice to your competitors, which makes an author want to only admit to those truths which are largely insignificant or known

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I also saw the study on flushing and shared that on my instagram. All of these studies are being done at the University of Guelph. I’m in contact with them and some of their students and faculty. I agree these studies are flawed and need to be done differently with more controlled variables and better selection for fertilizers etc. As @Plant2pipe said as well.

I’m not sharing this stuff and trying to say it’s perfect or exactly accurate, but more to start these types of discussions and try to see what effects others have noticed. I

I’m currently seeking a research license in WA for cannabis and the hemp license here as well to continue this type of research. I’ve already got a few projects going with a phD in California. It’s a long, slow process to do good research, but I hope to have some interesting things to share soon. I’ve done my own for over a decade and luckily have been able to test my flower for around the last 7 years as I worked with the Werc Shop in So Cal early. The data I got from changing variables and fertilizer formulas and seeing changes in my cultivation and those of others at the collective I worked for enabled me to see patterns and I’ve patented a few formulas and things that have shown increases in terpenes and cannabinoids in harvested flower. I’m consulting to share the info while our products finish state ag department and EPA approvals.

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That all sounds awesome and i dont mean to come off like im attacking you or this research cause all true data is good data. I just felt like giving my two cent on the topic and experimental design. Im not really in the academic community but have been growing almost 10 years now and i have studied experimental design from both the statistical and physcology frame which may seem unrelated but is all about the minimizing of confounding variables which i feel are abundant in this field.
but im def not claiming to be an expert and glad some real experts are around doing the hard and time consuming research this is gonna take

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I totally understand where you’re coming from. I’ve been a researcher and writer/journalist for a long time. Being edited is a part of life, as is getting peer review. We have to be able to speak openly about errors and ways to improve things without ego if we are to ever improve.

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Firstly, organic nitrogen requires biological activity to be converted into NO3 or NH4. I have actually seen studies on hemp specifically on NH4 that showed the opposite correlation, more NH4 lead to greater THC production, which for hemp growers is undesirable. But there was also strong correlation on available calcium and phosphorus that related to THC production. So just focusing on one element may be misleading, as there could be ideal ratios of nutrients that are offset by more or less nitrogen. Additionally, organic nitrogen while being converted to inorganic nitrogen can be lost or assimilated by various biology instead of the plant itself. There is no proof that a bottle organic nitrogen fertilizer actually increased tissue levels of nitrogen. Were the plants nitrogen deficient to begin with? Hell, you can lose nitrogen to ammonia gas during the nitrification cycle if you don’t have the right biology in your soil. Meaning more organic N fertilizer applied to the soil doesn’t mean more N in the tissue of the plant. And what was the plant doing with the N, was it in excess or was it being metabolized? These are all questions that could be answered if they had also correlated tissue levels of nitrogen and assessed what the plant was actually trying to do with the nitrogen, i.e. storing excess or metabolizing N. Also, what about the C:N ratio? Was there CO2 supplementation, or any carbon in or supplied to the soil? I never feed soluble organic N without some additional carbon at the same time. Cannabinoids are mostly carbon, as is most of the dry weight of the plant. N has to be in balance with C to achieve healthy metabolism and the right biology to digest organic matter, both in the soil and the plant itself. Directly correlating organic N fertilization to THC production isn’t really right, there are so many other nutrient ratios that can influence things. Trace metals like Mg, B, Co, Mo, Ni also relate strongly to nitrogen metabolism in the plant, not just in concentration but in ratios. A deficiency in any of those metals could also slow nitrogen metabolism or assimilation. Just not enough data for me to draw a solid conclusion.

That said, yes, I do agree that excess N levels (among other nutrients) most likely lead to lower cannabinoid production in general. Overfed plants are less healthy and less likely to achieve their genetic potential. Terpene production is related to sulfur levels, for example. Most organic growers and bottled hydro growers that aren’t using collected data to refine fertilization decisions on the spot are way over feeding N and K anyway. So I can’t go by what most people do because most people suck.

