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2.0 Hydroponics - the solution to the food problem

      
       Hydroponics offers the promise of feeding the millions of
   starving people around the world.  Many greenhouse operations are
   actually hydroponic in nature - that is they are merely called
   "greenhouses" whereas they should really be called hydroponic growing
   facilities. Some of the high yields we refer to are greenhouse results
   however, since in both cases the crops are enclosed and protected
   from insects and the weather, we consider them interchangeable.
       Hydroponic and greenhouse yields are commonly 5 times the
   field yield for a two crop per year field harvest and 10 times the
   field yield for a one crop per year field harvest.  In one case
   the Whittaker Corporation's Agri-Systems division in Somis, CA. has
   achieved an absolutely astounding 100 times the field yield of
   Bibb lettuce in their 2.5 acre facility [57, p.147-151].  The
   normal field yield is about 30,000 heads per acre, but they grow
   an amazing 3.2 million heads per acre per year [57, p.150].
       Hydroponics is the science of growing plants without soil.
   The crops are not actually grown in water unless it is oxygenated
   because the roots need oxygen.   Crops are usually grown in some
   inert medium such as sand, gravel, Perlite, or Vermiculite. In
   space we will have no soil and we must use the lightest weight
   medium possible.   Perlite weighs only 5 to 8 pounds per cubic
   foot and since it has no cation exchange capacity it will not
   interfere with our nutrient solutions [57, p.271].
       Sometimes the roots are allowed to hang down in the air and
   sprays or mists are used to wet the roots with the nutrient mixture.
   The many and varied techniques will not be reviewed here.  For an
   excellent treatment the interested reader is referred to
   "Hydroponic Food Production" by H.M. Resh published by Woodbridge
   Press, third edition in 1987 [Ref 57].  In any case, the roots
   are periodically soaked in a water-based nutrient mixture which
   contains a very carefully selected blend of dissolved chemicals
   which provide the food elements that the crop needs.  Of course
   different plants require somewhat different nutrients, but the
   common elements are needed by all.  The following 16 elements
   are considered essential to the growth of higher plants [84, p.194].
*      Element      Atomic  Atomic   % of dry
                    Symbol  Weight   plant tissue
       Carbon         C      12.01   45
       Oxygen         O      16.00   45
       Hydrogen       H       1.01    6
       Nitrogen       N      14.01    1.5
       Potassium      K      39.10    1.0
       Calcium        Ca     40.08    0.5
       Magnesium      Mg     24.30    0.2
       Phosphorus     P      30.97    0.2
       Sulfur         S      32.06    0.1
       Chlorine       Cl     35.45    0.01
       Iron           Fe     55.85    0.01
       Manganese      Mn     54.94    0.005
       Boron          B      10.81    0.002
       Zinc           Zn     65.38    0.002
       Copper         Cu     63.55    0.0006
       Molybdenum     Mo     95.94    0.00001
       Sources: [84] F.B. Salisbury, C.Ross, "Plant Physiology",
          Wadsworth, 1969, p.194. ( except atomic weights )
          [70] "The 1990 Information Please Almanac", 1990,
          p.532-533. ( atomic weights )
.
   2.1  Factors which effect yields
       Naturally one is curious as to why the yields are so much
   greater for hydroponic or greenhouse produce than for field
   crops.  We shall review some of the most important factors
   individually.
       The most important factor is plant spacing or plant
   density.  Plant density is increased in one or more of the
   following ways: (1) grow plants closer together, (2) eliminate
   extra walk space between rows, (3) train plants to grow vertically
   instead of horizontally, and (4) grow plants in layers.  It appears
   that Whittaker Corp has employed methods (1),(2), and (4).  They
   tested up to 5 layers but settled on two [57, p.147].  They do not
   use articifial light so that means the density could be increased
   without limit through the use of artificial light and more layers.
       Given that an acre contains 43,560 square feet, it is clear
   that a field yield of 30,000 heads per crop (which is only about 2/3
   of the crop planted) is about one head per square foot.  That is a
   spacing of 12 inches in each direction.  By reducing the spacing to
   6 inches in each direction you multiply the density by four.  And by
   adding a second layer you multiply the density by eight.
       Gurney's gives the spacing for cucumbers as 6 feet between
   rows and 4 feet between plants [78, p.4].  Greenhouse crops of
   cucumbers are trained to grow vertically thus taking much less
   space per plant.  How much less?  A spacing of 24 inches in each
   direction gives an increase in density of 3 times 2 or a
   factor of 6.
       Gurney's gives the spacing for tomatoes as 4 feet between
   rows and 4 feet between plants [78, p.4].  Tomatoes grown in
   greenhouses in Abu Dhabi and elsewhere are trained to grow
   vertically.  A spacing of 24 inches in each direction gives an
   increase in density of 2 times 2 or a factor of 4.
       Gurney's gives the spacing for squash as 8 feet between rows
   and 8 feet between plants [78, p.4].  Again by training them to
   grow vertically and using a spacing of 24 inches in each direction,
   the density increase factor is 4 times 4 or a factor of 16.  Let us
   summarize these results.
*      Crop            Density increase factor
       --------        --------
       Bibb lettuce        8
       Cucumbers           6
       Tomatoes            4
       Squash             16
.
       The second most important factor in increasing yields is the
   number of crops per year.  Many field crops have only one harvest
   per year.  A few crops have two harvests per year, such as broccoli
   or carrots, but rare is the crop with more than two harvests per
   year (radishes 3 to 4 or bean sprouts - many).  The obvious reason
   for this is the weather.  Frost either late in the spring or early
   in the fall will kill most fruits and vegetables.  Since greenhouse
   and hydroponic crops are grown indoors, their crops can be grown
   all year long.  This means that you can have four 90 day crops
   per year or five 70 day crops or twelve one-month crops etc. Let
   us summarize these results.
