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.
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