Mess 3

Micro Environment Subsistence System (M.E.S.S.)

Hydroponics
In repeated texts hydroponics is reported to be cheaper and more efficient than soil gardening. It provides a means to provide optimum root conditions and avoid soil pathogens. Without root resources limits plants can grow to their optimum given heat, light, and CO2 limits. Hydroponics via aquaculture is the simplest to set up. The author has not done experiments in hydroponics to determine if it requires less or more water than a soil-based garden. In general there must be some means to support the roots. In general the solution must be pumped to/from the plants and the source of the nutrients, whether the fish tank, the black water tank, or ???? Typically there must be some medium for the roots to adhere to that holds enough moisture between nutrient floodings. Mediums that may work for you are gravel, smooth river rock, sand, marbles, etc., looking for something that holds moisture on its surface, while providing adequate air-space for the roots.

Check your library for books with further details on physical materials and layout.

As mentioned elsewhere regarding worm castings, to extract the nutrients from a compost for use in a nutrient solution think of a tea bag. Fill a sack with compost and put it in warm water for about a week, put your compost in a watertight can, etc. The nutrients seep out into the water. Filter (i.e. thru more soil, sand, etc.) to leave the solids behind for use elsewhere. NOTE: Many trace elements essential for plants may not dissolve in the water from natural sources. The needs to obtain and “insert” these elements in a more artificial “chelated” form is an inherent “problem” of hydroponics, vs soil where natural organisms handle all the balancing.

Construction
Think in terms of a "rooftop garden", which then of course can be located on virtually any surface exposed to sunlight. A lightweight, controlled environment where the growing conditions for plants are optimized.

For your growing area, envision you use planting beds 4' x 8', with 16” wide paths all around for ease of access. Using this method, for every 32 ft. sq. planted, your garden will cover about 5' x 10', therefore 1,000 ft. sq. of planting area would require nearly 1,600 ft. sq. of surface. Framing the area allows extra topsoil or compost to be added in to create a thicker growing area, raises the growing surface above night chilled air, and reduces the need to bend. Consider each 4' x 8' bed as a large self-watering planter.

Water-tight base membrane
Maintain some absolute minimum bottom moisture, avoiding enough to "drown" roots, with excess draining to storage / reprocessing. Maintain a reservoir by such method as you can to keep this bottom moisture in place. A small number of W/N roots can exist in the water, but depth should be no further than 15 cm due to the limited amount of dissolved oxygen. When the water level drops in a plants growing medium where roots are growing in the water, these water tolerant roots change into O roots, a process taking only 2-4 days. However, this is not reversible. If water returns to the original depth such that the changed roots are now flooded, the plants wilt within a few hours and do not recover. You need to create a medium with such large air spaces that no matter how much water is around, the roots will still find plenty of air, but dense enough that water can move up by capillary action and keep the medium moist.

Wick material
A durable, non-toxic, non-rotting material capable of wicking water up, 2" to 3" thick, which also serves as an air-gap.

Expanded volcanic rock, Perlite (Danger to worms), it's principal value is aeration, as it does not hold water & nutrients as well as vermiculite. It has a pH of 7.0 to 7.5. It can cause fluoride burn on the tips of some foliage plants.

Vermiculate is expanded mica. (Danger to worms) It will hold large quantities of air, water, and nutrients, with a pH of 6.5 to 7.2. It comes in four particle sizes, use larger sizes, at least 2 or 3. Fiberglass w/rock. (Danger to worms)

Filter screen / mat
For high-tech fiberglass screen or woven mat. Low tech sticks, twigs, stems (needs to be monitored/replaced). This holds growing medium above wick/air gap.

Enclosure
Whether vapor-tight canvas, adobe, stainless steel, or concrete, walls are necessary to exclude hungry critters, and avoid drying or damaging winds. A typical greenhouse has transparent walls to allow in more light. Is the engineering challenge and expense of walls of glass worth it, or even warranted? Consider you put into an otherwise open field your 1,000 sq. ft. garden. Your plants have access to all of the direct and indirect light from all angles that might fall on that 1,000 sq. ft.

Put an eight foot high solid opaque wall around your garden, and you plants are in shade at the bottom of a well. Line your wall though with highly reflective material and you plants are essentially back to receiving all of the light that would otherwise fall on their footprint. Place at the top of the structure a light selective surface (discussed earlier) and you could if desired have a virtually air-tight structure.

Typical soil
Soil is the loose mineral and organic material which provides nutrients, moisture, and anchorage for land plants. The mineral aspect starts as rock, which is physically broken in to smaller particles by mechanical weathering, wind, water, freeze/thaw, and life once it is established. Particles size ranges are:

Sand   -    0.05 to 2.00 mm Silt      -    0.002 to 0.05 mm Clay    -    < 0.002 mm

Cation exchange capacity
The smaller the particles, the greater the surface area for any given mass. Clay size particles have so much additional surface area that the permanent negative electrical charge of the surface electrons becomes a significant consideration, and they readily attach to molecules other than the parent rock. This electrical charge difference is referred to as the Cation Exchange Capacity (CAC). The higher the CAC, the more easily these particles make nutrients available to roots and soil life, including water. Zeolite means the stone that boils. I've read that a zeolite crystal the size of a pinhead, when devoid of water, will have an internal surface area equivalent to a bedspread. This porous structure provides significant cation exchange capacities when added to the growing medium.

