Plant Nutrition in Soilless Culture

 Optimal nutrition is a critical component

of any successful plant production system.
 While plants display an amazing tolerance
and will grow under a wide variety of
nutrient conditions, careful attention to a
plant’s specific requirements is necessary if
that plant’s maximum potential is to be
achieved.
 In SC systems, where intensive production
and maximum yields are the targeted goals,
it is crucial that essential nutrients are not
limiting to the crop.
 Plants need 17 elements - normal growth.
 9 elements - large amounts – macronutrients
 C, H, O – from air and water
 Primary nutrients (N, P, K) - supplemented as
fertilizers
 Secondary nutrients (Ca, Mg, S) - typically readily
available and in adequate supply
 8 other elements - smaller amounts - micronutrients,
or trace elements (TE)
 Eg. Fe, Zn, Mo, Mn, B, Cu, Co and Cl -from soil

All 17 elements - essential elements for plant growth.

Except CHO, all are from soil or in the case of
hydroponics from nutrient solutions or aggregate media
 the soilless cultivation grower must
supply all of these elements to the
plants through the nutrient solution.
 Nutrient solution need to be tailored
to meet the specific demands of your
plants.
 Main objective: to provide enough
nutrient to root zone to allow plant
tissue concentration to remain above
critical concentration but below the
toxic zone.
 At both extremes reduced growth
rate/yield
It is important to note that the
“adequate zone” is fairly wide.
This is true for the macronutrients,
while the window of tolerance for many
of the micronutrients is quite narrow.
The upper end of the adequate zone
represents luxury consumption, that is
the plant tissue continues to accumulate
the nutrient with no further increase in
yield resulting.
Therefore, being at the high end of
the adequate zone (near the toxic
zone) generally indicates that
nutrient concentrations supplied to
the plants could be lowered
considerably without negatively
affecting the plants.
When considering a reduction in a
macronutrient such as nitrogen, this
could mean significant savings in
fertilizer costs as well as decreased
concern over leaching of nitrates to
ground water
Use of nutrient solutions in place
of soil allows the grower a high
degree of control over crop
nutrition.
The initial decision that must be
made by the grower involves the
selection of a nutrient solution
formula from a long list of available
recommendations.
 “No
 As Hoagland and Arnon (1950) stated,
one nutrient solution is superior to all
other solutions…

 Often thought that some remarkable new

combination of salts has been devised and
that the prime requisite for growing crops in
solutions is to use this formula. The fact is,
there is no one composition of a nutrient
solution which is always superior to every
other composition”.
 Although over five decades have passed
since the above statement was made, it is
still very true.
 Several factors which should influence of
choice of nutrient solution -
1.the crop being grown,
2.the growth phase of the crop,
3.the climatic conditions (heat, light, relative
humidity) in the growing area,
4.and the growing system being utilized.
 Even after the proper nutrient
solution has been selected, the
successful grower must consider
several factors for the proper
management of any nutrient
solution.
 These factors - pH, cation:anion
balance, nutrient interactions,
and nutrient mobility
 Critical factor to consider when determining the
availability of nutrients in the solution for
uptake by the plant roots.

 (Lucas and Davis, 1961)-Figure: the uptake of

several nutrients is inhibited under either
strongly acid or strongly alkaline conditions.

 Figure actually refers to nutrients in organic soils,

Correctly assume that plant roots would be even
more sensitive to pH changes in an un-buffered
hydroponic nutrient solution.
 Therefore, if iron, manganese, or
boron deficiency symptoms begin to
occur, check the solution pH before
adding more nutrients - may have a
problem with nutrient availability
rather than with actual low nutrient
supply.
 pH of 5.5 to 6.5
 however, plant roots can over time,
effectively change the pH of the
solution surrounding them by
releasing either H+ or HCO3
(bicarbonate) ions into the medium
in an attempt to maintain their
internal balance of cations
(positively charged ions) to anions
(negatively charged ions).
 It is due to the plant’s need to
maintain its electrical neutrality
that a significant amount of pH
control can be achieved by simply
selecting a certain ratio of nitrate
(NO3) to ammonium (NH4+) ions
when initially formulating the
nutrient solution.
When a NO3- ion is taken up by a
root the root releases a HCO3- ion
into the medium causing a
gradual increase in solution pH.
when an NH4+ ion is absorbed by
the root, a H+ is released, causing
an acidification of the
surrounding medium.
 A NO3-:NH4+ ratio of 9:1 maintained a fairly
stable pH, while rations greater than 9:1
increased pH and less than 9:1 decreased
pH.

