Effect of N on P. armeniacum

[naoki]

I happened to see this fairly recent paper:

Mou Zong-min, Yan Ning, Li Shu-yun and Hu Hong, 2012. Nitrogen Requirements for Vegetative Growth, Flowering, Seed Production, and Ramet Growth of Paphiopedilum armeniacum (Orchid). HortScience May 2012 vol. 47(5): 585-588


Only abstract is available (but PM me if you want to take a look).

Well, there aren't so many nutrition studies which use our favorite group of orchids, so I thought that some of you might be interested in. I describe a summary of interesting aspects.

Culture:
- Sphagnum moss in 4" pot.
- 24/18C
- Fertilizer: Hogland and Arnon (1950), 50ml/pot, once a month.
- water as needed

Treatment:
- Nitrogen: 0, 105, 210, 420 mg/L (=ppm) (I'm not sure NO3 or NH4).
- Started in Nov, and ends in Aug next year (short-term experiment)
- sample size: total of 360x 3 year old seedlings to study vegetative growth, and 200x 5 year old flowering plants to study sexual and clonal reproduction.

Results:
1. Effects on sexual reproduction:
- The flower lasts longer with low N (28 days with 0N vs 21 days with 420ppmN)
- petal diameter is largest with 210ppmN
- 210ppmN plants produced largest fruits, and the germination rate of the seeds were much higher (22% vs 2-3% for the other ppm)
- The quality of seeds under higher N is much better. In other words, the seedlings derived from seeds produced by higher N moms grow better in flask (measurement taken for 6-month old seedlings in the flask). Dry weight of a 6-mo seedling: 6.53, 7.21, 13.12, 23.32mg (from 0N to 420ppmN). I'm really surprised to see such a big difference.

2. Effects on vegetative clonal reproduction:
- The mom under 105ppmN produced the largest new growth (58% larger than 420ppmN).

3. Effects on growth of seedlings:
- under low N, more lower leaves die, and slightly more new leaves are produced (only the highest N produced significantly less leaves), so high leaf turn over rate.
- But overall increase in leaf area is higher with more N
- higher N and chlorophyll concentration in 210&420ppm


Well, high N is usually associated with more vegetative growth at least for the short-term (this is shown many times in orchids). So that part wasn't so interesting. But I thought that it is very cool to see the dramatic effects of N on reproduction. High N plants make better kids by sexual reproduction, but low N plants appear to shift the resource toward asexual reproduction. Orchid seeds are tiny, and they don't appear to put much resources (no endosperms). But the nutrient status of the parent has dramatic influence on the quality of kids.


Since their culture is quite different from how most of us grow paphs (in the US), the absolute N concentration is not directly applicable for us.

 

[PaphMadMan]

210ppm N is a standard concentration for Hoagland and Aaron (1950), mostly in nitrate form, 6:1 ratio with N from ammonium I think. I can only assume that the experimental treatments would maintain that ratio in a well designed experiment, and that all other concentrations would be held constant. Hoagland is standard complete hydroponic formulation in scientific studies, with potassium and calcium in similar ppm with the 210ppm nitrogen.

Interesting experiment, but very short term, and not sure how applicable it is for typical Paph culture as you said.

 

[Justin]

interesting. getting the popcorn ready to watch this one...

 

[Brabantia]

Is it informations about the frequency of fertilyser distribution? With a such high concentration in salts I assume that the substrate never dry!?

 

[Rick]

Despite the relatively high concentration of salts, the authors apply very little per application.

They add only 50 ml of solution to 785ml pots of moss once per month.

So in water saturated moss the effective concentration if using the 210ppm solution dilutes to only 13.3ppm N at dosing (which I presume decays through time by both plant uptake and bacterial action).

Another way to look at it is they are adding (50/1000) X concentration X12 applications per year/pot

So for the 210ppm concentration dosing it only comes to 126 mg/N per pot per year.