*      Crop         Crops per year   Yield factor
       --------          ------    ------
       Bean sprouts       26.0       2-3
       Radishes           12.0       2-3
       Bibb lettuce        8.0       4-8
       Beets               6.0       3-6
       Peppers             5.0       2-5
       Tomatoes            4.0       2-4
       Parsnips            3.0       2-3
.
       Thus, depending upon your local growing season, this can
   mean an increase in the yield by a factor of from two to eight
   or perhaps more.
       The third most important factor in increasing yields is
   the particular variety of crop you plant.  This has at least
   three effects: (1) the amount of produce per plant per crop,
   (2) the number of crops per year (i.e. faster maturing
   crops allow more crops per year), and (3) the space required
   by each plant.  Clearly these effects may not all work in
   your favor in the same crop.  For example, Gurney's 1990 catalog
   offers over a dozen varieties of tomatoes [78, p.16-17].  The
   time to maturity varies from 45 to 90 days.  Obviously this means
   twice as many crops per year with the former variety.  One variety
   is claimed to produce 50 pounds of tomatoes per plant!  That
   variety grows 10 to 15 feet tall.  Together these effects may
   produce a yield multiplier of two to four.  Future research
   may double the yields again by producing higher yielding crop
   varieties.
       The next most important factor is the carbon dioxide
   concentration in the air around your crops.  Resh suggests
   twice to five times the normal amount may be optimal [57, p.297].
   He further states that tomato yields were increased by 20 to
   30% and cucumber yields were increased by up to 40% [57, p.297].
   Carbon dioxide enrichment also produced faster growth rates in
   lettuce and thus permitted an extra crop each year [57, p.297].
   Propane or fuel oil can be burned to provide both carbon dioxide
   and heat.  Dry ice may also suffice.  Since the carbon dioxide
   in the air is the plants only source of carbon, which as we saw
   above amounts to 45% of the plant's dry weight, it is not
   surprising that this factor is so important.  Research in Canada
   has also shown that carbon dioxide enrichment produces a 15 to
   20% increase in plant growth [83, p.7].  Thus we conclude
   that the carbon dioxide multiplier will be in the range of 1.2
   to 2.
       The temperature of the plant and its surroundings are quite
   important to plant growth.  Table 2.1-1 given below was produced
   by J.F. Harrington of the Department of Vegetable Crops at the
   University of California at Davis.  It shows the very significant
   effects of temperature on the germination time of various seeds.
   You can see that the germination time is weeks faster at the
   optimal temperature.  Each crop has its preferred growing
   temperature and that temperature also varies depending upon what
   growth phase the plant is in.  Most plants prefer 75F to 85F for
   optimal growth - and that applies to their roots as well! "Growing
   Greenhouse Vegetables" states that the increase in leaf and flower
   initiation is about 10% for each degree Centigrade increase 
   [83, p.4].
*        Table 2.1-1  Days for Seed to Emerge at Different Temperatures
                      Temperature in degrees Centigrade
   Crop          0     5     10    15    20    25    30    35    40
   Asparagus     -     -    52.8  24.0  14.6  10.3  11.5  19.3  28.4
   Bean,lima     -     -     -    30.5  17.6   6.5   6.7   -     -
   Bean,snap     -     -     -    16.1  11.4   8.1   6.4   6.2   -
   Beet          -    42.0  16.7   9.7   6.2   5.0   4.5   4.6   -
   Cabbage       -     -    14.6   8.7   5.8   4.5   3.5   -     -
   Carrot        -    50.6  17.3  10.1   6.9   6.2   6.0   8.6   -
   Cauliflower   -     -    19.5   9.9   6.2   5.2   4.7   -     -
   Celery        -    41.0  16.0  12.0   7.0   -     -     -     -
   Corn          -     -    21.6  12.4   6.9   4.0   3.7   3.4   -
   Cucumber      -     -     -    12.0   6.2   4.0   3.1   3.0   -
   Eggplant      -     -     -     -    13.1   8.1   5.3   -     -
   Lettuce      49.0  14.9   7.0   3.9   2.6   2.2   2.6   -     -
   Muskmelon     -     -     -     -     8.4   4.0   3.1   -     -
   Okra          -     -     -    27.2  17.4  12.5   6.8   6.4   6.7
   Onion       135.8  30.6  13.4   7.1   4.6   3.6   3.9  12.5   -
   Parsley       -     -    29.0  17.0  14.0  13.0  12.3   -     -
   Parsnip     171.7  56.7  26.6  19.3  13.6  14.9  31.6   -     -
   Pea           -    36.0  13.5   9.4   7.5   6.2   5.9   -     -
   Pepper        -     -     -    25.0  12.5   8.4   7.6   8.8   -
   Radish        -    29.0  11.2   6.3   4.2   3.5   3.0   -     -
   Spinach      62.6  22.5  11.7   6.9   5.7   5.1   6.4   -     -
   Tomato        -     -    42.9  13.6   8.2   5.9   5.9   9.2   -
   Turnip        -     -     5.2   3.0   1.9   1.4   1.1   1.2   -
   Watermelon    -     -     -     -    11.8   4.7   3.6   3.0   -
   Source: J.F.Harrington, Dept of Vegetable Crops, UC Davis,
           Agricultural Extension Leaflet, 1954.