 While this may be very helpful information,

before deciding on the correct NO3-:NH4+
ratio for your crop production system, it is
important to consider that choice of N source
also affects cation:anion balance and nutrient
interactions
 Plants not only maintain a cation:anion
balance, but also strive to maintain a total
sum of cations within their tissues
regardless of variations in the
concentrations of individual cations in the
nutrient solution.
 supply of one cation :  uptake of one or
more of the other cations.
 Relationship: cation antagonism
 Mg application
promoted stepwise 
increases in sunflower
tissue Mg concentration,
and subsequent  Na and
Ca in the plant tissue.
 Nutrient Antagonism with
Nitrogen Potassium
Phosphorus Zinc
Potassium Nitrogen, Calcium, Magnesium
Sodium Potassium, Calcium, Magnesium
Calcium Magnesium, Boron
Magnesium Calcium
Iron Manganese
 before increasing the concentration of one
nutrient in solution to solve a deficiency
problem, need to consider the implications
of this increase on the uptake of other
nutrients
 Such antagonistic effects are not common
among anions, although high levels of Cl- in
a nutrient solution will decrease NO3-
uptake, and vice versa (Mengel and Kirkby,
1982).
 Conversely, it is also true that NO3-
nutrition stimulates the uptake of
cations. This was demonstrated by Kirkby
(1968) who looked at the cation:anion
balance of plants grown with either NO3--
N or NH4+-N as N source
 It is obvious that decisions concerning N
source are important since the ratio of
NO3- to NH4+ affects pH, cation:anion
balance and nutrient interactions that
occurred.
increase concentration of one
ion can increase the uptake of
one or many other cation.
K will also increase Na
Ca = Mg
Ca and B
 Plant roots selectively take up different ions at
different rates.

 the uptake of NO3-, K+ and Cl- are very rapid

compared to the slower uptake of ions such as
Ca2+ and SO42- (Mengel and Kirkby (1982)

 unequal amounts of cations and anions may

be removed from the nutrient solution.
Hiatt (1967): barley roots grown in
solution of K2SO4, KCl, or CaCl2
 K2SO4 : the roots absorbed K+ much
faster than SO4-.
When cation uptake exceeds anion
uptake - the plant will synthesize its
own organic anions (i.e., malate) in
order to maintain its internal
cation:anion balance.
1. pH When cation uptake
 plant roots can, over exceeds anion uptake:
time, effectively change
the pH of the solution  the plant will synthesize
surrounding them by its own organic anions
releasing either H+ or (i.e., malate) in order to
HCO3 ions into the maintain its internal
medium in an attempt to cation:anion balance
maintain their internal
balance of cations
(positively charged ions)
to anions (negatively
charged ions).
 The effect of this excess uptake
of cations on the external
medium would be a decrease in
pH due to H+ excretion by the
plant into the nutrient solution,
again in an attempt by the plant
to maintain an internal balance.
 Conversely, when anion uptake
exceeds cation uptake, such as
with CaCl2, organic anions were
actually degraded and the
external growth medium pH
increased due to excretion of
HCO3- by the plant roots to
compensate for excess anion
uptake.
 Once nutrient uptake has occurred,
there is also a distinct difference
between the ability of the various ions
to move within the plant.
 While N, K, and Mg move freely
throughout the plant, nutrients such
as Ca, B and Fe are much less mobile,
and are translocated in the phloem
sap to much lesser extents
Ca and B occur in minute
concentrations in phloem
sap as compared to K and Mg
reflected in the appearance
of their respective deficiency
symptoms.
 Since K is readily translocated
from older leaves to newly
developing leaves or fruits, when
K supply is inadequate, the
deficiency symptoms will be
observed first in the older leaves.
Conversely, Ca and B do not
move freely in the phloem,
but are greatly dependent
upon the transpiration
stream for their movement in
the plant.
 Consequently, Ca and B
deficiency symptoms are
generally observed in
the apical meristems
of the plant or in low-
transpiring organs
such as developing
fruits, causing such
nutritional disorders as
blossom end rot and tip
die-back of both roots
and shoots.
 Immobile nutrients are dependent
upon the transpiration stream for
their movement, any factors that
affect water uptake or stomatal
opening, i.e., temperature, water
relations, relative humidity, total salt
concentration (electrical
conductivity, EC), will also affect the
uptake and movement of Ca and B in
the plant.
 Therefore, while increasing the
Ca supply to the roots may not
affect the Ca concentration in
fruits enough to solve a blossom
end rot problem, BUT lowering
the EC of nutrient solution or
lowering the relative humidity
in greenhouses might.
 crop being grown,
 growth phase of the crop,
 climatic conditions
 hydroponic growth method
being used.
 Although all plants require the same 16
essential elements), subtle variations in
the amount of individual nutrients are
often recommended for different crops.
one set of macronutrient
recommendations for several crops
grown in rockwool
Recommended nutrient solution levels in ppm (Agrodynamics).