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guys dont confuse results of an experiment with scientific fact… those are just the control standards they chose in their experiment… of course the things stated could be a factor but if you have a general healthy plant…

isnt it pretty common sense if you feed heavy N through your flower cycle your flowers wont dense? all they said was THC will be decreased but overall yield will be higher.

the plant will prob be more filled with mad fluffy flowers vs tight cola sites… almost same difference if a flowering plant starts to re-veg and starts fox tailing forever of just tiny tiny flowers…

i could easily see growing a ‘confused’ (traditionally speaking) plant and getting weight of ‘material’ but nothing worth while speaking of traditional flowers that you could trim/dry and smoke

a similar experiment could be to lengthen the light cycle to purposely foxtail your flowers out to try and increase overall ‘material’ yield.

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NO3 has a vegetative hormonal response, while NH4 has a flower triggering hormonal response. This nitrogen signalling comes from the plant adapting to seasonal soil conditions. In the fall, trees and other deciduous plants loose their leaves and begin to decompose. NH4 is released into the top soil during this fall decomposition, causing more NH4 to signal to other plants and microbes that the end of the season is near and winter is coming. So the type of nitrogen matters!

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i was just saying the study is kinda pointless…
we agree that ‘excess N levels (among other nutrients) most likely lead to lower cannabinoid production in general’ i was just saying that doesnt matter if you are growing in chem nutes from north korea or only feed bacterial teas that were prayed over by emerald triangle monks, seemed like a pointless study

but thought it would be interesting if you could grow a plant in a confused state of limbo where it is trying to re-veg but is still producing THC. I have had some experience in the past of flowering plants going back to reveg just turning into huge giant balls of a sticky mess, so i was thinking that could be a good example of an experiment to see how much yield of oil you get on a plant with such characteristics vs a traditionally grown cannabis plant grown for top flower cola sites.

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If you did have a plant in such a ‘confused state’ where it started to re-veg and grew a large mass of fox tails late into flowering, I imagine the trichombes would most likely be at various points of ripening and produce a lower quality oil than from a standard matured plant

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Can you reference a study that alludes to a hormonal relationship to inorganic N type?

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wouldnt various points of ripening mostly effect color? arent most plants going to oil harvested earlier for clear trics? hey man you never know in 20 years a cannabis plant could grow like a true kudzu vine one seed could take over an acre.

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Yeh the darkening color of the trichs is due to the degradation and oxidation of the canabinoids I believe. So this would translate to a darker oil. Yes to my knowledge ppl do pull plants early for oil runs to ensure high THCA content and minimal products of degradation. Although when using supercritical CO2 it is more efficient to extract THC rather than THCA so not sure if they would pull plants later or pull at usual time and decarb before processing

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Some studies report that nitrate signaling is responsible for up to 10% of genomic expression, which is a lot! NO3 vs NH4 ratios, as well as NH4 inhibiting other cations is responsible for a lot of hormonal signaling in plants. Most organic based nitrogen fertilizers are protein/amino based and require biological activity to be broken down first to NH4, and then NO3 afterwards. Only the nitrogen-fixing bacteria, such as Azotobacter, are able to convert atmospheric N2 and O2 into NO3. Azobacter live symbiotically with Lichen. You can harvest Lichen off of rocks and tree bark, and brew a slow aerated tea to get free NO3 from the air.

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You can also use clovers, alfalfa or any other legume as a cover crop to fixate gaseous nitrogen into solid nitrogen compounds :wink: alfalfa also manufactures triacontanol which is supposedly a growth stimulant. I know there has been good research done to show its effectiveness on some crops but as far as I’m aware no research on its specific effects on cannabis. I’ve heard from word of mouth that it can interfere with canabinoid and terpene ratios but I have also heard ppl say some dumb ass things like feeding your plant molasses will give you sweeter buds so who really knows…

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J. Biol. Chem.-2011-Yamada-jbc.M111.269712.pdf (2.3 MB)
Really it comes down to maintaining a good soil ecology.

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Healthy rhyzosphere = healthy plants. I like KNF methods because they are all essentially based of the simple idea that nature can grow plants better than we can so we should observe its processes and use them to our advantage. Let nature do the work for you :wink:

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