Fertilizer experiment and calculations

[ALToronto]

I'm going to do a mini-trial on fertilizer comparison. I've just deflasked a novelty phal that I'm willing to experiment on. There are about 50 plants that I would consider viable, and probably twice as many 'runts' that have a very slim chance of survival. Still, I have put them all into sphag compots, and each compot has both viable plants and runts. Photos attached. I ended up with far more plants than I expected, and I ran out of plastic containers. So another variable is the container - there are four net pots in addition to the plastic.

I have on hand only two fertilizers - K-lite and Dyna-Gro Grow (7-9-5, 2Ca - 0.5Mg). I may also add a fish fertilizer (Neptune's Harvest, 2-3-1). I plan to use KelpMax with K-lite and DG; the fish fert already contains seaweed. Here's where I need advice. I plan to feed the inorganic ferts at the same N dosage - so for freshly deflasked seedlings, what should that dosage be? So far, they've only been fed KelpMax (I soaked the sphagnum in about 1:125 concentration).

Question 2: I think I should adjust Ca and Mg in the DG fertilizer so that it matches K-lite. I have CaNO3 and epsom salts - so how much of each should I add? I have a 4000 ppm N concentrate for K-lite; I plan to create the same for DG. Of course, adding CaNO3 will also increase N, correct? So the question remains, how much should I add? And where Ca and Mg % are shown on the label, is that for elemental Ca and Mg, or for some compound that includes another element (and therefore has a different molecular weight)? I know that these calculations have been discussed already in other threads, but I don't have time to go back through the 400+ posts in the K-lite thread to find them. So please, let's repeat them in a dedicated thread.

If someone wants me to test out another fertilizer, I'm happy to add it. I have enough compots to accommodate 4 different products. Please put about 50 grams in a double ziplock baggie and mail it to me. You can PM me for my address. Your fertilizer should be significantly different from the ones I am already using.

I don't want to do a 'no fertilizer' control - if anything, that will be the fish fert. I'm not prepared to deliberately lose any plants, but I am willing to have different growth rates. The metrics will be change in the no. of leaves, leaf span and no. of new roots in selected plants in each compot. Now time to criticize my goal and methodology.

 

[Stone]

Just a suggestion AL, but wouldn't it be better to leave out the kelp if you are tryng to compare the fertilisers? The addition of kelp may totally compromise your efforts to discover the best combination of macro elements by stimulating growth in unknown ways.
Maybe it would be more instructive to make seperate trials with and without the kelp?
What form of N is in the dynagrow?

 

[Rick]

In the good old days folks used MSU at the same rate for their seedlings as their adult plants. 100ppm N weekly in RO water. That supplied over 100ppm K at the same time.

The K is already reduced relative to N in your alternate fert choices so not sure if you are really doing anything different than two low K trials, except in this case the Ca and Mg are less than the K concentrations. If you are using something other than pure water to make up your fert, and or watering, then you will supply ample soluble Ca and Mg to make up for the lack in the fert.

A combination of the dynagro with the fish emulsion in a moderately hard dilution water is pretty much the same as K lite with kelp in RO water.

So need to know what the goal of your trial is to figure out what to do with these ferts.

 

[ALToronto]

I'm using RO water, about 12 ppm. So I guess I should get some MSU as well. Anyone care to donate a small amount?

Is anyone still feeding 100 ppm N? I thought everyone backed off to 30-40 or so, even less. My seedlings are indoors, in a mini terrarium (I removed the lid for the photo).

My goal is to determine the effects of reduced P and K, keeping other macro nutrients as similar as possible. That's why I want to adjust Ca and Mg. Mike, if I didn't care about the plants, I would omit the KelpMax, as you suggested. But I do care, so even though it may confound the results, I will continue to use it.

 

[Rick]

If your goal is to compare reduced K and P to a high K and P formula, then you need to use some basic balanced feed or the old MSU formula. Your present choices already are moderately reduced K (especially if you are only going to feed at 20-30ppm N).

If you wanted to test K an P specifically then take K lite and add increasing amounts of K2SO4 and monopotassium phosphate.

 

[ALToronto]

I'm reluctant to use 'a basic balanced feed' because of insufficient micronutrients and urea-source N. I do want to use premium products that are formulated for orchids.

I do not have access to individual chemicals other than calcium nitrate and mag phosphate.

 

[mormodes]

Since you are talking about Phals check these articles:

http://www.hrt.msu.edu/faculty/Runkle/Orchid/Articles/Growing_the_Best_Phalaenopsis_Part_1.pdf

http://www.hrt.msu.edu/faculty/Runkle/Orchid/Articles/Growing_the_Best_Phalaenopsis_Part_2.pdf

http://www.hrt.msu.edu/faculty/Runkle/Orchid/Articles/Growing_the_Best_Phalaenopsis_Part_3.pdf

http://www.ecaa.ntu.edu.tw/weifang/lab551/flower/phal/gg200510pp86-89orchids.pdf

http://marrero3.tripod.com/katia/fertilizer.pdf

 

[Rick]

Thanks Mormodes. We've seen some of these before.

