NPK for Cannabis - recent studies

cobshopgrow said:

most "eye opening" to me is this one (seems my links above are all a bit f... up, sry).

https://www.mdpi.com/1643862

"The improved physiological state under 60–175 mg L−1 K enabled higher biomass and yield production, but K supply above 60 mg L−1 K did not affect yield production (Figure 2). The highest K treatment of 240 mg L−1 K negatively influenced most physiological parameters in DQ compared to the lower K levels, while the cultivar RM did not suffer from excess K supply (Figure 9; Figure S4 Supplemental). K over-supply normally does not induce physiological damage to plants [16,28,49]. Thus, the detrimental effects of high K inputs (at 240 mg L−1 K) on the physiological function of the cultivar DQ were surprising. The adverse effects of K over-supply can be best explained by the substantial reduction in the accumulation of Ca and Mg in the leaves (Figure 7 and Figure 8), as a shortage of Ca and Mg in leaves is a known cause of physiological damage [50,51,52,53]."

maybe some i have overlooked all the years.
sure, its cultivar specific, but seeing especially no benefit on the high THC cultivar in the study is may a hint.

Click to expand...

I've read probably the N/P research paper once upon a time and that was probably the inspiration for me to try heavier N to P ratios.
But as said they didn't really work out as advertised.

As for this research the part I bolded is what I'm sort of thinking aswell.
So pretty high limit for the K to become a problem, and it usually shows as Ca/Mg problems (you know, the ones that people always recommend adding). And importance of the ratio of the 3 to each other, K:Ca:Mg.
But can't find the overall nutrient ratios there, but if your ratios goes all over the place while tweaking one nutrient,
it doesn't yet provide too much to do conclusions on.

Tomatoes are pretty well researched in the past and work pretty similarly as for nutrients they use.
Alot of K research on tomatoes etc.
But in short they seem to enjoy quite a lot of K aswell late in flower.

My experience has been that there is decent uptick on P in the early flower and more K heavy later in flower.

thanks for sharing your experience.
i do also think that the "Cal Mag" problem can be related to your K supply.

"But can't find the overall nutrient ratios there"
me neither, just had another look, cant see any infos given on Ca Mg ratios.
they prob not supplied K as a sole nutirent either, chloride, sulfate etc added also.

in regards of tomatoes, i think i one of the studies is especially mentioned that Cannabis not react as well on K as tomatoes.
and even the numbers may be a bit over the place and cultivars react very different, the trend is quite clear that we prob dont need always levels over 200, or even 300-400ppm, and staying in the lower regions is benefical for the secondary metabolites.
Also too much K might lower the pH too much.

i can not say if thats ideal myself.
my impression is also that you need a luxuary P supply to avoid the plant drawing P when building their seeds, they accumulate P in the rootzone..
Bugbee mentioned it somewhere also, he is also in the 30ppm P is enough fraction, plant dont need it, but plant will try to push a lot P in to its seeds and might draw it from its leaves, sweetspot is to avoid that i guess.

For K i am less sure, also pushed the levels always and am not sure if less is more here, especially at given Mg and Ca supplies and the competition of each 3.

well, long text, my takeaway is only that i will use a organic fertilizer with less K this round and may play with my nutirent ratios when growing organic a bit toward a little less K.
for mineral i may overthink my values there also, pushing K a little less and see if its benefical.
at least avoiding any K tox seems sensefull, especially in regard to Calmag problems, and the competition of K/ Ca/ Mg uptake.
basically, give the plant enough K to fully deliver but not too much to force too low Ca, Mg levels.
idk if raised Ca, Mg levels alter the K tox level of course.

Oh btw. Maxigrow wasnt mine either, used it once and threw it away many years ago.

i tried to get a idea of what ppm you are running.
you wrote "The mix I've been running for the last few years start to finish has been 120-40-180 NPK 90Ca 50Mg 3Fe. I ran 1/4 line" somewhere.
that would be about what the studies say, low P, moderate K.

Yea, that is something along the lines I've used when I had the Maxigro and Maxibloom.
I think I put both of those in some ratio to come close to that NPK 3-1-4 with CaMg 2-1 type of ratio.

But I remember having slight Ca deficiencies before the plant grew better roots.
I blame that mostly on the too much K, since then I prefer vegging with K:Ca closer to 1:1.

I don't pay too much attention to ppm's since I run DWC and go by the EC changes.
But probably in that range still. My tapwater is 0.03EC and at peak growth my nutrient solution is close to 1.3EC with slight downward pressure.

sounds very sane to me.
for what its worth, i also found 120ppm N to be kind of a sweetspot using calcium nitrate, lower in flower.
i did used maxibloom also in a dwc once, ran in to slight Ca problems too using RO water but it did the job well otherwise.
when not using RO i have plenty Ca in the tap.