CEC of Soil Textures, showing the relative amount of nutrients the soil can hold in a useful manner.

Sand                    3 to 5 Sandy loam       10 to 20 Loam                 15 to 20 Silt loam            15 to 25 Clay loam          20 to 50 Organic soil       50 to 100

Soil organic matter (90% carbohydrate), as it decomposes, makes the nutrients available to the crops. It increases water holding capacity, aeration, and buffers soil pH.

Soil PH
Soil pH is a chemical term "potential of Hydrogen" which is a measure of acidity (lower) or alkalinity (higher) of a solution or substance, numerically a reading of 7 is a neutral solution. As you move in either direction away from 7, the scale is logarithmic, that is a pH reading of 8.5 is ten times more alkaline than a reading of 7.5.

Any atom with a number of electrons that do not "match" the protons in the nucleus is an "ion". The "pH" of a solution is a count of the number of ions. In a glass of water there is generally one hydrogen ion in every 10 million water molecules. The pH of water is set at 7 (7 zeros in the count). Stomach acid has one hydrogen ion for every one hundred molecules, or a pH of about 2. (two zeros) The ions work to tear apart the molecules of food.

Soil pH depends of course on the elemental and molecular composition of the basic soil. Most of Arizona for example contains high amounts of the mineral calcium carbonate (free lime), which keeps the soil pH at around 7.5 to 8. Nearly all ofthe carclim carbonate would have to be neutralized with a strong acid to begin to drop the pH appreciably. Remember, 98% of plant nutrition absorption is from minerals dissolved in soil water. The effect of soil pH varies with the mineral, presence of other minerals, and soil type. In alkaline conditions micronutrients such as iron, zinc, copper and manganese become chemically bound and may precipitate out of solution. In acid conditions calcium, phosphorous and magnesium may become chemically bound and precipitate, while manganese and aluminum can dissolve to toxic levels.

Soil water retention
Of water applied to a soil of primarily one size of particles, the water held will generally be around: Fine sand       -     2.0% Sandy loam   -     8.5 % Silt loam        -   10.9% Clay              -    13.5% Soil physically typically consists of:

45%      -  Mineral material (sand, silt, clay) 1 - 5%   -  Organic matter (plant & animal remains) 2 - 3%   -  Micro-ogranisms 25%      -  Soil atmosphere 25%      -  Soil moisture

Water conservation
Exchange of water molecules into the air occurs only if there is a vapor pressure difference between the evaporating surface and the air, i.e. evaporation is nil when the relative humidity of the air is 100%. A change of state from liquid to vapor, and therefore necessitates a source of latent heat. To evaporate 1 gram of water requires 540 calorie of heat at 100 degree Celsius and 600 calorie at 0 degree Celsius.

Evaporation rate is affected by wind speed, 1 mm of the water surface the upward movement of vapor is by individual molecules -- "molecular diffusion", but above this surface boundary layer turbulent air motion -- "eddy diffusion" is responsible.

It is reported that even three or four stones around a tree in the desert make a difference between survival and non-survival. If you put a pile of stones in the desert, it is often moist below them.

Salinity depresses the evaporation rate. Sea water has 2-3% less evaporation rate than fresh water.

Evapotranspiration is a combination of evaporation from the free water surface such as oceans, lakes, rivers, streams, and ponds; and transpiration from plants, vegetation, soil and grounds.

Transpiration -- water loss from plants takes place when the vapor pressure in the air is less than that in the leaf cells. 95% of the daily water loss occurs during the daytime, water vapors transpired through small pores, or "stomato", in the leaves, which open in response to stimulation by light. The internal (stomatol) resistance of a single leaf to diffusion is an important control on transpiration, and it is dependant on the size and distribution of the stomato. External resistance of the air to molecular diffusion arises through frictional drag of air over the leaf (larger leaves have lower transpiration rates) and the interference between diffusing molecules of water vapor.

What factors control the net loss of water (or net evaporation) in the atmosphere:

Temperature: increase the temperature, increase the activity of water molecules and loss the water molecules, therefore, affect the net rate of evaporation. Temperature of the water, and the temperature of the evaporating surface. It takes great amount of input energy to change from liquid to gas. Temperature (evaporation) is a function of latitude, season, time of day, and cloudiness.

