Overview of plant needs[edit | edit source]
The basic needs of plants are nutrients (certain atoms in certain forms), water, and light. On the scale of the Earth, our entire ecosystem is an essentially sealed environment.
Air[edit | edit source]
Plants need three primary gases from air.
Carbon Dioxide (CO2), which is used in their leaves in the photosynthesis process to combine hydrogen from water with carbon from CO2 to produce carbohydrates (sugars), with the oxygen being released. In normal seal level air, CO2 is at 350 parts per million (ppm), or .035%. Even this tiny amount is enough to support plant growth. Studies seem to show that the upper concentration limit for CO2 for plants is around 4%, which requires that all other growing conditions be optimized. But, plants cannot tolerate the 4% level unless there is sunlight present for photosynthesis. WARNING: In general, humans cannot breathe where the CO2 concentration approaches 3%.
Water will absorb it's own volume of CO2, and when evaporated will release the CO2. This seems nicely in tune with nighttime water condensation absorbing CO2, with daytime evaporation releasing the gas.
Oxygen for their roots. Roots can suffocate or drown without enough O2. Conversely, as aeroponics shows given access to nutrients and kept moist, roots and the plant will thrive when given lots of air. Aeroponics is cited as perhaps the most productive means of providing crops necessary nutrients. Aeroponics has plants suspended in holding material, in an air gap, which is kept in a spray of the liquid nutrient. The falling liquid also gains air which provides O2 for the roots in the liquid below. I continue experiments on a static means to approximate this. I've had modest success with containers set up with a bottom wick kept moist by an upturned bottle of water, several inches of perlite over the wick, then a tower of perlite up the center with compost around the tower. A WARNING: You may have heard that more houseplants are killed by overwatering than by underwatering." The problem with overwatering is not that the roots do not like to stay moist, but that if heavily watered, water fills most of the spaces ordinarily filled by air in dry soil. Plant roots require oxygen, but not all portions of a plant's roots require the same amount of oxygen. Plants can form what he calls oxygen (O) roots and water/nutrient (W/N) roots. Roots exposed to air specialize in taking up oxygen; those immersed in water specialize in taking up water and nutrients. When the water level drops in a plants growing medium, the W/N roots change into O roots, a process taking only 2-4 days. However, this is not reversible. If water returns to the original depth 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.
Nitrogen (79% of the air) to produce complex molecules. Most plants cannot absorb nitrogen directly from the air on their own, but must obtain it via their roots from a substance which embodies the gas atom.
The bulk of commercial nitrogen fertilizer is made using un-sustainable high energy chemical processes.
There are various methods to "fix" the gas into the soil, for example special bacteria, that can live in symbiosis with some plants:
Clover, alfalfa, select legumes, and select trees such as Neem and Russian Olive. Research what grows well in your area. It is the bacteria that make nitrogen available for absorption by plant roots. Fixing nitrogen takes energy. Every gram of nitrogen fixed requires 10 gram of glucose, with the plant feeding the bacteria growing on it's roots.
Blue-green algae can also absorb nitrogen and incorporate it into their cells, with the advantage it can be used as an animal (or human) food, or as fertilizer.
Lightning splits the N2 molecule, which can then combine with oxygen into a nitrogen oxide which can dissolve in rainwater, which was something that Tesla referenced in several of his papers.
In a free online pamphlet, Bill Mollison presents his "third world endless nitrogen fertilizer supply system." You will need a sand box, with a trickle-in system of water, and a couple of subsurface barriers to make the water dodge about. Fill the box with white sand and about a quarter ounce of titanium oxide (a common paint pigment). He indicates that in the presence of sunlight, titanium oxide catalyzes atmospheric nitrogen into ammonia, endlessly. You don't use up any sand or titanium oxide in this catalyic reaction. Ammonia is highly water soluble. You run this ammonia solution off and cork the system up again. You don't run it continuously, because you don't want an algae buildup in the sand. You just flush out the system with water. Water your garden with it. Endless nitrogen fertilizer. If you have a situation where you want to plant in sand dunes, use a pound or two of titanium oxide. You will quickly establish plants in the sand, because nitrogen is continually produced after a rain. This solution is carried down into the sand. If you are going to lay down a clover patch on a sand dune, this is how you do it.
Apart from the legumes and actinorhizal plants, there are a number of other systems involving nitrogen-fixing cyanobacteria, notably of the bacterial genera Azotobacter, Anabaena, and Nostoc. These systems involve the following:
- Gunnera-Nostoc. Probably all Gunnera species display a localised infection of the stem by Nostoc bacteria.
- Azolla-Anabaena. The aquatic plants of the Azolla family form a symbiosis with Anabaena bacteria.
- Liverwort-Nostoc. The liverwort genera Anthoceros, Blasia and Cavirularia all form associations with Nostoc bacteria.
- Lichen associations. About 7% of lichen species are not of the traditional fungi-algae symbiosis, but are instead formed of a fungi-cyanobacteria symbiosis. Nostoc in the bacteria genus is usually involved. The lichen genera Collema, Lobaria, Peltigera, Leptogium and Stereocaulon form this type of symbiosis. They are particularly important as nitrogen-sources in Arctic and desert ecosystems, where fixation rates may reach 10-20 Kg/ha/year.
- Leaf surfaces (the phyllosphere). There is increasing evidence that free-living N-fixing species of bacteria are abundant on wet and damp leaves in predominantly moist climates.
- Root zone (Rhizosphere). Free-living bacteria, for example Azotobacter species, may be more abundant in the areas immediately adjacent to plant roots and aid plant nitrogen nutrition.
- Free-living. N-fixing bacteria thrive where the Carbon:Nitrogen ratio is high and there is sufficient moisture, for example on rotting wood, in leaf litter, the lower parts of straw and chipping mulches etc.
Factores affecting nodule development
- Temperature. Depends on the bacteria species and the host plants, for example 4-6 deg C is adequate in Vicia faba, whereas 18 deg C or more is necessary for most sub-tropical and tropical species.
- Seasonality. For most species, fixation rates rise rapidly in Spring from zero, to a maximum by late spring/early summer which is sustained until late summer, then decline back down to zero by late autumn. In evergreen species, N-fixation occurs throughout the winter provided the soil temperatures do not fall too low.
- Soil pH. The legumes are generally less tolerant of soil acidity than actinorhizal plants. which is reflected by Rhizobium species being less acid-tolerant than Frankia species. Of the actinorhizal plants, Alders (Alnus spp) and Bayberries (Myrica spp) are most acid tolerant. Of Rhizobium species, acid-tolerance declines in the following order: cowpea group (most acid tolerant) - Soya bean group - Bean & Pea groups - Clover group - Alfalfa group (least acid tolerant). In poor soils which are low in Nitrogen, the introduction of N-fixing plants usually leads to considerable acidification (e.g., a fall in pH of up to 2.0 in 20 years for a solid stand), which itself will in time start to affect nodulation efficiency.
