Soil DOE - Beating a dead horse!

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macdad

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I love beating a dead horse, so I decided to perform a 3 Factor DOE on soil components.

First off, a the reasoning... I am having a difficult time finding certain soil components like pumice, smaller lava stone, haydite etc. I have called and searched like crazy :) I also have a difficult time driving a long way (several hours) just for soil. I wouldn't mind if I could also view/buy trees, but that is another story.
Secondly, I can't afford Akadama. I have also read that things like hard fired clay, Akadama and the like do not survive the freeze/thaw cycles. It is simply something that I don't want to worry about (the OCD in me will drive me crazy)!

So, I have 6 soil components, 2 for each category.

Grit





Porous



This is Zeolite. Supposedly very absorbent, but the grain size is small.



Found a local supplier of grow stone. Saves on shipping!

Organic



Just something that I picked up at Lowes



Purchased at Home Depot

More to come on the experiment setup and results... Wife needs the computer :(
 
She didn't need it ;)

So another reason for this DOE. Smoke made a comment on another forum (I think it was a different forum) about an experiment that someone conducted. They gave the amount of water held by various materials. Smoke said something along the line of, "I am more concerned about how long it retains the water." That is paraphrased.

Disclaimer, I am an engineer with Six Sigma Certification. I am not a statistician. There are plenty of holes that can be poked in this experiment, all of which are open to discussion. Technically, I should have started the testing with far more factors, perhaps performing a fractional factorial. However, I have limited time and far more limited resources.

The only active manipulated factors in this experiment were the soil components above. If I had more time, I would also add container shape (different evaporation rates), Heat/no heat added, air movement, etc. The list would be long, but I just didn't have the supplies to set up 16-32 samples.

OK, enough of the disclaimers, on to the test and results.
 
With, 3 factors, each with 2 level settings, that is 8 different treatments (2^3 = 3). This is a full factorial. The container is Blue Solo Cups (I think they are 18 oz.) with 4 drain holes drilled in the bottom.



Not perfect, but it worked.

My daughter helped by labeling some tooth picks.



And I had another "helper"



I chose to mix 30% of each soil component for each treatment/combination. Although this would not be the normal proportions, I didn't want mix percentages to be a factor. I wanted to see if the components, in equal measure, would stand out statistically.
 
I mixed up all the combinations and weighed them dry (and recorded the weight).

I then poured one full Solo Cup of water through each treatment. I gave each one an arbitrary drainage rating from 1-10. Then, I weighed them to determine how much water was retained on the initial watering. Next, I soaked them in a tub full of water for 2 hours in an attempt to fully saturate them. I pulled them from the tub and allowed to drain for 30 minutes and weighed again. Below is a chart of each treatment comparing initial watering with the prolonged soak weight:



The data is in grams of water. Notice there is very little difference between the initial watering and the soak for every combination. If you look at the data point for Sand/Growstone/Compost treatment, the retention is very high on the initial watering. I believe that I didn't allow all the water to drain out before I weighed it, therefore skewing my results a bit.

A few other points on this chart:

  1. Grani-Grit holds less water than sand (due to particle size)
  2. Growstone holds less water than Sweet PDZ
  3. Compost and Pine Bark are a mixed bag regarding water retention
 
Here is a little data showing the analysis of significant factors regarding water retention:



Notice both grit and porous factors are significant with regards to water retention. No real surprise there.

Oh, I also forgot to mention. I didn't sift anything, because I am LAZY. I also wanted to make the level settings of my factors significant enough to overcome the many noises in this experiment.
 
Next, I went about my business and weighed the cups every 12 hours give or take. Unfortunately, it has been quite humid and the daytime temperatures in the low to mid 70's. One if the observations is that the samples lost little to no water through the night. I don't think this would be a surprise to many either. Although, I do believe the results would be different over the hot summer months when the temp stays in the 70-80s through the night.

On to water retention. I thought about this a bit on how to compare it, but finally landed on simply averaging the total water loss over 5 days. See below:



There are a few things to gather from the chart.

  1. On average, growstone lost less water day over day compared to Sweet PDZ
  2. There was a significant difference between Compost and Pine bark when combined with Growstone. Theory: Compost was hindering the water retentive properties of the growstone.
  3. There was very little difference in water loss between Grani-Grit and sand with respect to Sweet PDZ. In fact, the treatments with Sweet PDZ all lost close to 14 grams of water per day.

I find fact number 3 quite interesting. There could be a lot of reasons for this. I may pursue this further, however, I am not sure that I want to use this as a main component of my soil.
 