Crop N P K Mg Ca

Tomatoes 200 50 360 45 185

Cucumbers 230 40 315 42 175

Pepper 175 39 235 28 150

Eggplant 175 30 200 20 100

Melon 186 39 235 25 180

Lettuce 200 50 300 65 200

Herbs 210 80 275 67 180

 Species-species recommendations that are
the result of actual research trials designed
to fine-tune the nutrient requirements of a
particular crop should be very helpful in
optimizing the efficiency of plant
production.
 However, it must be noted that even within
a species, different cultivars may have
different requirements.
 The nutritional requirements of a crop
also change as the plant progresses
through different phases of its life
cycle.
 two-step solution for tomatoes which
increased in N and K as fruiting
occurred.
 fruiting crops, especially, have different N requirements
which change with change with growth stage
 recommended a 36% increase in CaNO3 (fruit set)
doubling of CaNO3 use for cucumbers entering their
reproductive stage.
 nutrient solution for tomato seedlings prior to transplant as
well as a five-step series of nutrient solutions (Hochmuth,
1990): which correspond to vegetative growth and four
successive fruiting stages The major changes that occur
are in N and K concentrations, with some increase in Mg
as well.
 Regulation of N : the rate of vegetative
growth.
 High rates of N early in the growth
cycle promote excessive vegetative
growth, often at the expense of fruit
production.
 Plants that become too vegetative, or
“bullish”, from high N exhibit increased leaf
area, dark green coloration, curled leaves
and stems, increased suckering, and big
flower clusters with poor fruit set.

 overly vigorous growth of the shoot often

results in increased blossom end rot
problems, since it leaves less Ca available
to the fruits during their rapid phase of
growth.
 The severity of nutritional disorders
is often intensified by environmental
factors. For examples, blotchy
ripening is often associated with low
light and cool temperatures.
 Conversely, fruit cracking in tomatoes
occurs more readily in bright, hot
weather, especially if the EC of the
growing medium is high. A high EC
nutrient solution can also induce
blossom end rot during periods of low
transpiration (i.e., high relative
humidity) by decreasing both root
pressure and calcium influx into the
fruit (Marschner, 1986).
 Straver and Ingratta (1986) listed
seven factors which needed to be
considered before determining the
ideal EC of a nutrient solution.
 Among these were type of crop,
stage of development and season.
 Currently, many of the recommended
nutrient solution formulas for greenhouse-
grown vegetable crops were developed in
cooler northern climates of Canada of
Holland.
 Therefore, if growing crops in an area with
a very different climate, need to consider
this nutrition management decisions.
 The authors suggested that the reduced
yields at higher EC were due to the low
osmotic potential, and demonstrated that
water absorption by the tomato roots was
strongly reduced by EC values above 3.0
dS.m-1.
 Managing the EC of your nutrient solution
becomes very critical, therefore, with special
attention to keeping the EC low in hot
climates or during the warm season of the
year. This will maintain root pressure and
allow optimal uptake of water and nutrients.
 The last factor to be considered in your
nutrient management decision should be
the growing method
 The main difference occurs between systems
such as rockwool or pear bag culture, where
nutrients are added to the rooting
environment at intervals, and NFT (nutrient
film technique), where a flowing,
recirculating nutrient solution constantly
supplies the roots.
 In the rockwool system, nutrient fluctuation
and depletions occur between waterings as
roots take up the required elements, so that
nutrient recommendations are much in
excess of values typically found in a soil
solution.
 However, in an NFT system, the ions removed by
the roots are continually replenished. plants will
tolerate much lower nutrient levels in an NFT
system and generally have a wider tolerance to
nutrient range (Cooper, 1988).
 For example, Massey and Winsor (1980) grew
tomatoes in shallow troughs containing
recirculating nutrient solution, and found no
significant differences in yield between plants
growing in N concentrations of 0, 20, 40, 80, 160,
and 320 ppm NO3--N.
 over-fertilization, especially with N, is not only
wasteful but may cause environmental concerns.
 Several factors involved in selecting the
proper nutrient solution and in
managing a nutrient program have
been discussed above. These factors
are all important considerations to
ensure that nutrition is not your
limiting factor to achieving maximum
production.
 Jones (1983), “In the past, most growers
were quite satisfied with average
responses from their systems of
growing.
 But, when they begin to reach for
maximum potential, they will discover
that precision in each procedure makes
a difference.
 When growers reach this point in their crop
production systems, hydroponic or
otherwise, the care in making and managing
the nutrient solution may become the
crucial factor in determining their success”.
 Tailoring nutrient solutions to the demands
of your plants is definitely an economically
(and environmentally) sound practice that is
essential for maximizing crop production.