- Availability of Nitrogen in the soil. If Nitrogen is abundant and freely available, N-fixation is usually much reduced, sometimes to only 10% of the total which the N-fixing plants use. In trials with Alders, at low soil N levels (under 0.1% total soil nitrogen), the majority of N used by the alder comes from N fixed from the air; when total soil nitrogen is as high as 0.5%, only 20% of the N used came from fixed N from the air.
- Moisture stress. In droughts, bacterial numbers decline; they generally recover quickly, though, when moisture becomes available again. Some species (usually actinorhizal), for example Alnus glutinosa and Myrica gale, are adapted to perform well in waterlogged conditions.
- Light availability. Nitrogen fixation is powered via sunlight and thus will be reduced in shady conditions. For most N-fixing plants, which are shade sensitive, N-fixation rates decline in direct proportion to shading, i.e. 50% shading leads to 50% of the N-fixed. The relationship for N-fixing species which are not so shade-sensitive is not so clear: they may well continue to fix significant amounts of nitrogen in shade.
Water[edit | edit source]
Plants use water in the photosynthesis process, combining carbon from the air with the hydrogen from the water molecule, and releasing the oxygen from the water molecule. They also use water in their circulation system and to cool themselves when the temperature gets too high.
The relative humidity has a large effect on plants evaporation of water, with plant water use varying 5x over a humidity range of 5% to 95%.
A "ballpark" figure for plant transpiration is roughly 30g/hr/plant of H 2O. A specific example is sorghum, which "consumes" water at the rate of 200:1 (water weight to dry weight sorghum) In addition to the water loss thru the plants, your soil/growing medium will have losses. Aeroponics have virtually no evaporative loss, but poor growth for some plants. In conditions of 50-75% relative humidity and average temperature of 75 F- good plant conditions, an open water surface may evaporate at a rate of 3.2 mm/day. Soil may start at around 4 mm/day until the top soil area is dry, around five days or less, with an eventual drop to around 1.5 mm/day.
If you are using well water, city water, etc. rather than rain water, you are probably adding dissolved salts to your plant growing medium. A general guide is to leach - flood the plant and medium to wash out the salts, every 4 to 6 months. In example, a typical 6 inch pot will hold 10 cups of water, so 20 cups of water are used to leach a plant in such a pot. Keep the water running in a flow to wash out the salts. If the top of the soil has a salt crust, remove it before starting the rinse.
The Arizona Master Gardeners Manual suggests as a watering rate, "…During dry periods, one thorough watering each week of 1 to 2 inches of moisture (65 to 130 gallons per 100 square feet) is usually enough for most soils. Soil should be wetted to a depth of 12 inches each time you water and not watered again until the top few inches begin to dry out. Average garden soil will store about 2 to 4 inches of water per foot of depth." (52 to 104 inches per year). Applied at this same rate year long to a 1,000 square foot garden would require a reliable supply of 33,800 to 67,600 gallons. At 12" annual rainfall and 100% collection rate, the collection area per person needs to be 4,300 to 8,600 square feet.
As long as your home waste water does not contain toxic materials, and is sterlized if containing disease organisms, your garden water supply can include the runoff from your home gray water. Examine the commercial product "Infiltrators". Consider in reverse something like home drain gutters, filled with rock or sand, and buried to route water to the garden areas.
"SOLID" NUTRIENTS[edit | edit source]
Compared to the demand for CO2 and water, the need for other factors is "small", but nevertheless essential.
Plants don't have teeth. Plant roots do not crush substances and eat them. 98% of the nutrients plants absorb with their roots must first be dissolved in the soil water. For nutrients "locked up" in dead plant or animal matter, the cell walls must somehow be ruptured, so the inner nutrients can be reached by the roots. In commercial processing of the algae Chlorella, flash heating is used. In making leaf concentrate, it's a simple blender or grinder. (Blended food scraps anyone?)
Rock dust, or cement kiln dust (before burning) can be applied as a valuable multi-nutrient fertilizer. Logic seems to say that all of the atoms taken from the soil to build the plant end up as either part of my body, or excreted. We're bound to lose some other atoms in our... body gas... perhaps sulfur, but I don't believe it's a lot...
Average pounds produced per person per year. Source: Future Fertility
| Nitrogen | Phosphorus | Potassium | Calcium | |
| Urine | 7.5 | 1.6 | 1.6 | 2.3 |
| Manure | 2.8 | 1.9 | 0.8 | 2.0 |
| Total | 10.3 | 3.5 | 2.4 | 4.3 |
Range required per 100 ft. sq. of garden
| Nitrogen | Phosphorus | Potassium | Calcium |
| 0.1 - 0.5 | 0.2 - 0.6 | 0.15 - 0.50 | 0.2 - 0.8 |
Range one human's effluent can fertilize each year in ft. sq.
| Nitrogen | Phosphorus | Potassium | Calcium | |
|---|---|---|---|---|
| Urine | 1500 - 7500 | 266 - 800 | 320 - 1067 | 287 - 1150 |
| Manure | 560 - 2800 | 316 - 950 | 160 - 533 | 250 - 1000 |
| Total | 2060 - 10300 | 582 - 1750 | 480 - 1600 | 537 - 2150 |
Expect each person to produce around 1 gallon of manure per month, which should be applied to no less than 50 ft. sq. monthly, otherwise you're adding too much nitrogen to the growing medium. Layer manure, then 2" soil, seeds, and sprinkle soil. Move on to next 50 ft. sq., cycle back annually for 3 years, then shift to another set of beds.
Urine must be diluted with water from 5 to 10 to 1.
MACRONUTIENTS[edit | edit source]
The "big three" plants need in their soil are nitrogen (N) phosphorus (P) and potassium (K). NPK are the three numbers you will typically find prominent on fertilizer packages, which refer to the percentage by weight of each. In a 20 pound bag of 21-7-14 it therefore means the bag contains 4.2 pounds nitrogen, 1.4 pounds phosphorus, and 2.8 pounds potassium. Also needed in the soil in relatively large amounts by plants are sulfur, magnesium, and calcium. Green manures add back nitrogen and carbon to the growing medium, but unless you grow them elsewhere and add them to the medium, they can't add any other non-gas element that is not already in the medium, or in the water or fertilizer applied. The remaining macronutrients, carbon, hydrogen and oxygen plants get from air and water.