.
    Light itself is also a very important factor.  We assume that
   the grower exposes his crops to sunlight whenever possible even
   though it may be diminished by passing through plastic or tinted
   glass.  Obviously cutting off the light to your crops will reduce
   your yield to zero (unless you are growing mushrooms or bean
   sprouts).  In multi-layered greenhouses artificial light may be
   needed.  In space we may have unlimited sunlight although it may
   require some cleverly placed mirrors to utilize it.  A graph is
   given in [89, p.235] which shows the effect of light level on the
   growth of corn, tomatoes, and collards.  It shows that a reduction
   in the ambient light level to about half of the normal noonday
   level of 10000 foot candles reduces the plant growth by about 20%.
   Further reductions below that amount of light cause a dramatic drop
   off in plant growth.  Plants prefer light of wavelengths in the
   range of 360 - 760 nm (nanometers) [89, p.237].  Plant photosynthesis
   is especially responsive to blue light (around 430 nm) and red
   light (around 660 nm).  Plant germination, flower growth, and
   stem growth are especially responsive to red light (around 660 nm)
   and far red light (around 735 nm) [89, p.237].  Cool white
   flourescent lights provide a light spectrum which covers these
   perferred wavelengths [89, p.237].
       Clearly ample water is critical.  This is not generally a
   problem in greenhouses, but in the fields drought can be devastating.
   Plants can also be drowned in too much water in as little
   as a few hours.  Generally more than 90% by weight of your vegetable
   crop is water [79].  Fruits average about 86% water [79].
       Another very important factor is fertilizer.  In greenhouse
   and hydroponic operations the fertilizer is dissolved in the
   water to create a nutrient solution and then pumped to the plants.
   Clearly if the plants don't get the nutrients they need, they
   will either die or grow sub-optimally.  In either case your
   yield will be less than it could have been.
       Other factors which effect plant growth include:  relative
   humidity, the PH of the nutrient solution, the amount of oxygen
   the plant roots receive, nighttime temperature, number of hours
   of illumination per day, pollination considerations, and believe
   it or not, the sounds your plants "hear".  The impact of each
   of these factors is not easy to pin down, but they are still
   very important.  What happens if your plants are not pollinated?
   Obviously you get no harvest unless you are using selfpollinating
   crops or crops which don't require pollination.
       Crop yields are also effected by plant diseases, pest damage,
   and bad weather.  The latter two problems can be nearly eliminated
   by indoor growing and this is truly a fundamental advantage of
   greenhouse or hydroponically grown crops.  The losses in field crops
   due to insects, birds, mammals, weeds, and pathogens is about 33%
   [90, p.25] and rises to 40% without pesticides [90, p.25].  Even
   greenhouse growers must fight off pests.  In space or at a lunar
   base we don't anticipate any pest problems because we will simply
   insure that none is taken with us.  Bad weather won't stop
   either of course, but unless your buildings are damaged or destroyed,
   the only impact on you will be higher bills for heating or
   cooling.  Plant diseases are another story.  This is one area where
   indoor crops can be devastated.  In hydroponic operations, the
   same nutrient solution is used to nurish bed after bed of crops.
   If that water contains some kind of water-borne disease, you can
   lose a whole crop.  In nearly all indoor operations, the growing
   medium is sterilized after each crop to try to eliminate carryover
   of diseases from one crop to the next.  In many places around the
   world, human waste is used to fertilize crops.  This often leads
   to dysentery in the consumers.  Clearly this problem is completely
   eliminated through the use of nutrient solutions in hydroponic
   growing facilities.
       There are probably many more factors of which I am unaware, but
   this list should give you an idea of how yields can be improved.
       Now let us give a grand summary of these factors.
*      Factor             Yield multiplier
       ------               ----------
       Plant density           4-16
       Crops per year          2-8
       Crop variety            2-4
       Carbon dioxide level    1-2
       Fertilizer              1-2
       Light level             1-2
       Pollination             1-2
       Temperature             1-2
       Water                   1-2
       Others                  1-2 each
.
       If you multiply all these factors together, you can easily
   exceed 100 times the field yield.
   2.2  Analysis of vegetables
       The following table [2.2-1] of vegetable data was assembled
   from a variety of sources which are listed at the end of the table.
   These data form the basis from which we project our results.
   Perhaps a few words are in order about how these data were
   selected.  The pricing information was collected over a period
   of about three years (1989-1991).  It was collected only from
   large stores in my geographical region which is eastern
   Pennsylvania, USA.  The prices represent the lowest common price
   for each product.  The prices shown are generally one half to one
   third of the highest price recorded over the period.
       The germination data were obtained from references 75 and 76.
   Where the data were not broken down by variety, the data were simply
   duplicated for each variety as in onions, peppers, and squash.
       The time to maturity data were obtained from references 76
   and 78.  Here the absolute minimum was not selected, but rather
   the lowest common time.  We felt that the absolute fastest growing
   crop  might not have the best taste, the factor which we consider
   most important.  We did select a short time however, because we want
   to increase  yields which is done by using fast growing crops.
       The plant spacing was obtained from references 77 and 78.
   The spacing was changed for those crops which can be trained to
   grow vertically such as cucumbers, tomatoes, and squash.
       The yield information came primarily from Gurney's spring
   1990 catalog [Ref 78].  Again, where the data were not broken down
   by variety, they were simply duplicted. One major problem with
   this data is the following.  Many crops such as tomatoes, squash,
   cantaloupes, and (snap) pole beans take a long time to grow to
   maturity and then they produce continuously until they are killed
   by frost.  In the case of indoor crops there will be no frost so
   what then will be their yield?  And also how many crops will you
   get per year?