The last paper is particularly interesting to me since it shows how crazy you can make a study and not have anything to show for it.

6 different ferts fed at 2 different concentrations (12 treatments), and all 12 treatments did about the same.

All 6 ferts are pretty much the same (all high K). The pots were heavily amended with lime and micros. Local municipal water was used instead of RO. There were never any treatments at ecologically relevant levels of nutrients (although hybrid Phalaes) are not ecologically relevant in and of themselves.

But note that all the articles are for optimizing short term production. The studies don't go beyond a growing season. Pot management and disease control are considered as separate management subjects from feeding, and a cost to maximizing profit to getting plants to sales distribution.

 

[naoki]

I agree with Rick's comment in message #5. If your hypothesis is that reduced K (and/or P) improve the growth, isn't it better to control only one aspect? So K-Lite vs K-lite + additional K (maybe with KOH, but you need to adjust the pH). You can buy KOH from ebay (and maybe use white vinegar to adjust the pH). Or it may be available in a hydroponics store (since it is used for the electrode of pH meter and as the storage solution).

With 50 plants, you can probably have only 2 (or possibly) 3 treatment groups. With compots (instead of planting each individual in each pot), if you want to take into account the correlated environment due to the shared media/pot (i.e. a random blocking factor in linear mixed-effect model), you may need to stick with 1 simple hypothesis of only 2 groups.

 

[ALToronto]

Thanks Mormodes, I've read all those articles and found nothing useful in them. All the trials were at absurdly high concentrations and had different objectives. A commercial grower wants only the strongest plants to survive and get to bloom as quickly as possible. I want as many plants as possible to survive and grow, and I'm more concerned about longterm health than quick gratification.

I'm going to change my hypothesis. Instead of isolating effects of individual nutrients, I'm simply going to compare 3 different commercially available fertilizers while adjusting Ca and Mg to the same concentration for all 3 ferts. It had been suggested that perhaps the apparent success of K-Lite was due to higher Ca and Mg amounts, so I will test that out.

 

[Rick]

It had been suggested that perhaps the apparent success of K-Lite was due to higher Ca and Mg amounts, so I will test that out.

No, actually the success of K lite is expected due to reducing K to ecologically relevant concentrations so that leaf tissue concentrations of Ca and Mg are allowed to approach normal levels found in wild plants.

There is lots of work demonstrating that plants (not just orchids) will uptake K to the detriment of Ca and Mg, even when high concentrations of Ca are available (for instance the Cornell work done in the 1970's)

The question should be whether or not orchids with high K:Ca ratios in leaf tissues do worse/better than plants with low K:Ca leaf tissue ratios. That seems to be the area of greatest debate.

A definitive, universal external K concentration that produces the above low K:Ca ratio has only been inferred from scant ecological literature values. I suspect it will vary among species as does toxicological tolerance to K varies among animal species. But referring again to the Cornell work, it must be less than 50 ppm K, since that was the lowest K dose (against a constant Ca dose of 200ppm) used on 3 genera of orchids, and all leaf tissue concentrations still ended up with more K than Ca and Mg. So we still don't know if feeding K lite at 100 or 50 ppmN weekly will get the appropriate ratios (although its pretty obvious that the nature of the plants leaves are noticeably different on a low K diet).

Leaf tissue studies are routinely performed to the public by any good County Agriculture Extension service. I haven't checked on price and the amount of leaf tissue required to do this analysis, but comparable soil analysis is only around $20 dollars a sample. Unfortunately you may need to sacrifice an entire seedling to get enough sample to test, but it appears that only single leaves or parts of leaves of bigger plants were needed for other leaf tissue based trials (like the Zotz bromiliad trial).

 

[Stone]

(although its pretty obvious that the nature of the plants leaves are noticeably different on a low K diet).

In what way?

 

[ALToronto]

I can still include the MSU fert in this trial, but I don't want to buy it. If someone wants to send me 50 g, I will gladly accept the donation.

 

[Rick]

In what way?

In several collections leaves are bigger, stiffer, shinier.

 

[Rick]

Is anyone still feeding 100 ppm N? I thought everyone backed off to 30-40 or so, even less.

Feeding 100ppm N weekly was pretty much SOP before bringing up the low K feeding concept. Back in the day if you were feeding MSU at 100ppm N you were feeding 110 ppm of K.

If you are feeding a 7-9-5 at 30 ppm N you are now only feeding 21 ppm K. Thats still more than the 3-5 ppm from K lite at comparable N strength, and higher than any environmental litterature value I've come across, but that's a much narrower gap than the good old days.