Nitrogen is a major component of proteins, hormones, chlorophyll, vitamins and enzymes essential for plant life. Nitrogen metabolism is a major factor in stem and leaf growth (vegetative growth). Too much can delay flowering and fruiting. Deficiencies can reduce yields, cause yellowing of the leaves and stunt growth.
Phosphorus is necessary for seed germination, photosynthesis, protein formation and almost all aspects of growth and metabolism in plants. It is essential for flower and fruit formation. Low pH (<4) results in phosphate being chemically locked up in organic soils. Deficiency symptoms are purple stems and leaves; maturity and growth are retarded. Yields of fruit and flowers are poor. Premature drop of fruits and flowers may often occur. Phosphorus must be applied close to the plant's roots in order for the plant to utilize it. Large applications of phosphorus without adequate levels of zinc can cause a zinc deficiency.
Potassium is necessary for formation of sugars, starches, carbohydrates, protein synthesis and cell division in roots and other parts of the plant. It helps to adjust water balance, improves stem rigidity and cold hardiness, enhances flavor and color on fruit and vegetable crops, increases the oil content of fruits and is important for leafy crops. Deficiencies result in low yields, mottled, spotted or curled leaves, scorched or burned look to leaves.
Sulfur is a structural component of amino acids, proteins, vitamins and enzymes and is essential to produce chlorophyll. It imparts flavor to many vegetables. Deficiencies show as light green leaves. Sulfur is readily lost by leaching from soils and should be applied with a nutrient formula. Some water supplies may contain Sulfur.
Magnesium is a critical structural component of the chlorophyll molecule and is necessary for functioning of plant enzymes to produce carbohydrates, sugars and fats. It is used for fruit and nut formation and essential for germination of seeds. Deficient plants appear chlorotic, show yellowing between veins of older leaves; leaves may droop. Magnesium is leached by watering and must be supplied when feeding. It can be applied as a foliar spray to correct deficiencies.
Calcium activates enzymes, is a structural component of cell walls, influences water movement in cells and is necessary for cell growth and division. Some plants must have calcium to take up nitrogen and other minerals. Calcium is easily leached. Calcium, once deposited in plant tissue, is immobile (non-translocatable) so there must be a constant supply for growth. Deficiency causes stunting of new growth in stems, flowers and roots. Symptoms range from distorted new growth to black spots on leaves and fruit. Yellow leaf margins may also appear.
MICRONUTRIENTS[edit | edit source]
There are other elements that while used in much smaller amounts, must nevertheless be present in some "significant" quantity. Essential trace elements include boron (B), chlorine (Cl), copper (Cu), iron (Fe), manganese (Mn), sodium (Na), zinc (Zn), molybdenum (Mo), and nickel (Ni). Beneficial mineral elements include silicon (Si) and cobalt (Co), which have not been deemed essential for all plants but may be essential for some. Eliminate any one of these elements, and plants will display abnormalities of growth, deficiency symptoms, or may not reproduce normally.
Iron is necessary for many enzyme functions and as a catalyst for the synthesis of chlorophyll. It is essential for the young growing parts of plants. Deficiencies are pale leaf color of young leaves followed by yellowing of leaves and large veins. Iron is lost by leaching and is held in the lower portions of the soil structure. Under conditions of high pH (alkaline) iron is rendered unavailable to plants. When soils are alkaline, iron may be abundant but unavailable. Applications of an acid nutrient formula containing iron chelates, held in soluble form, should correct the problem.
Manganese is involved in enzyme activity for photosynthesis, respiration, and nitrogen metabolism. Deficiency in young leaves may show a network of green veins on a light green background similar to an iron deficiency. In the advanced stages the light green parts become white, and leaves are shed. Brownish, black, or grayish spots may appear next to the veins. In neutral or alkaline soils plants often show deficiency symptoms. In highly acid soils, manganese may be available to the extent that it results in toxicity.
Boron is necessary for cell wall formation, membrane integrity, calcium uptake and may aid in the translocation of sugars. Boron affects at least 16 functions in plants. These functions include flowering, pollen germination, fruiting, cell division, water relationships and the movement of hormones. Boron must be available throughout the life of the plant.It is not translocated and is easily leached from soils. Deficiencies kill terminal buds leaving a rosette effect on the plant. Leaves are thick, curled and brittle. Fruits, tubers and roots are discolored, cracked and flecked with brown spots.
Zinc is a component of enzymes or a functional cofactor of a large number of enzymes including auxins (plant growth hormones). It is essential tocarbohydrate metabolism, protein synthesis and internodal elongation (stem growth). Deficient plants have mottled leaves with irregular chlorotic areas. Zinc deficiency leads to iron deficiency causing similar symptoms. Deficiency occurs on eroded soils and is least available at a pH range of 5.5 - 7.0. Lowering the pH can render zinc more available to the point of toxicity.
Copper is concentrated in roots of plants and plays a part in nitrogen metabolism. It is a component of several enzymes and may be part of the enzyme systems that use carbohydrates and proteins. Deficiencies cause die back of the shoot tips, and terminal leaves develop brown spots. Copper is bound tightly in organic matter and may be deficient in highly organic soils. It is not readily lost from soil but may often be unavailable. Too much copper can cause toxicity.
Molybdenum is a structural component of the enzyme that reduces nitrates to ammonia. Without it, the synthesis of proteins is blocked and plant growth ceases. Root nodule (nitrogen fixing) bacteria also require it. Seeds may not form completely, and nitrogen deficiency may occur if plants are lacking molybdenum. Deficiency signs are pale green leaves with rolled or cupped margins.
Chlorine is involved in osmosis (movement of water or solutes in cells), the ionic balance necessary for plants to take up mineral elements and in photosynthesis. Deficiency symptoms include wilting, stubby roots, chlorosis (yellowing) and bronzing. Odors in some plants may be decreased. Chloride, the ionic form of chlorine used by plants, is usually found in soluble forms and is lost by leaching. Some plants may show signs of toxicity if levels are too high.
Nickel has just recently won the status as an essential trace element for plants according to the Agricultural Research Service Plant, Soil and Nutrition Laboratory in Ithaca, NY. It is required for the enzyme urease to break down urea to liberate the nitrogen into a usable form for plants. Nickel is required for iron absorption. Seeds need nickel in order to germinate. Plants grown without additional nickel will gradually reach a deficient level at about the time they mature and begin reproductive growth. If nickel is deficient plants may fail to produce viable seeds.
Sodium is involved in osmotic (water movement) and ionic balance in plants.
Cobalt is required for nitrogen fixation in legumes and in root nodules of nonlegumes. The demand for cobalt is much higher for nitrogen fixation than for ammonium nutrition. Deficient levels could result in nitrogen deficiency symptoms.