       Crop heights and crop consumption information came from
   references 80 and 81 which are "Fruit and Vegetable Facts & Pointers"
   and "Supply Guide" both published by United Fresh Fruit and
   Vegetable Association of Alexandria Va.  It is clear that if we
   have no meat in space, then we will have vegetarian diets.  This
   will obviously change our consumption figures drastically.  We
   anticipate that people will desire as much variety as possible
   so that even those crops which presently show low consumption
   figures will become popular.
*  Table 2.2-1     Data for Selected Common Vegetables
   Vegetable       price germ grow total spc yield  harv  ht  #/p
                   cents days days days inch  lbs  index  ft  /yr
   Artichoke         67    7   365  372  60   100   0.05   4  0.4
   Asparagus        149   10  1000 1010  30    30   0.20   4  0.5
   Beans,-snap-bush  69    7    50   57   4    48   0.20   2  1.1
   Beans,-snap-pole  69    7    60   67  12   128   0.20  10  0.0
   Beans,-sprouts   133    6     6   12   1    10   1.00   1  0.0
   Beets            -20    5    55   60   4   100   1.00   1  0.1
   Bok-Choy          89    4    45   49   8   150   0.67   2  0.5
   Broccoli         -79    4    60   64  18   100   0.33   2  3.2
   Brussel-sprouts  172    4    80   84  18    60   0.50   2  0.1
   Cabbage,-green    29    4    65   69  12   150   0.67   1  5.4
   Cabbage,-red      39    4    70   74  12   200   0.67   1  0.0
   Carrots           35    6    60   66   2    75   0.80   1  8.0
   Cauliflower      -99    5    55   60  15   -80   0.33   2  2.5
   Celery           -69    7    90   97   6  -200   0.75   2  7.2
   Collards          69    5    65   70  12   100   0.67   3  0.0
   Corn, sweet      -15    4    60   64   8  -150   0.05  12  7.4
   Cucumbers         33    3    55   58  18   400   0.20   2  4.4
   Eggplant          59    6    75   81  18  -167   0.33   4  0.6
   Escarole          59    5    45   50   6   100   0.67   1  0.4
   Kale              59    6    55   61   8    75   0.67   2  0.0
   Leeks            149   19    80   99   4    75   0.75   2  0.0
   Lettuce,-Iceberg  69    3    70   73  10  -120   0.67   1 21.2
   Lettuce,-leaf     99    3    45   48   6   100   0.67   1  1.5
   Lettuce,-Romaine  59    3    80   83   6   100   0.67   1  1.4
   Onions,-green    133    6    70   76   2    50   0.80   1  0.8
   Onions,-red       59    6   105  111   4   100   0.67   1  0.0
   Onions,-spanish   49    6   105  111   4   100   0.67   1  0.0
   Onions,-white     59    6   100  106   4   100   0.67   1 12.4
   Onions,-yellow    39    6   100  106   4   100   0.67   1  0.0
   Parsnips          99   14   100  114   4   100   1.00   1  0.0
   Peas             369    6    65   71   4    64   0.25   2  0.1
   Peppers,Cubannel  89    8    65   73  12  -800   0.25   3  0.0
   Peppers,-green    59    8    60   68  12  -600   0.25   3  3.4
   Peppers,-hot      89    8    78   86  12 -1000   0.25   2  0.0
   Peppers,-orange  129    8    65   73  12  -600   0.25   3  0.0
   Peppers,-yellow  129    8    65   73  12  -600   0.25   3  0.0
   Potatoes,-Idaho   28    9    90   99  10   240   0.25   2 47.2
   Potatoes,-red     28    9   100  109  10   240   0.25   2  0.0
   Potatoes,-sweet   49    7   100  107  12   240   0.50   2  4.8
   Radishes          49    3    23   26   2    20   0.67   1  1.0
   Snow Peas        169    6    60   66   4    64   0.25   2  0.0
   Spinach           79    5    45   50   4    10   0.67   1  0.8
   Squash,-acorn     49    4    85   89  18  -667   0.50   8  0.0
   Squash,butternut  39    4    85   89  18  -667   0.50   8  0.0
   Squash,spaghetti  39    4    85   89  18  -667   0.50   8  0.0
   Squash,-green     69    4    50   54  18 -2000   0.50   8  0.8
   Squash,-yellow    69    4    50   54  18 -2000   0.50   8  0.0
   Squash,-zucchini  69    4    50   54  18 -2000   0.50   8  0.0
   Tomatoes,-cherry 139    6    55   61  18   500   0.50   3  0.8
   Tomatoes,regular  49    6    90   96  18  1000   0.50  10 15.6
   Turnips           29    2    45   47   4   100   1.00   2  0.3
   Column   Sources:
   2,5,8    Author
   3        Ref 75 and Ref 76
   4        Ref 76 and Ref 78
   6        Ref 77 and Ref 78
   7        Ref 78 and Author
   9        Ref 80 and Author
   10       Ref 81
   Column   Notes:
   2        This is a retail price in cents per pound.
            A negative price means the price is per piece.
   3        The number of days for the seed to germinate.
   4        The number of days for the crop to mature.
   6        The spacing between plants in inches.
   7        Yield is for a single 100 foot row of plants.
            A negative yield means the yield is a piece count.
   8        This is fraction of the plant which is edible, also
            called the harvest yield. This is basically a SWAG.