Last edited:
One more chart to show is my arbitrary drainage ratings:



Since there was no scientific method to this measurement, you can take it with a grain of salt. Bottom line, larger grit drains faster than smaller grit. Not earth shattering. This feeds to the final decision on components, though.
 
Conclusions and Questions

With regards to daily water loss, the Growstone/Grani-grit/pine bark combination is the winner.

Due to the poor drainage, unsifted sand is out of the picture.

Although Sweet PDZ does not retain water over the long run as well as growstone, it retains a higher volume of water. Perhaps an experiment with Growstone/Grani-grit/Pine Bark and a handful of Sweet PDZ is warranted.

I believe I also want to test this combination in a cup and a bonsai pot. I don't know how it will hold up with more surface area to lose moisture from. I may also attempt to add heat with a light of some kind to determine how it will fair in the summer months. I cannot have a mix that will dry out in a matter of hours.

Question: Does anyone have a way to estimate the amount of water uptake from a tree? Does that calculation exist? While Growstone seems to retain water well, it doesn't retain a lot of it...
 
So which tree type did you do the test on?
What age was the tree, saplings?

You could just try a simple mix of the stone [ any just purely silica ?] and some compost.
Say by volume, 90 to 80 % inorganic and the rest as compost.

But are you testing for trees at the developing branchlet stage and in say pre-bonsai pots?

The idea here is you may be able to get away with a simple mix of just inorganic and organic.

Down here we can use builder's gravel [ silica ] at 5mm with compost.

Experience has shown that it does not matter the particle size of the compost [ we use 2 to 1 mm or smaller - remember decay is more rapid down here ] and when re-potting, have observed that the compost goes back to irregular spheres at around 3 to 5mm.

So perhaps you just need to grab a few say - hackberrys - as saplings and just grow them for a year see what happens.
Good Day
Anthony

Can you lay down some straw or other for the freezing factor outdoors ?
 
I remember Kathy Shaner talking about similar experiments done for soil drain layers using different grits (coarse to fine going up) and basically said that the test is okay but nowhere near real life since it was done without the tree using moisture which will basically throw all the results out.

Your experiment shows one facet for consideration...maybe a good starting point for each locale but should be used only as such.

Tree water uptake depends on; type of tree, health of roots, volume of leaves, wind, heat, humidity, sun exposure, temperature, etc. etc.
 
Anthony said:
So which tree type did you do the test on?
What age was the tree, saplings?

You could just try a simple mix of the stone [ any just purely silica ?] and some compost.
Say by volume, 90 to 80 % inorganic and the rest as compost.

But are you testing for trees at the developing branchlet stage and in say pre-bonsai pots?

The idea here is you may be able to get away with a simple mix of just inorganic and organic.

Down here we can use builder's gravel [ silica ] at 5mm with compost.

Experience has shown that it does not matter the particle size of the compost [ we use 2 to 1 mm or smaller - remember decay is more rapid down here ] and when re-potting, have observed that the compost goes back to irregular spheres at around 3 to 5mm.

So perhaps you just need to grab a few say - hackberrys - as saplings and just grow them for a year see what happens.
Good Day
Anthony

Can you lay down some straw or other for the freezing factor outdoors ?
Click to expand...

That would be a good test. If I were to predict the future, I think I will start using this combination is a slightly different proportion of a few cheap trees. Then, as time progresses with observation and experience, it will surely morph into something else. Thank you for your input. I have not determined what stage of the trees development that this would be used for.

Also, I am not sure regarding weather the straw will help with the freeze/thaw cycles.
 
Poink88 said:
I remember Kathy Shaner talking about similar experiments done for soil drain layers using different grits (coarse to fine going up) and basically said that the test is okay but nowhere near real life since it was done without the tree using moisture which will basically throw all the results out.

Your experiment shows one facet for consideration...maybe a good starting point for each locale but should be used only as such.

Tree water uptake depends on; type of tree, health of roots, volume of leaves, wind, heat, humidity, sun exposure, temperature, etc. etc.
Click to expand...


Agreed on all points. That is another reason I didn't want to get too involved with the experiment.

Regarding the water uptake of trees, that is exactly why I did this experiment without trees. The trees would introduce way to many variables that I cannot measure. Ultimately, it would probably be good to test with trees to determine a mix that is robust to these factors, but I am LAZY. That experiment probably won't happen. Also, I could plant 8 saplings of the same age and relative size, and I would bet they would each use water differently.
 
It also depends on your watering schedule and how. The tree's stage (i.e. in training vs maintenance of a "real" bonsai).