Silicon is found as a component of cell walls. Plants with supplies of soluble silicon produce stronger, tougher cell walls making them a mechanical barrier to piercing and sucking insects. This significantly enhances plant heat and drought tolerance. Foliar sprays of silicon have also shown benefits reducing populations of aphids on field crops. Tests have also found that silicon can be deposited by the plants at the site of infection by fungus to combat the penetration of the cell walls by the attacking fungus. Improved leaf erectness, stem strength and prevention or depression of iron and manganese toxicity have all been noted as effects from silicon. Silicon has not been determined essential for all plants but may be beneficial for many.
Micronutrients presence may be difficult to determine. Deliberate initial medium saturation to a pre-determined maximum "safe" level appears a reasonable consideration. In plants, and animals, there are aspects where a single atom of a particular element is essential to the creation or operation of a molecule, and therefore a particular function. No atom, no molecule, no function, no life. Absent high-tech chemistry, any particular missing micronutrient may be difficult to determine. A non-technology approach by observation of the effects on selected plants with known reactions . Rock dust, perhaps preferably dolomitic limestone, but even concrete dust, may contain enough atoms to help.
Whatever you take out of the growing medium, must be replaced. In growing to adulthood, a human will accumulate a collection of elements such as this:
Element Mass of element Element would Mass of element comprise a cube Kilograms this long on a side: oxygen 43 33.5 cm carbon 16 19.2 cm hydrogen 7 46.2 cm nitrogen 1.8 12.7 cm calcium 1 8.64 cm phosphorus 0.78 7.54 cm potassium 0.14 5.46 cm sulfur 0.14 4.07 cm sodium 0.1 4.69 cm chlorine 0.095 3.98 cm magnesium 0.019 2.22 cm iron 0.0042 8.1 mm fluorine 0.0026 1.20 cm zinc 0.0023 6.9 mm silicon 0.001 7.5 mm rubidium 0.00068 7.6 mm strontium 0.00032 5.0 mm bromine 0.00026 4.0 mm lead 0.00012 2.2 mm copper 0.00000072 2.0 mm aluminum 0.00000006 2.8 mm cadmium 0.00000005 1.8 mm cerium 0.00000004 1.7 mm barium 0.000000022 1.8 mm iodine 0.00000002 1.6 mm tin 0.00000002 1.5 mm titanium 0.00000002 1.6 mm boron 0.000000018 2.0 mm nickel 0.000000015 1.2 mm selenium 0.000000015 1.5 mm chromium 0.000000014 1.3 mm manganese 0.000000012 1.2 mm arsenic 0.000000007 1.1 mm lithium 0.000000007 2.4 mm cesium 0.000000006 1.5 mm mercury 0.000000006 0.8 mm germanium 0.000000005 1.0 mm molybdenum 0.000000005 0.8 mm cobalt 0.000000003 0.7 mm antimony 0.000000002 0.7 mm silver 0.000000002 0.6 mm niobium 1.5E-09 0.6 mm zirconium 0.000000001 0.54 mm lanthanium 8E-10 0.51 mm gallium 7E-10 0.49 mm tellurium 7E-10 0.48 mm yttrium 6E-10 0.51 mm bismuth 5E-10 0.37 mm thallium 5E-10 0.35 mm indium 4E-10 0.38 mm gold 2E-10 0.22 mm scandium 2E-10 0.41 mm tantalum 2E-10 0.23 mm vanadium 1.1E-10 0.26 mm thorium 1E-10 0.20 mm uranium 1E-10 0.17 mm samarium 5E-14 0.19 mm beryllium 3.6E-14 0.27 mm tungsten 2E-14 0.10 mm
If it's not in the growing medium, it won't be in the plant, or in you. Take "Popeye's" favorite, spinach and the iron that is to make him strong. Organic grown / virgin soil spinach has around 1584 PPM iron. From commercial farms, it's 19 PPM. About 1% of nature.
LIGHTING[edit | edit source]
Most plants cannot use the entire spectrum or intensity of light received on Earth. Limiting the light intensity and frequency to that at which each type of plant best grows reduces the heat load. Plants may also have specific lighting duration periods. Periods shorter than daylight can easily be simulated by shutters. Plants needing longer light periods than available daylight can often be "tricked" into continued processing though by low intensity artificial light, well below normal growing levels. In low light areas more useful light for the plants is gained where the growing area is mirrored, or reflecting in the right frequencies. Most plants need light in wavelengths of 400 to 700 nm, which I read is 45% of incoming light. They apparently do best in red and blue light. When growing vegetative matter, plants use primarily blue-violet light. When flowering they need red-orange end of the spectrum. As an aside, human eyes see green best, a color little used by plants, which reflect it and therefore they appear green to us. Terms often used to describe light are Lumen, Foot-Candle, Watt, and Lumens per Watt. Lumen is a particular amount of light energy. Envision a ton of feathers, it doesn't matter whether they fill a room, or are compressed into a brick, it's still a ton. Foot Candle measures light intensity. It is one lumen of light shining on one square foot. Watt is an electrical term. As we see with the difference in incandescent and fluorescent bulbs, watts of electricity IN, does not necessarily mean the same light OUT. It is a convenient means of comparison though of power in sunlight, in p/v panel conversion, and bulb conversion. Lumens per Watt is the efficiency of a bulb in converting electricity to useful light.
In some situations, such as climates with extreme exterior temperature challenges, it may be necessary to consider use of p/v panels to generate electricity, for lighting and plant growth in remote, strictly environmentally controlled chambers. (Of course, you need a lot of money to set this up.) Perpendicular direct daylight is around 10,000 lumens per square foot, for ease of estimating call it 100 watts if perfectly converted to electricity. In modest cloud cover, light intensity can drop to 1/10 or less. My reading shows that this may be the minimum power level for most photosynthesis. (Compare though to the Columbia University folks - Vertical Farm - who estimated a general value of 25 watt per meter square (2.32 watt foot square) for plant lighting. Plants convert certain frequencies of light into simple sugars. Too little light, and photosynthesis will not take place.
The "open" blue sky provides around 16% of useful light to plants of the intensity of direct sun. Too much light, and the plant overheats, transpires greatly increased water flow, and photosynthesis may not only shut down, but the plant may start to burn the sugars.
Sunlight is basically 10% U/V, 45% visible, 45% infrared (near/heat, and far/useable by plants). Most vegetables can use only make use of captured light up to a maximum of 2,500 - 5000 footcandles, and need this intensity for a period of about 6 hours daily, or about 15,000 to 30,000 foot candle hours of light. (Some vegetables, such as parsley, lettuce, chives, radishes and cabbage can do well with 4 hours.) (Intensity will vary depending on your latitude, time of year, atmospheric conditions, etc.)