   9        Height of plant in feet.
   10       US consumption in pounds per person per year.
            Where consumption is 0, that means either that there
            were no data or that it was very small.  In some cases
            such as potatoes and onions the data were not broken
            down by variety and thus one variety has all of it.
.
       These data were read in by one of my programs and used to
   calculate the data presented in table 2.2-2.  These data are my
   projections of expected yields and income from the various crops
   if they were grown in greenhouses or hydroponically.
       This table shows vividly the vast potential of
   greenhouse or hydroponically grown crops.  The second column shows
   the number of plants per acre in thousands.  Remembering that one
   acre has 43,560 square feet, it can be seen that "44" means one plant
   per square foot and "174" means 4 plants per square foot and so on.
   Clearly the very high density crops are radishes, carrots, green
   onions, and highest of all - bean sprouts.  The number in this
   column is for each crop.
       The third column shows the expected harvest in tons per acre
   per crop.  This was calculated by scaling up the expected harvest
   of 100 feet of each crop (table 2.2-1 column 7) to a whole acre.
   It was then divided by 2000 pounds per ton to give the answer.
       The fourth column is the retail value of each crop in thousands
   of dollars.  This is basically the product of the yield in pounds
   times the value per pound.  The fifth column is the number of
   crops per year.  This was calculated by dividing 365 by the sum
   of the germination time and the time to maturity.  The sixth column
   is the yield per acre per year which is simply the product of the
   yield per crop and the number of crops per year.  The seventh column
   is the growers share of the total retail value of the crop.  It
   represents the growers "gross" income per acre per year for each
   crop.  Clearly the percent of retail that the grower receives will
   vary from crop to crop, but we have used 30% throughout.  Reference
   80 gives figures varying from 34% to 37% for the growers share, but
   those figures are from the early 1970's.
       The last column shows the number of grams of edible food
   product which is grown per square meter per day.  This is the same
   data as in column six, but in different units.  We give this data
   because it is of special interest in space grown crops.  From it
   you can estimate the growing area required to support the crew of
   your spaceship.
*  Table 2.2-2
   Projected Yields from Hydroponic Crops at Minimum Spacing
   Vegetable          P/A  T/A/C   $/C  C/YR Y/A/YR  $/A/YR  G/D
                     1000s        1000s               1000s
   Artichoke            2    4.4     6   1.0    4.3     2     3
   Asparagus            7    2.6     8   0.4    0.9     1     1
   Beans,-snap-bush   392   31.4    43   6.4  200.8    83   123
   Beans,-snap-pole    44   27.9    38   5.4  151.9    63    93
   Beans,-sprouts    6273   26.1    70  30.4  795.0   634   488
   Beets              392   65.3   105   6.1  397.5   191   244
   Bok-Choy            98   49.0    87   7.4  365.0   195   224
   Broccoli            19   14.5    31   5.7   82.8    52    51
   Brussel-sprouts     19    8.7    30   4.3   37.9    39    23
   Cabbage,-green      44   32.7    19   5.3  172.8    30   106
   Cabbage,-red        44   43.6    34   4.9  214.9    50   132
   Carrots           1568   98.0    69   5.5  542.0   114   333
   Cauliflower         28   34.8    28   6.1  212.0    50   130
   Celery             174  130.7   120   3.8  491.7   136   302
   Collards            44   21.8    30   5.2  113.6    47    70
   Corn, sweet         98   12.3    15   5.7   69.9    25    43
   Cucumbers           19   58.1    38   6.3  365.5    72   224
   Eggplant            19   24.2    29   4.5  109.3    39    67
   Escarole           174   43.6    51   7.3  318.0   113   195
   Kale                98   24.5    29   6.0  146.6    52    90
   Leeks              392   49.0   146   3.7  180.7   162   111
   Lettuce,-Iceberg    63   31.4    43   5.0  156.8    65    96
   Lettuce,-leaf      174   43.6    86   7.6  331.2   197   203
   Lettuce,-Romaine   174   43.6    51   4.4  191.6    68   118
   Onions,-green     1568   65.3   174   4.8  313.8   250   193
   Onions,-red        392   65.3    77   3.3  214.9    76   132
   Onions,-spanish    392   65.3    64   3.3  214.9    63   132
   Onions,-white      392   65.3    77   3.4  225.0    80   138
   Onions,-yellow     392   65.3    51   3.4  225.0    53   138
   Parsnips           392   65.3   129   3.2  209.2   124   128
   Peas               392   41.8   309   5.1  215.0   476   132
   Peppers,-Cubannel   44   32.7    58   5.0  163.4    87   100
   Peppers,-green      44   49.0    58   5.4  263.0    93   162
   Peppers,-hot        44   27.2    48   4.2  115.5    62    71
   Peppers,-orange     44   57.2   148   5.0  285.9   221   176
   Peppers,-yellow     44   57.2   148   5.0  285.9   221   176
   Potatoes,-Idaho     63   62.7    35   3.7  231.3    39   142
   Potatoes,-red       63   62.7    35   3.3  210.0    35   129
   Potatoes,-sweet     44   52.3    51   3.4  178.3    52   110
   Radishes          1568   26.1    26  14.0  366.9   108   225
   Snow Peas          392   41.8   141   5.5  231.3   235   142
   Spinach            392    6.5    10   7.3   47.7    23    29
   Squash,-acorn       19  193.7   190   4.1  794.4   234   488
   Squash,-butternut   19   96.8    76   4.1  397.2    93   244
   Squash,-spaghetti   19  193.7   151   4.1  794.4   186   488
   Squash,-green       19  145.2   200   6.8  981.4   406   603
   Squash,-yellow      19  145.2   200   6.8  981.4   406   603
   Squash,-zucchini    19  145.2   200   6.8  981.4   406   603
   Tomatoes,-cherry    19   72.6   202   6.0  434.4   362   267
   Tomatoes,-regular   19  145.2   142   3.8  552.1   162   339
   Turnips            392   65.3    38   7.8  507.4    88   312
   Column  Notes:
   2       P/A       plants per acre  (in 1000s)
   3       T/A/C     tons per acre per crop
   4       $/A/C     retail dollars per acre per crop (in 1000s)
   5       C/YR      number of crops per year
   6       Y/A/YR    total yield per acre per year in tons
   7       $/A/YR    farmer's gross share = 30%       (in 1000s)
   8       G/D       edible plant growth in grams/sq meter/day
.
