Water movement in soil is called Hydrology.  It's important to design a soil bed for a Biosphere where water is delivered to all the plants and not drained away.

After taking apart the last Biosphere version, I noticed fresh water is running directly from the dehumidifiers down to the marine layer.  Most of the soil is dry as a bone.  There are a few plants that can stretch their roots to the column of water that survived.  

This version needs to have the soil bed engineered for water flow.  Part of the water cycle is rain; I've installed small dehumidifiers in the biospheres to take water moisture out of the air and give it to the soil; however, the dehumidifiers are point sources of water.  Without making an elaborate piece of equipment for irrigation, it may be easier to learn how Mother Nature does it and imitate it.

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Hydrology Goal

Before spending time on guessing how water moves around in soil, it's best to make a planting bed in the open air and engineer how the water moves.  

This is not new science and most of this knowledge is readily available through books and videos.  Below is a really boring video explaining how water moves through soil from a single point source.  Warning: The flick below is really boring and you may want to take it in small doses.  It was made in 1959.  All of the information on the video is stilled ignored today for lawns and general planting.

It's one thing to see a 1959 flick on soil moisture, but another to build it.  It needs to be determined, with the materials I have available, how I can keep water moving in all directions within the planting bed.  Larger clumps of soil act like a drainage path to the bottom of the tank.  The soil has to be chosen with enough organic material and air movement for plants to grow.  It's also possible to have tons of water, but plants cannot grow because they can't absorb nutrients they need.  

All materials have to be made of none plastic because of out gassing.  No plastics can be used at all.  In this test, glass is used as the container(s).

The mistake I did on the last biosphere is not requiring water to move sideways, but only down.  In this case, I want to save the water that drips from the dehumidifiers.  Below is a 5 liter beaker with sifted soil (10% to 20% organic material).  The particles are smaller than sand.  The bottom layer has 1 liter of sifter soil.

The next layer is sand.  Sand is isolated from the top surface will not take water until it is forced to by gravity.  The forces between water and sand is lower than water and find soil.  An 1 inch band of sand is layered over the sifted soil.  The rest of the beaker is filled with more sifted soil.

Last, two native California strawberries are planted to one side of the beaker.  And a Petri dish is put on the other side.  See below.

Close up picture of the dish.  The dish is put at an angle where the water from the dehumidifier will enter into the center of the beaker.  The water than balloons out in all directions (hopefully) in the soil.

Below is a picture with the dehumidifier on the dish.  The dehumidifier produces around 100 ml of water per 24 hours @ 25% RH and 21 C.  It depends a lot on the dew point of the day.  Sometimes it freezes up.  When the whole system is closed, a dehumidifier is used to take water from the marine layer and provide fresh water for land.  This devices takes the place of rain. Any run off goes back to the marine layer.   Since biospheres are really small, it cannot produce difference in air pressure and temperatures to force condensations at regular intervals.  

Water moves well (sideways) through tighter (smaller to a certain point) soil than looser soil.  (I don't mean compacted)This means the adhesion of water to clay and silt is very strong compared to pea stones, sand and mulch.  If sand is surrounded by small particles of clay/silt, it will take a "supper saturation" of the clay/silt for water to enter into the sand.  If sand has an opening to the surface, water will flush strait down through the sand.

It's also the same for mulch for your yard (or a duff layer in a forest).  Since the particles of soil are smaller than the mulch, water has the tendency to say in the soil and not venture up through the mulch.

When wetting compost with a watering hose, the top inch or so gets wet, but anything under stays dry because the adhesion of larger particles on top run off the water to the sides.  It's important to mix your compost pile while wetting it.  

 

Results

Water had to be put into the planter, before there was enough from the dehumidifier, because the plants may be compromised .  The dehumidifier makes about 100 ml of water every 24 hours. It tends to freeze up every 60 minutes; hence, holding water on the fins.  A wall timer is put into place to turn off every 30 minutes and on again.  It startes to make a steady flow of water after making that correction.  This is the same technique used in the BioSphere III.

300 ml of water is slowly dumped on the Petri dish.  It overflows and slowly is absorbed by the dry soil.  It starts to expand in the soil reaching the roots of the strawberries.  And it also shows on the side of the beaker.  No water ran to the bottom.

After running it for two or three days, no water runs directly through the soil to the bottom, but stays by the roots.  

Next Test(s)

Another beaker is filled up with the same sifted soil, but the layer of sand will have a section where sifted soil breaks through.  Since it has been observed that water climbs clay/silt faster than sand because of proximity of adhesion; when soil is dry and there is water in the sand, it will be wicked up into the rest of the bed.  The assumption is the dehumidifiers can only keep up with leaf transpiration.  It's also assumed this sifted soil will grow plants.  We are testing that assumption.