Most growers probably fertigate to pot saturation 2-4X per month, but even at 100ppm N (the traditional dose concentration) this would be orders of magnitude greater than the optimal dose in this experiment.

 

[naoki]

Kirk, I'm not sure how they changed the N concentration without changing the other elements. The easiest way seems to be to change the amount of ammonium nitrates. But then NH4:NO3 ratio changes.

Brabantia, fertilizer is once per month as Rick pointed out, but they don't mention frequency of watering (they watered "as required").

Rick, as we talked over email, I agree it's not easy to get the absolute amount of N available to plants. I wasn't going to stretch the results to guess what would be optimal N for continuous feeding. But you made me curious about the rough comparison, so I measured the amount of water which is kept in bark based media.

1. I measured the weight of a dry pot (with Paphs).
2. I water the dry pot in the way I usually water.
3. After a couple minutes, I measured the pot again.

I did this to 5 pots (2.25" Rose pot with the height of 3.25").
The media is about 1 year old, fine bark:coarse Perlite:cheap sphag=3:2:1.

Dry(g)	WH(g)	WH/Dry 
62.484	17.729	0.284
45.448	12.306	0.271
50.762	12.350	0.243
55.159	10.443	0.189
58.091	12.992	0.224

WH: water holding (g) = Dry Pot weight - Wet Pot weight. This is not a correct way to get the water holding capacity, porosity etc. But it's good enough.
WH/Dry: 1st column / 2nd column.

So in my case, each watering is giving about 13.164 g (95%CI = +- 2.39g) of water on average.

I water 2x a week, so I water 52 weeks x 2 = 104 times a year.

So to get mg of N per year per pot, we can use:

104 x 13.164 g x (ppm) / 1000

With 30ppm for every watering, this is 41mg of N per year (we are aware of problems with this type of simplistic calculation).

But with their watering, the available amount of N is probably much lower than 126mg of N. Fair amount of N will be washed out at the 1st watering after fertilization (even if sphag can retain fertilizer much better than bark). So I agree with Rick, that 210 ppm isn't that high.

 

[Brabantia]

Thank Rick and Naoki for this excellent discussion and exchange of informations.
I am curious to know how long remains a concentration of let us say 30 ppm N in a pot. Because there is always a competitions between what is taken by roots and what is consumed by the microbial flora and the substrate. It seems to me that a inert substrate (mineral) should allow to keep for a longer time at the disposal of roots the elements supplied by fertilizers??
I have also the impression that the roots mass also plays a big role. Example: two roots of 10 cms in a pot of 500 ml have less luck to get the same quantity of nitrogen that the same pot full of roots. This explains why some have plants which grow fast (important mass of roots) and others which have the same plant but who grow slowly. Achieve a good mass roots is the key of the success as far as the environmental conditions are performed.
We can continue the discussion about "on which factors can we play in order to increase the mass roots". ...substrate, hormones, phosphorus....light,temperature... but maybe this is an other thread.

 

[naoki]

I agree that lots of things influence the nutrients uptake. I look around primary literature about nutrients occasionally, but it is pretty complex, so I don't know the answer. Maybe, Mike, Ray or Rick has a better idea. My gut feeling is that most nutrients are washed out, so the media which can hold the water longest provide more available nutrients. So I would guess sphagnum moss is probably better than sand. But then, there is cation vs anion issue, too (e.g. sphag may retain cation more than anion).

But I think you are talking about how much N is taken away by cellulose eating bacteria (I think this is called N immobilization). I did find a couple papers about this topic, but I haven't read it thoroughly. I think Mike (Stone) mentioned that composting bark is one method to avoid/reduce this, and the paper did mention it. I learned that the issue is worse if the bark is contaminated with the "wood" part of the tree (xylem).

I agree that growing root seems to be the safer way to get robust plants. But we shouldn't forget that plants try to achieve optimum root:shoot ratio for a given environment. So lots of root with relatively small shoot might be good thing in one environment (e.g. nutrient, water limited) but it may not be the best in another environment (e.g. photosynthesis/light limited). Biology is complex, but it's fascinating!