   2.3  Are these numbers for real?
       The reader is probably wondering if these projections are
   really possible.  The answer is that they definitely are!  Look
   at table 2.3-1.  This table compares the normal field yields of
   some selected crops (those for which I could find the data) with
   the projected greenhouse or hydroponic yields and also with actual
   yields of several greenhouse or hydroponic operations for which
   I was able to find data.  Most of the "actual" data comes from
   the Abu Dhabi operation as reported by Resh [57, p.219-222].
       The field yields come from references 80 and 82.  These yields
   are significantly lower than the yields given by Gurney [78, p.4]. A
   small backyard garden receives more TLC than the average field crop.
   The projected yields are from table 2.2-2 column 3.  The yield
   of 20 tons per acre of bush beans came from reference 80 and
   appeared in October 1976 in the report NRP 20020 of the
   Agricultural Research Service.
       Notice that some of the actual yields are much higher than
   the projected yields.  Resh gives a yield of 300 tons per acre
   per year for a tomato crop [57, p.29], but he states that the
   yield per plant was 18 to 20 pounds [57, p.28].  Perhaps if they
   used the variety offered by Gurney [78, p.16] which yields 50
   pounds per plant, they could do twice as well.
       The leaf lettuce result was the Whittaker Corp in Somis, CA.
   [57, p.150].  The head lettuce result was from Hidroponias
   Venezolanes, S.A., Caracus, Venezuela [57, p.248-9].
*        Tabel 2.3-1  Comparison of Selected Vegetable Yields
                Hydroponic Yields
   Vegetable        Field  ---------------------------
                    Yield   Proj  Actual  C/YR  total   source
                    T/A/C  T/A/C  T/A/C    #    T/A/YR
   Artichoke         3.5     4.4
   Asparagus         1.2     2.6
   Beans,-bush       2.4    31.4  20.0 *  6.4 =  128  [80, UFFVA]
   Beets             6.25   65.3
   Broccoli          3.75   14.5  13.0 *  3.0 =   39  Abu Dhabi [57]
   Brussel-sprouts   6.0     8.7
   Cabbage          10.8    43.6  41.4 *  5.0 =  207  Abu Dhabi [57]
   Carrots           6.25   98.0
   Cauliflower       9.0    34.8
   Celery           25.0   130.7
   Collards          5.0    21.8
   Corn,sweet        3.0    12.3
   Cucumbers         5.4    58.1  65.7 *  6.3 =  414  Abu Dhabi [57]
   Eggplants         7.5    24.2  42.7 *  4.5 =  192  Abu Dhabi [57]
   Escarole          7.0    43.6
   Lettuce,iceburg  10.8    31.4  28.5 *  5.0 =  142  [57, p.248]
   Lettuce,-leaf     7.5    43.6 101.2 *  8.0 =  809  [57, p.150]
   Onions,-green    48.0    65.3
   Onions,-white    35.0    65.3
   Parsnips          4.0    65.3
   Peas              2.4    41.8
   Peppers,-green    9.6    49.0
   Potatoes,-idaho  13.5    62.7
   Potatoes,-sweet   7.0    52.3
   Squash,-summer    4.0   145.2
   Squash,-winter    8.75  193.7
   Spinach           3.6     6.5
   Tomatoes,cherry   4.0    72.6
   Tomatoes,regular 10.8   145.2 150.0 *  2.0 =  300  [57, p.29]
   Turnips          10.0    65.3  45.4 *  7.8 =  354  Abu Dhabi [57]
   Column   Notes
   1        Crop
   2        Field yield in tons per acre per crop
   3        Projected yield in tons per acre per crop
   4        Actual yield in tons per acre per crop
   5        Number of crops per year
   6        Total yield in tons per acre per year
   7        Source
.
   2.4  Analysis of fruits
       Comparitively little work has been done on greenhouse or
   hydroponically grown fruits.  The only fruit mentioned by Resh
   is strawberries.  Two examples were given; one in the Canary
   Islands where strawberries are being grown in columns [57, p.278]
   and the other in Catania, Italy where strawberries are being
   grown in sacks which are hung from overhead supports 
   [57, p.279-284].
       The primary reason for this is the simple fact that most
   fruits grow on trees and those trees are fairly tall.  This makes
   it quite expensive to grow them indoors.
       There are several fruits which could be grown indoors
   including:  cantaloupes, honeydews, grapes, kiwis, pineapples,
   strawberries, and possibly raspberries.  The first four are vine
   crops whereas the latter three are individual plants as opposed
   to trees.  Unfortunately raspberries do not lend themselves well
   to greenhouse operations because of their thorns and heavy labor
   requirements.  Too bad, they are one of my favorites.