I am leaning on using richer more organic mix for my trees while in training...then slowly dial the organics down as the trees "mature" to bonsai. This is my plan for now at least. :)

Good thread. :)
 
Hi Macdad

Your floor looks a lot like mine, it must be a girl thing:)

There is something you need to look at with your experiments.

The materials you have used have a high level of microporosity that will take up water and which may not be available to your plants. Your testing has not taken that into account. While water holding ability is important, what is more important initially is Air Filled Porosity, which is how much air is present in the soil after draining. This factor is what keeps plants alive in wet weather and with frequent watering. AFP varies with soil particle size and depth of pot. Generally your are looking for a range of 15-25% AFP for healthy plant growth.

What you are looking for is Available Water, which is measured by planting something in the soil, letting it settled for a few weeks, then measuring the weight of the pot and plant after watering, and then wait till the plant wilts and weigh again, this will tell you how much available water the soil holds. This will vary with plant type and sol AFP.

Paul
 
63pmp said:
Hi Macdad

Your floor looks a lot like mine, it must be a girl thing:)

There is something you need to look at with your experiments.

The materials you have used have a high level of microporosity that will take up water and which may not be available to your plants. Your testing has not taken that into account. While water holding ability is important, what is more important initially is Air Filled Porosity, which is how much air is present in the soil after draining. This factor is what keeps plants alive in wet weather and with frequent watering. AFP varies with soil particle size and depth of pot. Generally your are looking for a range of 15-25% AFP for healthy plant growth.

What you are looking for is Available Water, which is measured by planting something in the soil, letting it settled for a few weeks, then measuring the weight of the pot and plant after watering, and then wait till the plant wilts and weigh again, this will tell you how much available water the soil holds. This will vary with plant type and sol AFP.

Paul
Click to expand...



Great post, Paul! That gets my engineering brain thinking... I will have to mull this over for a while. Ultimately, the challenge is to have bothe water and air available in the appropriate quantities. Obviously, I am looking for a soil like everyone else. Something that is both free flowing and water retentive.

I will have to run this wilt test. Do you know anyone else that has performed this test with their own soil mix?

Another question regarding micro porosity. If I recall from high school chemistry, water is more adhesive than cohesive. Do you know if this will aid in pulling water out of the porous material? For instance, if the roots are in direct contact with this material, will the water wick out??

I definitely think the floor thing is a girl thing. I have three :)
 
Anyone, want to comment on this?

K is testing the ball bearing idea, he planted a tamarind in a mix made of a bag of marbles and compost. Our compost is 1 to 2 mm in size. The marbles are those bags of pitching marbles sold by the 100, from China.

Please note, there is no problem with the soil mix being used since 1980, but K has always had a curious mind, and will [ very ] often do this.
Seems to increase when he is painting, he has three very large commissions to do over the next three years. Imagine the mischief - chuckle.
Good Day.
Anthony

* He also has trees growing in a local stone, at around 4 to 5 mm, plus compost, and hydroponic balls plus compost, as well as the acrylic coated river stone sold as aquarium decoration.
 
Honest I have used Play Marbles, Aquarium gravel, Deco art stone, and many more items to long to list. All seem to work ok as long as they get water and nutrients. I am almost done making everything the same though as it is easier to keep track of. For me it is Dry Stall(pumice) 2/3 and Traction grit 1/3 for all. In Spring some of the new additions will get the same with some Pine Horse Bedding like Wisteria, Willows, Abriels, and Burning Bush. They have a different Nitrogen need as well as Bougies. Prior to that everything else will get the same and those new additions will be in a different water and fertilizer zone bit all the same as well.

Grimmy
 
Interesting thread. I am especially pleased by the effort to collect data and analyze it instead of relying on anecdotes. Thanks!!

It is well known that tree roots need to have at least a 12% pore space in addition to some free water.

I would measure this by carefully measuring volumes and not weights. I would place a carefully measured volume of the experimental mix into the cups before watering (keeping this volume at some consistent amount less than a full cup). I would measure an amount of water, just less than a full Dixie cup, with a kitchen measuring cup (a graduated cylinder would be better if you have one). Then I would nest a perforated cup inside a another cup with no holes, pour in the known amount of water (which should 'drown' the mix), and then lift up the perforated cup of mix, letting all the water drip into the unperforated cup. After water quits flowing from the perforated cup, I would measure the amount of water in the unperforated cup. Clearly the missing water (water poured in minus water volume recovered) is in the mix.

fractional pore space filled = water volume 'lost' / mix volume

I think this is a better response metric than weight (though I suppose it could be problematic with organics that 'puff up' when wetted)


BTW, since you are an engineer, you might want to read this paper on soil water potential and maybe some others before you decide what to do next.
 
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