[spurr]

Originally Posted by statusquo

In regards to this I just have a question: Since lights are off during the 'night' hours and people often run cooling during their 'day' hours, I would assume that the DIF wouldn't be too far from zero ya?

It's usually pretty far from zero, say a day temp (average) is 75'F and night temp (average) is 70'F, that is a DIF of +5 (Fahrenheit). And most people don't keep their temps that close, most people have DIF of +5 to +10.

And are you saying that you could theoretically have higher temperatures (within reason) during the majority of the day as long as you had a few hours that were cool enough (again, within reason) too bring down this average?

Kind of. Using DIF we are most concerned with the early morning temp, not the day temp because it's the early morning temp that effects level of GA3 the most in relation to night temp. So, if a grower uses a DUMP temp of 70'F and a day temp of 75'F and a night temp of 70'F the DUMP DIF will be 0. It's the very early morning temp that matters the most in relation to night temp. If a grower can't lower early morning temp, then the day temp is what they should use to find DIF.

The main reason to use DUMP is to save on electricity and to allow ADT (Average Daily Temp) to stay above 70-70'F, which allows for fastest growth. If a grower can't adjust early more temp (by lowering it) then increasing night temp is the way to go.

[spurr]

Originally Posted by MrFista

Thigmotropism (good touch hehe) results in shorter plants. Shorter plants in limited light environments will increase harvest index. Mechanical stimulation activates a pathway with increased cytosolic Ca++ mediating specific genes which code proteins that affect cell wall properties resulting in physical changes (thigmamorphogenesis). Thigmotropism can be used to advantage to keep plant height down though I have not tested it's usefulness in stretch.

Thigmotropism is like phototropism in terms of plant growth direction, and in some cases shorter plants. However, touching (excessive) also can/does induce SAR, which can make plants stretch and grow more, it's a defense mechanism of plants. Mechanical touching of plants is one method to induce SAR, but it is also used for thigmotropism; the difference is the degree/extent of touching.

For example, if I shook a plant, or rubbed the leafs, or cut off a bunch of leafs, that could/does induce SAR.

Crowding = bad touch. It results in stretch due to phototropic response - shading, not thigmatropic.

Crowding and plant stretch isn't about touching, it's about shading. It think in your latter posts in this thread you make the same point I am making. Crowing increases Red:Far-red ratio intracnoapy and that makes plant stretch more than intracanopy Red:Far-red ratio closer to 1:1.

If the canopy is in the shade (Pfr high) the whole plant will stretch (pre flower example) but once the canopy emerges (Pr elevated) stretch slows and vegetative growth is more normal in ratio to stem growth. Use this to advantage to get fruit and nut trees tall and straight by planting them in shade where they can be in the emergent layer after obtaining height.

It's more about intracanopy than canopy (ex. top of canopy).

This temp differential you speak of - DROP - I think you might pull this off with fans and timers no?

Sure, if you can keep early morning temp close to night temp.

...I was trying to simulate a cool dawn. Did I fluke this drop without knowing why? Never checked temps in there for years since thermometer packed it in.

Sounds like you did! Cool dawn reduces level of GA3 in tissue and that reduces stretch; the closer to the night temp the less GA3, and if dawn temp is below night temp then GA3 is really reduced. But too much of a good thing can be bad, ex. if the DUMP (aka DROP) DIF is -15 (Fahrenheit) for an extended period of time the plant can suffer.

yrs, spurr

[spurr]

Originally Posted by MrFista

Read a couple of the references now to get a feel for it.

Coolio yo!

Thigmotropism is seperated from shading. If anything, I think a crowding thigmotropic response will counteract the phototropic response albeit slightly. Have you checked what the guys are doing with leaf removal to increase yield? This removes some of the crowding effect (but don't do it with finicky plants it'll hermie them).

Why would thigmotropism counteract phototropism? Do you mean if a light is on the left and thigmotropism is done from the right?

I haven't looked into that thread yet, but I assume the increase in yield is coming from induction of SAR due to removal of leafs; and effects upon Red:Far-red ratio allowing to be closer to 1:1 (but that would more effect stretch than yield).

I think removing leafs isn't the best option, there are many other ways to induce SAR, ex. using methylated jasmoic acid, which also increases trich density and number (separately from inducing SAR).

Removing the solar panels for plants isn't the best option IMO...

I drew up a root:shoot life cycle with lots of wee pictures of plants phyllosphere and rhizosphere sizes taking into account pot sizes and events like transplanting, switch to flower, pruning, leaf thinning (senescence too), and resultant change in root:shoot thus hormone ratios... to try and understand what they were doing. Wound up with all sorts of diagrams and arrows and shit - very scientific lol. It helped a bit.

Nice, I'd like to see that. Have you seen this paper:

The Effect Of Container Size
D. Scott NeSmith and John R. Duval
https://www.imok.ufl.edu/veghort/docs...ze_072602a.pdf

As auxin is made in the primordia and young leaves, removal of the shade leaves will not alter the levels of production except in it's role in phototropic response to improved red light. Provided nutrient levels in the medium are balanced with a well balanced nute schedule (or in my case well fed and established microherd); leaf removal may result in a decrease in stretch and subsequent increase in production (via resources channeled to cell division not elongation).

True, and also due to SAR inducement via. removal of leafs which the plant consider an 'attack'.

I imagine a redistribution of water and ionic solutes as the large shade leaves are removed too.