Depending on your local conditions, you may be able to grow some plants in partial shadow, or your plants may benefit from some artificial reduction in light intensity. If read that for most plants, the "ideal" wavelength of light is red, with the plant maintained at an optimum temperature of 77 degrees F (25 C). If you intend to use artificial lighting to drive, or aid, your growing area, then bulb light production efficiency is a major issue.
A regular 100 watt household light bulb produces only around 400 lumens, or about 4 lumens per watt. If you used mirrors and focused it all on one square foot, it would be around 4% of open sunlight. Halogen bulbs produce about 20 lumens per watt, 100 watts being 20% of open sunlight.
Fluorescent bulbs, say high output, full-spectrum bulbs produce 68 lumens per watt, 100 watts being 60% of open sunlight.
Metal Halide Lamps are often used in hydroponic labs, they produce 80-120 lumens per watt, 100 watts being essentially the power of open sunlight. High Pressure Sodium lamps produce somewhere between 90 to 150 lumens per watt, or again the power of open sunlight. At these efficiency levels, perhaps frequency becomes more important. (See discussion of frequency applicable for the plants stage of life.) Electrical conversion is not the only consideration. In long-term sustainability, the lifespan of a product, and ability to replace it, becomes far more important than energy conversion efficiency. Another factor is AVOIDING loss of useful light frequency. Mentioned elsewhere, light absorbed and re-emitted comes out in a longer, often less useful frequency. Line your growing chamber with foil, or mirrors. Cited on the web for reflective efficiency is Foylon, (see also Aluma-Glo) at 97% reflectivity. LET THERE BE (A SELECTED SPECTRUM) OF SUNLIGHT A brief digression into a science summary, if you will bear with me. Visible light is just one small portion of the wavelength spectrum for electromagnetic energy. Below visible light is ultraviolet light, then X-rays. Above visible light is infrared (heat) then "radio" waves. From low to high (400 to 700) the colors go something like violet, blue, blue-green, green, yellow-green, yellow, orange, red. The longer the wavelength of light, the longer it takes for the photon's energy to be imparted on whatever it strikes.
Think a quick punch (short wavelength & duration of impact) vs a slow push from the same arm (long wavelength long duration of impact). less "energy" a given photon has. If a particle absorbs a photon, it is either absorbed as heat, triggers a chemical reaction (causes an electron to move) or is re-emitted as a longer wavelength.
Chlorophyll A plants prefer blue 430 nm & red 66 nm Chlorophyll B plants prefer blue 460 nm & orange 640 nm Carotene prefers 400 nm to 500 nm.
High tech selective surfaces can provide a means to eliminate the unwanted frequencies. These items though tend to be expensive, fragile, and derived from finite fossil fuels. Consider a more "robust" and local hardware store approach.
I'm working at a latitude of around 32 degrees north - recalculate all angles for your latitude, with a goal of blocking direct summer heat, yet passing the maximum level of blue and red light. In winter my noon sun is 34.5 degrees up from true South, and 81.5 degrees in summer.
Envision thin strips of shiny red on the top, mirrored on the bottom. Have the slats runs true East / West, each tilted up 30 degrees. Set the North / South space between slats such that direct sunlight from 60 degrees or higher cannot pass.
The following two photographs are of the same "ceiling", located in Phoenix, Arizona. The first is looking at the ceiling toward the direction of summer morning sun, the slats blocking most summer noon sun. Shading in the picture disguises the true angles of the slats, which show better perhaps in the lower photo, which is looking toward the winter pre-noon position.
My proposal is a set of slats similar to this, but instead of all white, a combination of bright red and mirror.
In the winter most of the sun either directly passes or strikes the mirror and is reflected to the growing area. In the summer almost all direct sun strikes the red, which is then reflected down by the mirror. Around a 60 degree swath of diffuse blue sky is always available to the plants directly, or reflected down.
The below photo is essentially looking due east.
A simpler approach than the welded overlapping metal used at the Phoenix location would be two separate layers of slats, which could also allow them to be made adjustable if desired. Simpler yet is recognition that the east-west running slats are the priority. Simple short lifespan slats can be bright cloth and mylar held by a pattern of ropes.
If desired at the lower edge of the red side of the (fixed) slats a transparent substance (glass, plastic, ?) could be attached and extended perpendicular to the slat, making contact with the parallel mirror surface, or not, as desired. It would block most air flow thru the slats, and catch & channel most rain that fell on this roof.
PHOTOSYSTHESIS EFFICIENCY[edit | edit source]
Plants use light to rearrange molecules to store solar energy as chemical energy in the form of starch and glucose (sugar). The present globally photosynthetic atmospheric processing limit appears to be 2 x 1017 grams of carbon (200 billion tons) per year, which is about 10% of the atmospheric content. This carbon is being used by organisms and returned by respiration. We humans with our increasing numbers, burning ancient stored carbon, and depletion of plant mass are raising carbon levels. In plant cells water and carbon dioxide enter the cells, and impacted by the right frequency and intensity of light, sugar and oxygen leave the leaf. The chemical equation for this process is:
6CO2 + 12H2O + 48 photons light → C6H12O6 + 6O2 + 6H2O
6 molecules of carbon dioxide (6CO2) and 12 molecules of water (12H2O) are consumed in the process, while glucose (C6H12O6), six molecules of oxygen (6O2), and six molecules of water (6H2O) are produced.
Plants have limits on their rate of converting light to stored energy. Remember that plant biological processes continue at night, and that this uses up some of the energy accumulated in the presence of light. I've read that the overall theoretical efficiency of photosynthesis may be 4.5%. At 6 hour exposure, and if you could eat the entire plant, this would be an area 9 feet on a side. I've no idea what the crop would be, but you would probably be able to watch it grow…
If this "perfect" rate were potatoes, production would be (86 mt dry or 346 mt fresh) / ha). The real-world yield is (12 mt dry or 29 mt fresh) /ha, less then 1/10 of theoretical.
In various sources I find that overall photosynthesis efficiency in open nature and for typical food crops (corn,wheat,rice) is .1% to .2%. For 1/10% efficiency, each of us requires 21,600 sq. ft. /hours per day. With an average of 6 hours solar exposure per day this requires a fully productive food crop area of 3,600 sq. ft., 1,800 for 2/10% This is an area much less than the 1/4 acre per person typically available for manual farming (see information on farming in Cuba post-USSR), yet higher than the 1,000 sq. ft. information from Ecology Action. More (concentrated) sun is not the answer. C3 crops (wheat, barley rice, sugar beet, potatoes) all have FALLING conversion efficiency rates as light intensity goes above 20% of full sunlight.
