HYDROPONICS/ SOIL-LESS CULTURE
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'Soilless Culture' Book (Sinhala) |
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'Soilless Culture' Book (English) |
Contents of the 'Soilless Culture' Book (English)
Why Hydroponics/ Soil-less Culture?
Hydroponics or soil-less culture is a system of growing
plants which helps reduce some of the above mentioned problems experienced in
conventional crop cultivation.
Hydroponics offers opportunities to provide optimal
conditions for plant growth and therefore, higher yields can be obtained compared
to open field agriculture.
Hydroponics or soil less culture
offers a means of control over soil-borne diseases and pests, which is especially
desirable in the tropics where the life cycles of these organisms continues
uninterrupted and so does the threat of infestation. Thus the costly and time-consuming
tasks of soil sterilization, soil amelioration, etc. can be avoided with hydroponics
system of cultivation. It offers a clean working environment and thus hiring
labour is easy.
Hydroponics/ Soil-less Culture– What is it?
Hydroponics or soil-less culture is a technology for growing plants in nutrient solutions that supply all nutrient elements needed for optimum plant growth with or without the use of an inert medium such as gravel, vermiculite, rockwool, peat moss, saw dust, coir dust, coconut fibre, etc. to provide mechanical support.
Figure 2: Hydroponics lettuce plant
History of HydroponicsHydroponics was practiced many centuries ago in Amazon,
Babylon, Egypt, china and India where ancient men used dissolved manure to grow
cucumber, watermelons and other vegetables in sandy riverbeds. The “hanging
harden of Babylon” and the Aztec’s floating farms were actually prototypes of
hydroponic systems. Later, when plant physiologists started to grow plants with
specific nutrients for experimental purposes, they gave the name “nutriculture.”
Interest in practical application of “nutriculture” developed in 1925 when the
green house industry expressed interest in its use. Green house soils had to
be replaced frequently to overcome problems of soil structure, fertility and
pests. As a result, researchers became interested in the potential use of nutriculture
to replace conventional soil culture.
In
1929, Dr William F. Gericke of the University of California succeeded in growing
tomato vines of 7.5 m height in nutrient solutions. He named this new production
system “hydroponics” a word derived from Greek to reflect the importance of
‘Hydros’ (water) and ‘Ponos’ (working). Thus, hydroponics broke the laboratory
bounds and entered the world of practical horticulture. The term hydroponics
originally meant nutrient solution culture. However, crop growing in inert solid
media using nutrient solution is also included in hydroponics in broad sense.
During
1960s and 70s, commercial hydroponics farms were developed in Abu Dhabi, Arizona,
Belgium, California, Denmark, German, Holland, Iran, Italy, Japan, Russian Federation
and other countries. During 1980s, many automated and computerized hydroponics
farms were established around the world. Home hydroponics kits became popular
during 1990s.
In Sri Lanka, the hydroponics system of cultivation is in its infancy. Many
use inert solid medium such as coconut fibre or coir-dust with fertigation and
some use balanced nutrient solution alone employing both circulating and non-circulating
methods in small and medium scales.
Figure 4: Hydroponics strawbery plants in a net house
Soils
naturally maintain the temperature and aeration needed for root growth. When
the soil is poor, plant growth and yield decline also due to unsuitable aeration
and temperature. Plant cultivation is impossible under ill drained condition
due to these conditions. Soil adjusts itself to provide suitable conditions
for plant growth. It is called the buffer action of the soils. Plants also absorb
nutrients released through natural mineralization.
In a solution or inert medium, maintenance of
acidity or alkalinity (pH) and electrical conductivity (EC) in suitable ranges
for plant root system is called buffer action. This requirement must be artificially
maintained in hydroponics. In any hydroponics system the following basic requirements
must be maintained at optimum levels.
•
Buffer action of water or the inert medium used.
• The nutrient
solution or the fertilizer mixture used must contain all micro and macro elements
necessary for plant growth and development.
• Buffer action
of the nutrient solution must be in the suitable range so that plant root system
or the inert medium is not affected.
• The temperature and
aeration of the inert medium or the nutrient solution is suitable for plant
root system.
Classification of Hydroponics/ Soil-less Culture
The term hydroponics originally meant nutrient solution
culture with no supporting medium. However, plant growing in solid media for
anchorage using nutrient solution is also included in hydroponics. This technique
is called aggregate system. Hydroponics systems are further categorized as open
(i.e., once the nutrient solution is delivered to the plant roots, it is not
reused) or closed (i.e., surplus solution is recovered, replenished and recycled).
Current hydroponics systems of cultivation can be classified according to the
techniques employed. A hydroponic technique refers to the method of applying
nutrient solution to the plant roots.
Large numbers of hydroponic techniques are available.
However, consider following factors in selecting a technique.
• Space and other resources
available
• Expected productivity
• Availability of suitable growing medium
• Expected quality of the produce – colour, appearance,
free from pesticides, etc.
1.
Solution culture or Liquid hydroponics -Circulating methods (closed system)
Nutrient film technique (NFT)
Deep flow technique (DFT)
Non-circulating method (open systems) Root dipping technique
Floating technique Capillary action technique
2.
Solid media culture (Aggregate systems)
These can be open systems or closed systems.
Hanging bag technique
Grow bag technique
Trench or trough technique
Pot technique
3. Aeroponics -Root mist technique
Fog feed technique
Liquid
or Solution Culture
CIRCULATING METHODS
The nutrient solution is pumped through the plant root system and excess solution is collected, replenished and reused in these methods.