 

[Rick]

I wouldn't underestimate the rate of microbial action. Its the basis of aquarium life support system design, and systems like the "wet/dry"process (which develops bacterial colonies on inert substrates like plastic balls) can take care of large amounts of N in very short time intervals.

 

[Rick]

But with their watering, the available amount of N is probably much lower than 126mg of N. Fair amount of N will be washed out at the 1st watering after fertilization (even if sphag can retain fertilizer much better than bark). So I agree with Rick, that 210 ppm isn't that high.

Correct that 210mg/L is not high if you only apply tiny amounts of solution at the time of application.

Remember that they only applied 50ml of fert solution to each 785ml pot of moss (they did not saturate the pot at watering to bring the pot media into equilibrium with the fertilizer matrix). So this automatically dilutes the fert concentration down to 5-6% of the original starting concentration in this case before even starting the conversation on washout and bacterial competition.

 

[Rick]

Thank Rick and Naoki for this excellent discussion and exchange of informations.
I am curious to know how long remains a concentration of let us say 30 ppm N in a pot. Because there is always a competitions between what is taken by roots and what is consumed by the microbial flora and the substrate. It seems to me that a inert substrate (mineral) should allow to keep for a longer time at the disposal of roots the elements supplied by fertilizers??
I have also the impression that the roots mass also plays a big role. Example: two roots of 10 cms in a pot of 500 ml have less luck to get the same quantity of nitrogen that the same pot full of roots. This explains why some have plants which grow fast (important mass of roots) and others which have the same plant but who grow slowly. Achieve a good mass roots is the key of the success as far as the environmental conditions are performed.
We can continue the discussion about "on which factors can we play in order to increase the mass roots". ...substrate, hormones, phosphorus....light,temperature... but maybe this is an other thread.

yes

Alot of these experiments have been conducted with other plants and I suspect the results are not that different for orchids. If you search through the lit for hydroponic growing you can probably get the equations.

Hydroponic (constant application systems) have been demonstrating very efficient results because losses to washout and bacterial competition can be eliminated. Some of the coupling of fish/shrimp farms with crop plants demonstrate that water quality applicable to fish culture (very low N concentrations) is excellent for growing plants hydroponically.

 

[Rick]

I see a lot of interesting directions in this paper with regard to pot sizing, media selection and watering/feeding strategy.

Note that single armenicum plants are placed in 4" pots of sphagnum moss. I think most of us would consider this an "overpotted system in a very water retentive media", and generally pot our small species much tighter in less water retentive media (Just like Naoki's system).

Also this paper fed 1 X/month with a very limited amount of a fairly concentrated fertilizer (50mL, of a 210mg/L-N solution, per 785 mL moss media) while Naoki is feeding a 30mg/L-N solution to saturation, 4X/month into 275 ml of media that only seems to hold about 5% of the water poured into it at any given time.

Now this exercise is only for N which has much greater utilization for plants and bacteria

But I can see trends of "common orchid culture practices" that all tend to reduce NPK loads for better results by:

1) reducing pot volume to root mass ratios
2) decreasing water retention in media.

Ultimately we shift to baskets of rock and mounted systems that retain almost nothing, and increase the watering frequency with very dilute NPK solutions.

 

[Rick]

while Naoki is feeding a 30mg/L-N solution to saturation, 4X/month into 275 ml of media that only seems to hold about 5% of the water poured into it at any given time.

This assumes that Naoki's rose pots are filled to the top with media and roots.

 

[Rick]

I was just doing some math that might be usable as a monthly N application pot target.

For the paper experiment "optimal" comes out to 0.013 mgN per ml of pot volume per month.

Naoki's system (based on his water retention values) comes out to 0.011mgN per ml of pot volume per month. (almost the same)