the

mineral


nutrients.
Plants

that


are


not


traditionally

grown


in


a

climate

would

be

possible

to


grow

using


a

controlled


environment
system
like


hydroponics.


During


World

War


II

produce

was


grown


with


hydroponics


on

the


barren


Pacific
Islands.

According


to


a

1938


Times


magazine


article,


this

was


one

of


the


first


times


that


commercial


use

of
hydroponics

was


used

on

such

a

large


scale


to


feed


people.


This


group

of


islands

was


used

as

a

refueling
stop

for


Pan

-

Am

Airways


and

the


food


was


used

to


feed


the


staff


and

crew.


This


means


that


salad


greens
could

possibly

be

grown


in


Antarctica


or


even

the


Mojave


Desert.


NASA

has

also


looked


to


utilize

hydroponics
in

the


space

program.


Ray


Wheeler,


plant


physiologist


at


Kennedy


Space


Center’s


Space


Life

Science

Lab,
believes
that


hydroponics


will


create


advances


within

space

travel.


He


terms

this

as

“a


life


support


system

with
the

biological


component


of


growing


plants—called


a

bio

-

regenerative

life


support


system.


It

has

several
benefits

for


NASA.”


These


Scientists


are


researching


how


different


amounts


of


light,


temperature


and

carbon
dioxide,

along


with


plant


species


can

be

grown


and

cultivated


on

planets


like


Mars.
Disadvantages
The

hydroponic


conditions


(presence


of


fertilizer


and

high


humidity)

create


an

environment


that


stimulates
salmonella

growth.


Other


disadvantages


include

pathogen

attacks

such

as

damp

-

off


due

to


Verticillium


wilt
caused

by

the


high


moisture


levels

associated


with


hydroponics


and

over

-

watering


of


soil


based


plants.


Also,
many

hydroponic


plants

require

different


fertilizers


and

containment


systems.



The


main

disadvantage


is


the
required
replacement


of


a

percentage


of


the


water


on

regular

bases.



The


reason

being


is


that


the


nutrients
placed

in


the


water


to


fertilize

the


plants

gets


used

over


a

period


of


time


and

when


it

does,


it

leaved


harmful
chemical

salts

in


its

place


which

are


harmful


to


the


plants.



Therefore,


a

regular

run

-

off


of


water


is


necessary
to

eliminate


the


salts.



This


in


turn


causes

a

problem

with


the


EPA


(Environmental


Protection


Agency).



We

all
know

who


they


are


and

they


require

strict


disposal


of


the


water


run

-

off


from

hydroponic


systems

in


order


to
protect
the


environment


and

the


aquifer

from

pollution.
Nutrient

solutions
Numerous
'recipes'


for


hydroponic


solutions


are


available.


Many


use

different


combinations


of


chemicals


to
reach

similar


total


final


compositions.


Commonly


used

chemicals


for


the


macronutrients

include

potassium
nitrate,
calcium


nitrate,

potassium

phosphate,


and

magnesium

sulfate.


Various


micronutrients


are


typically
added

to


hydroponic


solutions


to


supply


essential


elements;


among

them

are


Fe

(iron),


Mn


(manganese),


Cu
(copper),

Zn

(zinc),


B

(boron),


Cl


(chlorine),


and

Ni


(nickel).


Chelating


agents


are


sometimes


used

to


keep

Fe
soluble.

Many


variations


of


the


nutrient


solutions


used

by

Arnon

and

Hoagland


(see


above)

have

been


styled
'modified

Hoagland


solutions'


and

are


widely


used.


Variation


of


different


mixes

throughout


the


plant


life


cycle,
further

optimizes


its

nutritional


value.
Plants

will


change


the


composition


of


the


nutrient


solutions


upon


contact


by

depleting

specific


nutrients


more
rapidly

than


others,

removing

water


from

the


solution,


and

altering


the


pH


by

excretion

of


either


acidity


or
alkalinity.

Care

is


required

not


to


allow


salt

concentrations


to


become

too


high,


nutrients


to


become

too
depleted,
or


pH


to


wander


far


from

the


desired


value.
Commercial
The

largest


commercial


hydroponics


facility


in


the


world


is


Eurofresh


Farms


in


Willcox,


Arizona,


which

sold