Yup. However, removing large leafs is not the best option IMO. To increase red light intracanopy using a light mover is a good method (ex. for "sunfleck"; which is a short term and not-a-short-term phenomenon). Big leafs not only are the solar panels for plants, but they also allow the plant to fix more Co2, and to carryout respiration at night, etc. The top leafs (ex. apical meristem) is where/how the plant sense temperature, fwiw.

Sorry if that's too off topic. Increasing harvest index is the vehicle we want to construct yes? - might take a few different tools to make it run fast.

No worries . But yes, increasing harvest index is a good goal.

Another aside I thought... you know me... Corn harvest index was increased by getting phenotypes with upright leaves. Denser plantings capturing equivalent light. Some weed strains leaves 'pray' like this. They will catch more light in dense conditions.

See what I wrote about photoinhibition and light saturation in terms of plants praying at top of canopy to reduce photon absorption. I agree that praying could be a good thing to look for if it's a phenotype expression, but not if it's a response to light saturation.

[spurr]

Originally Posted by Dave Coulier

And heres an article in Greenhouse Product News discussing PhotoSelective Greenhouse Films. It has plenty of useful info in there. Even discusses how a high perched water table will increase plant stretch. I know you'll love that part of the article.

Thanks for the link!

[spurr]

Originally Posted by MrFista

AH! Finally with you on the phytochrome mediated crowding response - affects branching and elongation (giberrelin involved?).

Yup, GA3 is a main factor. Same with DIF...

So many variables! I'm drawing out a big assed plant map with hormone origins, travel, destinations etc to try and understand the antagonism and synergy going on. Plant exam yesterday... damn some of those hormone questions... the professors would be hard pressed to answer them... another A though, I owned most of it. Then I got DRUNK and LAID.

Nice, I would like to see that, and good job on the A and the ass!

I have some LAI PPFD-I and RUE reading to do then I'll be able to contribute better to this conversation.

Here are some good papers about LAI, PPFD-I and RUE, taken from the many other papers at this good resource from the University of Guelph "Plant-BIO-3110 Crop Physiology" (link)

Interception of PPFD by a crop canopy

Leaf net photosynthesis

Canopy photosynthesis I (Distribution of Absorbed PPFD within the Crop Canopy)

Canopy photosynthesis II (Whole Canopy CO2 Assimilation)

Canopy photosynthesis III (Canopy Photosynthesis Calculations)

I won't bother reading about 24/7 lighting a plant does most it's growing at night so the answer to that is a no brainer. I am certainly interested in your conclusions on optimal photoperiod.

Don't try to tell some other growers that! I got majorly hated on for stating the same thing as reason to not use 24/7. Also, I read a great study showing plants grow the most during very early morning hours (using a neat tool the measured growth as millimeter per hour), and second most at night. That would make sense considering GA3 increases most in very early morning hours due to DIF.

[spurr]

Originally Posted by VerdantGreen

hey spurr, glad you posted this - i was going to ask you if i could post your reply. too much great info not to share

Cool

also it means that i can tell you about the t5's that ive ordered. the red (narva) tubes peak at 610-620nm and the overall spectrum is 575-650 - with a small amount of far red ish 710. having them mounted on the walls of my cab just above the canopy should hopefully help the light penetrate...a bit more orange than i would have liked but it looks like it will still extend the colour spectrum of the hps a bit more into the red and boost red : far red.

Nice!

p.s. also while we are talking far red i heard somewhere that far-red increases resin production - any comments on that ??

I haven't read anything about it, I will look into it. I think you got that info from someone who didn't do any testing, just looked at the buds, right? By "increaes reasin production" do you mean density of glandular trichcomes (# of trichs per X area?)?

[VerdantGreen]

hi spurr, yes it was a visual report of tric coverage, in a test between 2 led panels. one had had no far red (740nm) whilst the other had a 'standard' amount of far red as part of the 75% or so red in the spectrum. I was told that the panel with far red had more trics and it was 'easily noticeable to the naked eye'. not as scientific as you would like im sure
but it wasnt part of any sales pitch or anything like that - just a conversation between 2 LED enthusiasts.

VG

[VerdantGreen]

also where does blue light come into this? most people seem to think that it's more blue light that keeps plants compact. is this because MH lights actually have a better red;far red ratio?

thanks

VG

[Weezard]

Originally Posted by VerdantGreen

also where does blue light come into this? most people seem to think that it's more blue light that keeps plants compact. is this because MH lights actually have a better red;far red ratio?

thanks

VG

Howzit VG.

Dunno 'bout the MH lights.

The only practical, first hand info I have, shows that changing the ratio between 460nm. and 660nm. has a profound effect upon the internode distance.
This experiment was done with just those two wavelengths.
No far red was added or blocked.
I just "dailed back" the deep red and stopped the stretch like throwing a switch.
The girl with the original ratio kept stretchin' for another 8 or 9 days.

Exact time is a difficult call, but the end result was not.
When I set the ratio back on the first light to finish flowering, the first gal was a foot shorter and stayed that way till the chop.

Not claiming this is science, mind you.
But I do call it a clue that is worth looking into.

Aloha, Y'all

Weezard

[Dave Coulier]

Originally Posted by VerdantGreen

also where does blue light come into this? most people seem to think that it's more blue light that keeps plants compact. is this because MH lights actually have a better red;far red ratio?

thanks

VG

Me and Spurr discussed this awhile back, so I have the answer you're looking for. Metal Halides emit less far-red light than a HPS bulb, so the red/far-red ratio will be more in tune to creating more compact plants.

Ive thought about using MH during the pre-flowering phase to help reduce stretch, but I would be sacrificing some of my DLI by doing so. There are many other ways to control stretch, so its probably not even worth it, but Id like to hear your thoughts on it Spurr.