       The crew of a spaceship will want fruit in as wide a variety
   as possible.   They will desire it not only for its taste but
   also to fight the boredom of constant vegetarian meals.  Gurney's
   offers some dwarf fruit trees which are one half to one third of
   the height of ordinary fruit trees [78, p.36-41].  Of course the
   yield is one half to one third as well.
       Significant additional research needs to be done to determine
   the optimal growing conditions for each of these fruits and to
   discover which ones we could economically raise in space.
       The following table [2.4-1] shows the nutrient value of some
   of the more common fruits.
*  Table 2.4-1       Nutrient Value of Fruits
                (All quantities are 1/2 pound)
   Fruit             water  E  Prot Carb  Na   K    P   Ca   Fe
                 Cost  %   cal  gm   gm   mg   mg   mg  mg   mg
   Apples         79   84  131   0   35    0  261   16  16  0.3
   Apricot        79   86  107   2   26    2  672   43  32  1.3
   Bananas        37   74  209   2   54    2  897   46  14  0.8
   Cantaloupe   -169   90   81   2   19   20  701   38  25  0.5
   Cherry         99   81  167   3   37    0  507   43  33  1.0
   Coconuts      -57   47  806   5   35   45  806  257  30  5.5
   Grapes        129   81  159   0   41    5  422   32  27  0.5
   Grapefruit     40   91   76   2   19    0  316   19  26  0.2
   Honeydew       69   90   79   2   21   23  615   23  14  0.2
   Kiwi          -24   83  134   3   33   12  752   90  60  0.9
   Lemon         -25   91   56   1    5    1   74    8  14  0.3
   Lime(juice)   -25   90   60   1   20    2  247   16  20  0.1
   Oranges       -25   87  104   2   26    0  410   31  90  0.2
   Peaches        99   88   91   3   26    0  446   26  10  0.3
   Pears(Anjou)   79   84  136   1   34    0  283   25  25  0.6
   Pears(Bosc)    89   84  137   2   34    0  283   26  26  0.6
   Pineapple    -177   87  110   1   28    3  256   16  16  0.9
   Plums         129   85  120   3   31    0  392   24  10  0.3
   Raspberries   400   87  111   2   26    0  345   28  50  1.3
   Strawberries  169   92   68   2   15    2  376   43  32  0.9
   Tangerines    -33   88   94   3   24    3  356   22  32  0.3
   Watermelon     39   92   73   1   16    5  263   20  18  0.4
   Fruits have no cholesterol and less than 1 gram of fat.
   Sources:  Column 2 (Author's research) retail cost in cents
       per pound; A negative cost means price per piece.
       Remainder of table from:
       [79] "Nutritive Value of Foods", by S.E. Gebhardt,
       R.H. Mattews, USDA Home and Garden Bulletin #72,
       USGPO, 1981.
   Notes:    Na - Sodium        E  - energy in calories
             K  - Potassium     gm - grams
             P  - Phosphorus    mg - milligrams
             Ca - Calcium       %  - percent by weight of water
             Fe - Iron          Prot - protein
             Carb - carbohydrate
.
   2.5  Nutrient value of vegetables
       Table 2.5-1 shows the nutrient value of some of the more
   common vegetables.  The data were extracted from "Nutrient Value of
   Foods" by S.E. Gebhardt and R.H. Mattews, USDA Home and Garden
   Bulletin #72, 1981.  All data were scaled up to 1/2 pound servings.
*  Table 2.5-1       Nutrient Value of Vegetables
                   (All quantities are 1/2 pound)
   Vegetable          water  E  Prot Carb   Na  K    P    Ca   Fe
                   Cost %   cal  gm   gm    mg  mg   mg   mg   mg
   Artichoke        67  87  104   6   23   149  597  136   89  3.0
   Asparagus       149  92   57   8   11     8  703  140   53  1.5
   Beans,snap-bush  69  89   82   4   18     7  679   89  105  2.9
   Beans,sprouts   133  90   65   7   13    13  338  122   31  2.0
   Beets           -20  91   68   7   16   111  708   70   25  1.4
   Bok-choy         89  96   27   4    4    77  842   65  211  2.4
   Broccoli        -79  91   60   6   12    62  737  150  108  2.0
   Brussel sprouts 172  87   88   6   19    48  718  127   82  2.8
   Cabbage,-green   29  93   49   3   13    42  557   52  107  1.3
   Cabbage,-red     39  92   65   3   13    26  467   94  117  1.0
   Carrots          35  88   94   3   22    79  734  101   60  1.3
   Cauliflower     -99  92   57   5   11    34  805  104   66  1.4
   Celery          -69  95   28   0    6   198  646   57   79  1.1
   Collards         69  96   30   2    6    43  211   23  177  1.0
   Corn, sweet     -15  70  250   9   56    38  566  233    6  1.5
   Cucumbers        33  96   40   0    8     8  340   40   32  0.8
   Eggplant         59  92   59   2   14     7  562   50   14  0.7
   Endive           59  94   45   5    9    50  712   64  118  1.8
   Kale             59  91   70   3   12    52  516   63  164  2.1
   Leeks           149  83  140   4   31    44  410   79  131  4.8
   Lettuce,iceberg  69  96   29   2    5    21  359   45   43  1.1
   Lettuce,romaine  59  96   40   4    8    20  599   57  154  3.2
   Mushrooms       109  92   65   3   10    10  839  237   13  2.9
   Onions,-green   133  92   76   8   15     8  582   76  136  4.5
   Onions,-white    59  91   78   3   17     4  352   65   57  0.9
   Parsnips         99  78  182   3   44    23  833  157   84  1.3
   Peas            369  89   92   7   16     9  544  125   95  4.5
   Peppers,green    59  93   61   3   12     6  441   49   12  2.8
   Peppers,hot      89  88  101   5   20    15  771  106   40  2.5
   Potatoes         28  71  247   6   57    18  948  129   22  3.0
   Potatoes,sweet   49  73  229   4   56    22  790  125   64  1.0
   Radishes         49  95   63   0   13    50  529   38   50  1.3
   Snow peas       169  89   92   7   16     9  544  125   95  4.5
   Spinach          79  92   41   8    8   177 1266  111  223  6.2
   Squash,-winter   49  89   89   2   20     2  991   45   32  0.8
   Squash,-summer   69  94   44   3   10     3  436   88   62  0.8
   Tomatoes         49  94   46   2    9    18  470   52   17  1.1
   Turnips          29  94   44   1   12   113  307   44   49  0.4
   Vegetables have no cholesterol and less than 1 gram of fat.