Potato efficiency goes up to .4%, so with 6 hours exposure you need a minimum of 900 sq. ft. In various places, I've read the most "efficient" crop is claimed to be spirulina, with production of between 5 and 15 gram per sq. yd. per day. If each gram is around 5 calories, we get somewhere between 243 ft. sq. to 720 ft. sq. per person. At the upper level of production, is we're still assuming an average of 6 hours good sun exposure, we're looking at just under 2% efficiency on converting sunlight to food energy.
While I do not really expect to find a more efficient crop than algae, perhaps hydroponic or aeroponic methods can bring up the efficiency of more traditional foods. For those with a sweet tooth, Sugar cane (a C4 crop) comes in at a yearly average of 1%, requiring 360 sq. ft. with 6 hours sunlight, and with crops such as corn and sorghum can utilize higher sun intensity.
REDUCED LIGHT[edit | edit source]
Studies in Israel show increased growth of young citrus trees under reduced mid day light in a semi-arid climate, using up to 60% shade cloth. With too much light, some plants shut down photosynthesis, and physically "wilt" their leaves to minimize light exposure. Shade particularly benefits plants grown for their leaves.
The photosynthesis rate increase tracks increased intensity of direct light only from 0 to 50 watt per meter sq., then increased production tapers slightly up to 100 watt, and for many plants goes almost flat at 200 watt per meter sq.
I also read of plants benefiting from flickering light, vs constant. Perhaps a means to disperse sunlight as momentary sparkles would allow a greater growing area than the available solar window (welcome back the disco ball?).
Consider methods that rather than block a portion of the light, rather split the light into 2 or more separate beams. Route each beam via mirrors, lenses, fiber optic, etc, to separate, perhaps stacked growing areas, then diffuse each beam so that it illuminates an area of plants equal in area to the original light collection area. Do we accomplish the reduced sun that many plants need, while doubling or more the growing area?
At a minimum, line the growing area with reflective material, and perhaps you can "recycle" some of the light that otherwise would escape back to the sky, or just go to heat the surrounding area. A reflective northern wall may add as much as 12.5% "extra" light.
LIGHTING PERIODS[edit | edit source]
Plants that genetically need specific lighting periods and be "tricked" in to acting as though there is a longer or shorter photo tropical period. Shorter is easy, you just need an opaque cover. The "trick" is making their genes think that daylight is longer. At the mid-darkness period, provide artificial light of 10 to 30 foot candle for times such as 3 minutes in every 30 minutes, 6 seconds in every minute.
A 40 watt florescent tube power is:
Inch Distance Ft. Candle
| Inch Distance | Ft. Candle |
|---|---|
| 1 | 1000 |
| 2 | 950 |
| 3 | 750 |
| 4 | 650 |
| 5 | 560 |
| 6 | 400 |
| 7 | 430 |
| 8 | 370 |
| 9 | 360 |
| 10 | 350 |
| Plant | Watt/Ft.Sq |
|---|---|
| Tomato | 8.3 |
| Eggplant | 2.32 |
| Peppers | 2.32 |
| Soybeans | 2.32 |
| Green peas | 2.32 |
| Spinach | 2.32 |
| Carrots | 2.32 |
| Cucumbers | 15.77 |
| Wheat | 2.32 |
| Lettuce | 2.5 |
| Strawberries | 7.06 |
TEMPERATURE CONTROL[edit | edit source]
Earth berming or burying a contained growing area would minimize the effect of external temperature variations, and provide greater pest protection. Earth sheltering combined with insulation should, if the intrusion of heat is avoided, provide for appropriate year round temperatures. Unless intended / used as human shelter for a CBR threat, the structure does not need to be airtight or constantly overpressured.
Root temperature in general should not exceed 82 degrees F, above which growth processes drop off, with 68 to 77 preferred. A root zone temperature of 105 degrees F is probably fatal to most plants. Leaves usually prefer 61 to 68 F.
GROWING AREA[edit | edit source]
Readily available information suggests that 1,000 sq. ft. minimum of growing area is needed per person. With a typical modern diet, the upper fertilizing limit for humanure looks to be around 1600 ft. sq., with the limiting nutrient being potassium, and a potential "minimum" area of 600 ft. sq. based on a nitrogen concentration limit.
In the interest of pest control, I would not suggest a single large facility for a family. Instead, a number of separate units would permit growing a wider variety of plants, in differing conditions, concentrated with other plants needing similar conditions. It may also be simpler and cheaper to make a series of smaller units even per person, rather than a single 600 to 1,600 sq. ft. "greenhouse" for each person.
The commercially available concept and products that blend well with the MESS concept are those intended for "roof gardens", and their design factors. A bottom water proof membrane and roof penetration protection, a layer of drainage and aeration, a means to prevent soil penetrating the drainage, and compost above. Protect the top of the soil with another aeration barrier, then wind barrier above, which has penetrations for plantings. Weight is a major consideration in a roof garden or say gardening in containers on raised benches.
If your gardening media is enclosed and suspended above ground, then consider if you can walk under the garden. How far can you lean and reach if you are tending the garden? If you can walk under, and come up thru san a square 2' on a side to tend by leaning, then you eliminate a lot of waster path space. If you can reach 3 foot (or a hair more) then think in terms of each 8' x 8' growing area having a 2' x 2' hole in the middle. Each 64 sq.ft. of surface area has 60 sq.ft. of growing space. If you "fudge" the math a bit (remember, the growing area can be from 1,000 to 1,600 sq. ft), you could have these units in a grid either 4 or 5 on a side. This is a A square with sides between 32' and 40'. (Is there a commercially available bubble 8' x 8'?) If a single test facility for your area is to have just plants on benches without walk-under capability, the above therefore would put a single test unit at around 8' x 12".
The bulk of my container tinkering was in "Wal-Mart" plastic tubs setting on cheap steel shelves. (Which of course rusted-out in a few short years.) "Rubbermaid" heavy duty shelving costs more, but in the 4th year of outdoor use shows no signs of decay.
The growing level. A mix of composted biomass and inert water holding substances. The depth will vary depending on the crop. The medium must hold surface tension water, yet drain well and allow air into the "pores" between particles.
Next down is a drain / filter level, I use fiberglass garden cloth, some of which has been in use for 5+ years (2007). Under this is 1 to 3 inches of "volcanic" rock, light but it holds the filter above the water and provides air space.
Under the rock I've been having success with another layer of fiberglass cloth as a wick, and keeping an upside down bottle, down thru a sleeve to keep the wick wet.