Relative humidity of the air: hot air can hold great deal more water vapor than cold air. Measure the water vapor content in the atmosphere expressed in percentage. What % of the water vapor has been saturated in the air. The higher the relative humidity, the slower the evaporation rate. Sometimes, this refers to the vapor pressure deficit - which is the difference in vapor pressure between the water surface and the atmosphere.

Wind velocity: The higher the wind velocity, the more the mix of the air, and the better the chance for evaporation rate. Stability of the air or the stillness of the air is also affect evaporation rate.

Above all, the temperature of surface is the most important factor affecting evaporation. The warm surface area gets largest evaporation. Arctic and Antarctic, or mid-latitude in the winter, evaporation gets very low. Sea has open water surface, tropical and subtropical areas, evaporation is high.

Availability of moisture:  The moisture supply in the soil is limited, plants have difficulty in extracting water, and AE rate falls short of PE (Potential Evaporation) which is the moisture transfer from a vegetated surface is referred to as PE, and when the moisture supply in the soil is unlimited. The evaporation equivalent of the available net radiation.

To contemplate a perhaps complex approach to preserving your garden water, enclose the garden in essentially a water vapor tight structure. (For starters, think greenhouse.)

Although greenhouse glazing often gets credit-blame for interior heating by preventing radiation of the infrared from the heated greenhouse contents, tests show that even when the glazing is made of materials transparent to infrared, the greenhouse still warms. Even in greenhouses with infrared blocking glazing, night sky radiation still cools.

It appears that the glazing, whatever the material, provides a great deal more toward warming merely by preventing convection currents than does blocking ground level infrared radiation.

If the larger factor is convection currents and physical transfer of heat, then in areas such as the author's, where the purpose is avoiding water loss to open air flow, look to gmize entry of un-desired light frequency, and avoid within the greenouse dark colored heavy mass objects, that would create a miniature "heat island" within the greenhouse.

Use night-sky radiation to cool a thermal storage area, perhaps a large container of phase-change material. Use the atmospheric condensers discussed in the Appropriate Technology appendix to dry garden air, then re-heat it before exhausting it.

Optimized growing medium
A shallow bed of compost, worm castings, etc. 3" to 6". If you are taking a rooftop approach, weight can be critical. Weight estimates from ECHO  for a 4' x 8' bed are:

DEPTH    WEIGHT COMPOST        WEIGHT SOIL 3"                 598 lb.                                          947 lb. 8"               1,595 lb. 2,552 lb.

ECHO tells us a garden can be planted in fresh organic material if one does not have compost, grass clippings, food scraps, etc. as an example. Whenever possible, cover new such beds with an inch or more of compost before planting. So far compost appears to be the ideal medium. Transplanting holes may be filled with manure, and consider watering with manure tea. Transplanting from sprouting trays helps keep growing medium "in use".

Shallow rooftop type beds may require annual reworking, or after each crop, as the depth of the bed drops as the material turns to compost, but the trade-off is the quality of the medium, which is essentially pure compost, a near "ideal" medium. To rework the bed, temporarily remove the compost and put the new organic material in the empty bed, then put the compost remains back on top.

There is an element of artistry involved in creating a medium that hold sufficient air and water. In my containers I've been using a column of perile surrounded by the compost, with the perlite extending to the water mat, but the compost held away by rocks and a fiberglass mat. A key in all being at least 3 inches of soil above the water level.

Whether commercial mats of capillary material, fiberglass or other non-biological materials, or biodegradable items, the purpose is to provide a means of wicking water in a bed.

Compost tea, worm casting tea, even the runoff from water thru (first solar pasterurized) humanure can serve as an organic "hydroponic" solution. One approach involves  is construction of a "wall" from cut and stacked tires, filled with inert material such as gravel. The professor's article is written around graywater, but I see no physical impediment to use of these other solutions.

In a "solid" growing medium, plant roots may only make contact with 1/10% to 3/10% of the particles in the soil. (Still, with our present open-loop system, how many crops does it take for most of the nutrients to be taken away?)

Rooting depth
Your particular crop selection obviously effects the details of your food production facility. In open field conditions, plant feeder root depths will typically be: Alfalfa	3 to 6 feet Beans	2 feet Beets	2 to 3 feet Berries (cane)	3 feet Cabbage	1-1/2 to 3 feet Carrots	1 1/2" to 2 feet Corn	2 1/2 feet Cotton	4 feet Cucumbers	1-1/2 feet Grain	2 to 2-1/2 feet Grain, SOrghum	2-1/2 feet Grapes	3 to 6 feet Lettuce	1 foot Melons	3-1/2 to 3 feet Nuts	3 to 6 feet Onions	1-1/2 feet Orchard	3 to 5 feet Pasture (Grass)	1-1/2 feet Pasture (w/clover)	2 feet Peanuts	2 feet Peas	2-1/2 feet Potatoes	2 feet Soybeans	2 feet Strawberries	1 to 1-1/2 feet Sweet Potatoes	3 feet Tobacco	2-1/2 feet Tomatoes	3 to 4 feet