   Sources:  Column 2 (Author's research) retail cost in cents
       per pound; A negative cost means price per piece.
       Remainder of table from:
       [79] "Nutritive Value of Foods", by S.E. Gebhardt,
       R.H. Mattews, USDA Home and Garden Bulletin #72,
       USGPO, 1981.
   Notes:    Na - Sodium        E  - energy in calories
             K  - Potassium     gm - grams
             P  - Phosphorus    mg - milligrams
             Ca - Calcium       %  - percent by weight of water
             Fe - Iron          Prot - protein
             Carb - carbohydrate
.
   2.6  Financial considerations
   According to the "Greenhouse Vegetable Guide" published by
   Texas A&M [Ref 120], the cost of building a greenhouse varied from
   $1.90 per square foot to over $30 per square foot with the weighted
   average at $6 per square foot [120, p.105].  That works out to
   $261,360 per acre - obviously beyond the means of the average
   person - and that doesn't include the cost of the land.  Including
   other necessary equipment, the total average cost was $6.52 per
   square foot or $284,011 per acre [120, p.106].  In addition the
   average yearly production costs (for growing tomatoes) was about
   $3.92 per square foot or $170,755 per acre [120, p.107].  About half
   ($1.95 psf) of this cost is interest and depreciation.   The cost
   of labor is included in the remainder and 25% of that is assumed
   to be paid to the owner/operator for his labor.  On the
   other hand, total revenue was $4.77 per square foot or $207,781 per
   acre [120, p.108].  This yields a net profit of $0.85 per square
   foot or $37,026 per acre.  Not counting interest and depreciation,
   the profit would be $2.80 per square foot or about $122,000 per
   acre.   This analysis is based on a yield of 20 pounds of top grade
   tomatoes (at $0.80 per pound) and 7 pounds of salable culls (at
   $0.40 per pound) or 27 pounds per plant ($18.80 per plant) - which is
   only about half of what they could be getting according to Gurney's
   [78, p.16].
       Another detailed cost outline was given in "Florida Greenhouse
   Vegetable Production Handbook", published by the University of
   Florida's cooperative extension service [Ref 128].  Their very
   detailed cost breakdown gives a total construction cost of about
   $298,000 per acre or $6.84 per square foot [128, p.93]. Further (five
   year) fixed costs of $47,800 per acre are given.  Variable costs were
   estimated to be $122,460 per acre [128, p.94].  The gross revenue
   was estimated to be $179,150 per acre based upon 4 square feet per
   plant, 22 pounds of tomatoes per plant, and a price of $0.75 per
   pound or $16.50 per plant [128, p.97].  That works out to $4.11 per
   square foot.  The expected profit was $67,295 per acre or $1.54 per
   square foot, not counting interest or depreciation [128, p.97].
       The Ontario Ministry of Agriculture and Food [83] gives some
   interesting data on Canadian greenhouse production.  They state that
   450 acres of Ontario greenhouses had a grower value of $45 - $50
   million in 1986 [83, p.3].  That works out to at least $100,000 per
   acre or $2.29 per square foot.
       In summary we have:
*      Area       Profit (psf)      Profit per acre
       Florida      $1.54        $67,295
       Ontario      $2.29       $100,000
       Texas        $2.80       $122,000
.
   2.7  Financial summary
*      Cost will be:  $300,000 per acre for construction
       Years 1 - 7 :   $50,000 per acre profit, $50,000 loan repayment
       Years 8 +   :  $100,000 per acre profit.
.
       That is a 16.67% return on investment for the first 7 years and
   a 33.3% return thereafter.  Most people would consider that a good
   investment.  We believe that $300,000 per acre for construction is
   very high.  If the cost could be brought down to $100,000 per acre,
   then the facility could be doubled every two years with no 
   additional investment.
       This estimate is for tomatoes, but we can't all grow tomatoes.
   Other crops offer as good or better possible returns (see table
   2.2-2).
   2.8  Political summary
       1. The yields of hydroponic crops can be 100 times as high as
   that of field grown crops.
       2. Hydroponic or greenhouse production of vegetable crops will
   provide a more reliable source of food due to its year round growing
   season and lower susceptability to bad weather and pest damage.
       3. Low quality and therefore low cost land can be used for
   hydroponics since the soil is not used. Since the government owns
   lots of land, the land cost should be almost nothing.
       4. The construction of the facilities will create jobs in the
   construction industry.
       5. Facilities could be constructed in center cities.  That
   would save on transportation costs between the growing facilities
   and the market.  Unemployed people could be hired to pick and pack
   the harvest.