The greater the control & isolation from external influences, the better. But, your facility can be anything from a hedge rimmed garden to a miniature version of the Biosphere II facility, or the NASA CELESS. It's up to you and your resources. If you want to exclude excess heat (my situation most of the year) the only light to reach the garden should be that intensity and frequency needed by the plant, all else is waste heat. Insulate and protect the growing medium from light and moving air.
HUMIDITY RECOVERY[edit | edit source]
At the moment, short of a sealed greenhouse and running mechanical HVAC, I'm unclear on a method. (See Appropriate Technology - Dew Collection) I've read of fans blowing air from above the plants thru buried porous pipes, with the lower ground temperature leading to condensation, then the water draining from the pipes.
If the greenhouse IS sealed, then the largest challenge is getting heat OUT of the plant growing structure. Consider a bottle top up filled with water inside the greenhouse, another empty one outside top down, and the mouths of the bottles connected by hose. If the bottles and hose are solid enough, the temperature of evaporation can be "set" by controlled imposition of a vacuum on the unit. When the temperature of the inside bottle is greater than that of the outside bottle, water will evaporate, the vapor flow then condense, and the liquid water run back .
WATSON WICK WARNING CHECK WITH YOUR LOCAL HEALTH OFFICIALS A method of recycling human effluent rather directly to the growing medium is the Aerobic Pumice Wick presented by TOM WATSON. Black water drains thru a filter tank to hold solids for aerobic composting, allowing the liquid to drain to a bed/tank. In this container you want a lot of wicking material, with a lot of air. Mr. Watson suggests an 18" bed of pumice in a waterproof base, with a cover of around 6" of soil. The bottom 1/2" to 1" needs to be water-tight. Absent pumice, consider coarse sand. Without a watertight membrane, use the old approach of a layer of straw and manure to help anaerobic bacteria create a water impermeable "clogging" layer. The intent is to create an area to convert the smelly end product of human digestion, which scientifically can be seen as 0.16 g/l dissolved solids, 0.23 g/l suspended solids, 0.007 g/l phosphate, and 0.51 g/l nitrogen, into a nutrient righ garden bed. Plant roots access the bed use the nutrients and transpire the water. In the case of too much liquid, the wick acts as a filter and filtered water drains out of the exit pipe. Please ensure liquid does not rise to the compost level.
Perennial plants are best used because of their permanent roots. Lawns, shade trees, fruit trees, berries, grape arbors etc. are all suitable as there are no disease vectors transmitted via the roots. WARNING CHECK WITH YOUR LOCAL HEALTH OFFICIALS AIR STORAGE
If used as a CBR shelter, air storage is needed to avoid drastic swings in air composition. Consider the earth, with plant and animal activity taking place on the surface or in the first 100 feet or so, yet with miles of effective storage overhead. A potential methods to combine the garden with a large sealed volume of air is a rooftop garden over your sealed home.
PLANTING PLANNING[edit | edit source]
Companion planting . Some plants grow better together, or immediately following each other, while some plants cannot tolerate each other or growing in a medium just after other particular plants. Nitrogen Replenishment. Nitrogen fixation may be accomplished by symbiotic organisms of legumes, or other plants which harbor the correct microbial population. Plants can not fix nitrogen gas but legumes have evolved a symbiotic relationship with the bacteria of the genus Rhizobium, which grow in special nodules in those plants. The plant provides the bacteria with the nutrients they need for growth and in return obtain nitrogen which the bacteria convert from N2 into NH4+. These nitrogen fixing crops should preceed heaving nitrogen feeding crops. Nutrient Concentrations. The life cycle of plants, animal intervention, earthworm or microbe systems may cause temporary concentrations (therefore also temporary areas of shortages). Overages or shortages can be tested in a non-technology manner by selected plantings and ovservation of the plant reactions. Crop cycling. In addition to companion planting, keeping a growing range from seed to mature plants, based on the needs of he plants and your consumption rate. For example, if you use a head of lettuce every week, you need to plant lettuce weekly. For every plant completely harvested you should have it's replacement already growing and ready to set out. Cycle planting also includes considering that there are plants which cannot tolerate being in the growing medium immediately after certain other plants. Seed Crops. You'll want to keep seeds of the "best" plants for your next generation.
Cloning. Many plants can be cloned from cuttings, or with the right technology from far smaller portions than would happen in nature. A large enough genetic base, in the form of stored seeds, needs to be maintained to prevent deleterious mutations being concentrated due to inbreeding or cloning of the "defective" plant.
A "Grocery Store" recipe for cloning "difficult" plants is 1/8 cup sugar, 1 cup water (or coconut milk), 1/2 cup pre-mixed water and fertilizer, 1/2 inositol (125mg) vitamin tablet, 1/4 vitamin tablet with thiamin, 2 tablespoon agar flakes (or corn starch, jello, etc.)
The growth promoting substance in plant shoot tips will, if the tips are crushed, diffuse into surrounding substances, and therefore be collectible in substances, such as galatin.
Plants being rooted may not be able to manufacture their own "food. They may be helped along by sugar water, coconut milk, fruit juices, etc.
ALGAE CULTURES[edit | edit source]
Algae grows quite well naturally in most ponds and ditches, taking its carbon dioxide from the water plus utilizing what minerals are in the water. Logically if you harvested a portion each day and minerals were added, the crop would be much larger than it is naturally. Potentially three foot wide, 20 feet long, one foot deep plastic-lined troughs filled with the water could supply all the algae wanted.
For animal feed, the harvested algae could be mixed with the dead flies, dried and pelletized or broken up. As chicken feed it would supply all the protiens, vitamins and minerals required, even by chicks. For human consumption, Spirulina is sold as a health food. While I'm not enthused by the taste, I had Spirulina growing for several years from a starting of commercially available supply. As part of it's nutrient source, I pour water thru local sand, and potting soil.
Spirulina, a one-celled form of algae, perhaps a "link" between plants and animals, thrives in slightly saline "fresh" water, 8 to 11 pH, of 85 to 112 degrees F, up to 140 degrees F. The conditions are such that most other microorganisms cannot survive. It is perhaps the most "efficient" means to grow a nutritious food, which is over 65% complete protein, that is all essential amino acids in balance. It is 8 to 10 percent efficient in use of light, and is one of the few plant sources of vitamin B12, usually found only in animal tissues. A teaspoon of Spirulina supplies 250% of the Recommended Daily Allowance of vitamin B12 and contains over twice the amount of this vitamin found in an equivalent serving of liver. It also provides high concentrations of many other nutrients - amino acids, chelated minerals, pigmentations, rhamnose sugars (complex natural plant sugars), trace elements, enzymes - that are in an easily assimilable form.
Certain desert-adapted species will survive when their pond habitats evaporate in the intense sun, drying to a dormant state on rocks as hot as 70 degrees Centigrade (160 degrees F). In this dormant condition, the naturally blue-green algae turns a frosted white and develops a sweet flavor as its 71 percent protein structure is transformed into polysaccharide sugars by the heat.
The blue-green algae, and Spirulina in particular, have a primitive structure with few starch storage cells and cell membrane proliferation, but rich amounts of ribosomes, the cellular bodies that manufacture protein. This particular arrangement of cellular components allows for rapid photosynthesis and formation of proteins. The lack of hard cellular walls assures that Spirulina protein is rapidly and easily assimilated by consuming organisms.
Any water-tight, open container can be used to grow spirulina, provided it will resist corrosion. Its depth is usually 16 inches (twice the depth of the culture itself). Temperature is the most important climatic factor influencing the rate of growth of spirulina. Below 68°F growth is practically nil. The optimum temperature is 99°F, but above 108°F it is in danger. Growth takes place in light (photosynthesis), but illumination 24 hours a day is not recommended. It cannot stand a strong light when below 68°F. It preferes 1/3 of full sun, with cells destroyed by prolonged strong light.
The water used should be clean or filtered, but consider it's natural conditions.
When in good condition harvesting is an easy operation, but when it gets "sticky" harvesting may become a mess. Harvesting in early morning for the cool temperature, more sunshine hours to dry the product, and the % proteins in the spirulina is highest in the morning. Harvest by a filter of a fine weave cloth.
The nutrients extracted from the culture medium by the harvested biomass must be replaced. The major nutrients can be supplied in various ways, preferrably in a soluble form, but even insoluble materials will slowly be disolved as the corresponding ions are consumed by the spirulina in the medium. Urea is an excellent nutrient for spirulina but its concentration in the medium must be kept low (below about 100 mg/liter). If sugar or other easily oxidizable organic materials are used as a source of carbon, nitrates cannot be fed in large concentration either, as they may be reduced to ammonia that is toxic above 150 mg/liter. Excess urea can be converted either to nitrates or to ammonia in the medium. A faint smell of ammonia is a sign that there is an excess of nitrogen, not necessarily harmful ; a strong odour however indicates an overdose. Balance salinity at 15 grams per liter and alkalinity at 0.1 N
Per liter based on chemicals: NaHCO - 8 gram (sodium bircarbonate) Sea Salt - 5.0 NaNO3 or KNO3 2.0 or Urea - 0.07 NH4H3PO4 - 0.1 K2SO4 - 0.1 MgSO4*7H2) - 0.1 FeSO4 - 0.001
Natural approach: Use ashes from wood fires rich in potassium, sea salt, urine, and iron such as from old nails with vinegar and lemon juice. Blood also is a good source of iron. In case of necessity ("survival" type situations), all major nutrients and micronutrients except iron can be supplied by urine (from persons or animals in good health, not consuming drugs) at a dose of about 15 to 20 liters/ kg spirulina. Iron can be supplied by a saturated solution of iron in vinegar (use about 100 ml/kg).
Freshly harvested and eaten is best, it will not keep more than a few days in the refrigerator, and no more than a few hours at room temperature. Adding 10 % salt is a good way to extend these keeping times up to several months, but the appearance and taste of the product change : the blue pigment (phycocyanin) is liberated, the product becomes fluid and the taste is somewhat like anchovy's paste. Freezing is a very convenient way to keep fresh spirulina for a long time. It also liberates the blue pigment, but it does not alter the taste. Drying is the only commercial way to keep spirulina. If suitably packaged and stored, dry spirulina is considered good for consumption up to five years. But drying is an expensive process and it very generally gives the product a different and possibly unpleasant taste and odour. Dried spirulina is also not so easy to use.
Direct sun drying must be very quick, otherwise the chlorophyll will be destroyed and the dry product will appear blueish. Whatever the source of heat, the biomass to be dried must be thin enough to dry before it starts fermenting. Drying temperature should be limited to 158°F, and drying time to 5 hours.
AQUACULTURE[edit | edit source]
Fish present a means to "process" bugs, worms, etc. into a pleasing protein source. Tilapia do well in small captive tanks, and in fact may breed too well, with an exploding population of a LOT of small fish with few bigger (and more eatable) fish. Think of them as producing liquid fertilizer.
Tilapia have been successfully grown in a 725 gallon tank, catfish in 55 gallon drums. In such crowded conditions, 10% or more by volume must be siphoned out monthly from the bottom sludge.
Tilapia is a hearty freshwater fish native to the Middle East and Africa which grows rapidly within a range of environments, with a high tolerance for bad conditions including relatively low oxygen and high silt, with a diet that can include algae, agricultural "waste", or bugs (see notes elsewhere on fly-farming). The growing fish must be fed roughly one and one-half times their average daily body weight throughout the course of their lives. They have 19.7 g protein and 2 g fat per 3.5 oz (100 g) serving. Tilapia need warm-water from 82° to 86°F. They need minimum dissolved oxygen level of 3 parts per million, requiring some pumping system in a crowded tank. Tilapia grow best in water with a pH of 7; as nitrogenous wastes (urea, uric acids) build up and make the water acidic, neutral pH is maintained by added buffers such as KOH or (Ca(OH)2), added daily or every other day. Iron is supplied through the addition of an iron chelate once every three weeks and the recommended amount is 2ppm.
Each individual fish (harvested at .45 kg or 450 grams), would consume 2.5 times that amount, or 1,125g, of which 40% becomes increased body mass, 20-30% is used for energy and maintaining body functions, and 30-40% is waste. Our 10 person homestead tank would require fish feed of 1,125 kg, in order to reach the target weight.
Fish waste products of urea and solid excrement accumulate in the tanks, which must be removed and recycled to the growing plant crops, including algae as fish food.
The Columbia study shows one tank 8' in diameter by 4' deep (1,250 gallons) can be stocked with 800 30g male tilapia fingerlings grown for 6 months before harvest, even with a high mortality of 25%, fish harvested at 450 grams, edible filets of 40% of live weight. With 600 surviving fish at 450 g per fish, one tank harvest should provide .45kg x 600 = 2700kgs x .40 = 108 kg edible fish. This is an average of around 600 gram of fish flesh per day. (To feed six people) Our target per family size is 10 people, so we need a tank that is 160% larger in volume, and twice again the area to provide for a full year. Their example tank is around 200 cubic feet. Each homestead needs about 640 cubic feet (4166 gallon), which weighs around 33.332 pounds (don't put it on the roof with a LOT of reinforcement). If we keep the same depth as the Columbia example, then the diameter must increase to around 10 feet. The size of each of the two tanks is still not much more than an above ground kid pool.