Nutrient
Film Technique (NFT)
NFT is a true hydroponics system where the plant roots
are directly exposed to nutrient solution. A thin film (0.5 mm) of nutrient
solution flows through channels. The main features of a NFT system are shown
in figure 5.
The channel is made of flexible sheet. The seedlings
with little growing medium are placed at the centre of the sheet and both edges
are drawn to the base of the seedlings and clipped together (Figure 6) to prevent
evaporation and to exclude light. The cross section of the channel is shown
in figure 7. The growing medium absorbs nutrient solution for young plants and
when the plants grow the roots form a mat in the channels.
Figure 5: Main features of a NFT system
Figure 6: Basic structures of a NFT channel Figure7:
Cross Section of a NFT chann
The maximum length of the channel is 5-10 m and is placed
at a slope drop of 1 in 50 to 1 in 75. The nutrient solution is pumped to the
higher end of each channel and flows by gravity to the lower end wetting the
root mat.
At lower end of the channels nutrient solution gets
collected and flows to the nutrient solution tank. The solution is monitored
for salt concentration before recycling. Some growers replace the nutrient solution
every week with fresh solution.
Adjust the flow rate of the nutrient solution to 2-3 litres per minute depending
on the length of the channel. Provide enough support for tall growing plants
in this technique.
In practice, it is very difficult to maintain a very thin film of nutrient solution
and therefore, this technique has undergone several modifications.
Deep Flow Technique (DFT) – Pipe
System
As the name implies, 2-3 cm deep nutrient
solution flows through 10 cm diameter PVC pipes to which plastic net pots with
plants are fitted. The plastic pots contain planting materials and their bottoms
touch the nutrient solution that flows in the pipes. The PVC pipes may be arranged
in one plane or in zig zag shape depending on the types of crops grown. The
figure 8 and 10 below shows the main features of a DFT – pipe system.
Figure 8: An illustration of a single plane pipe system DFT
The zig zag system utilizes the space efficiently but suitable for low growing crops. The single plane system is suitable for both tall and short crops.
Figure 9: A Single plane pipe system DFT Figure
11: A zig zag pipe system DFT
Figure 10: An illustration of a zig zag pipe system
DFT Net pot
plastic
potzz
Net pot with
established plant Plastic
pot with established plant
Plants are established in plastic net pots and fixed
to the holes made in the PVC pipes. Old coir dust or carbonised rice husk or
mixture of both may be used as planting material to fill the net pots. Place
a small piece of net as a lining in the net pots to prevent the planting material
falling into the nutrient solution. Small plastic cups with holes on the sides
and bottom may be used instead of net pots.
Figure 13: Cross section of a PVC pipe system DFT
When the recycled solution falls into the solution in the stock tank, the nutrient solution gets aerated. The PVC pipes must have a slope of drop of 1 in 30-40 to facilitate the flow of nutrient solution. Painting the PVC pipes white will help reduce the heating up of nutrient solution. This system can be established in the open space or in protected structures as part of CEA.
The nutrient solution is not circulated but used only once. When its nutrient concentration decreases or pH or EC changes, it is replaced.
Root
Dipping Technique
In this technique, plants are grown in small pots filled
with little growing medium. The pots are placed in such a way that lower 2 -
3 cm of the pots is submerged in the nutrient solution (figure 14). Some roots
are dipped in the solution while others hang in the air above the solution for
nutrient and air absorption, respectively.
This technique is easy and can be developed using easily
available materials. This ‘low tech’ growing method is inexpensive to construct
and needs little maintenance. Importantly, this technique does not require expensive
items such as electricity, water pump, channels, etc. For root crops (beet,
raddish, etc.) however, an inert medium has to be used.
Figure 14: Diagrammatic view of a non-circulating hydroponics
non-root tuber plant
1. Root dipping technique for non-root tuber crops
First, select a container for nutrient solution. The
container can be almost any kind and shape except metal containers. Styrofoam
or wooden boxes, plastic buckets or even cement troughs can be used. Styrofoam
boxes are good as they can maintain the temperature of the nutrient solution.
Place a black plastic sheet of at least 0.15 mm thickness as lining inside the
boxes to avoid leakage and to reduce the light (figure 15). The depth of the
box must be about 25 – 30 cm to provide enough solution as well as enough space
above the solution for oxygen absorbing roots.
Figure 15: Container with black polythene lining
A board is required to place on the container to prevent light penetration. The planting pots are also fixed to this board (figure 16). The number of holes in the board to fix the pots depends on the crops to be grown. An additional hole is necessary for air circulation and refilling.
Figure 16: Boards with holes to cover the box and to
which pots are fixed
Figure 17: planting pots
The above steps complete the formation of non-circulating
hydroponics system. These boxes can be placed in net houses or in open space
or under rain shelters or in-door. Tall growing plants will require some support
to prevent from falling.
Figure 18: Potted plants fixed to the board to cover
the container
Maintain adequate air space above the nutrient solution in the container. Success of the non-circulating hydroponics system depends on the rapid growth and quantity of roots that are exposed to the air. These roots absorb oxygen for the plants. Ideally, top two
Figure 19: Non-circulating hydroponic plants growing
in a Styrofoam box
thirds
of the young root system must be in the air and the rest must be floating/dipping
in the nutrient solution.
During crop growth, when the solution level in
the container goes down, the ion concentration may increase. Such increase is
detrimental to plant growth. If this condition is observed, siphon out the remaining
solution and refill with fresh solution.
Figure 20: Diagrammatic view of the root dipping technique
for root tuber crops
At the early stage, nutrient solution will reach the planting medium through
the perforated PVC pipe filled with the growing medium by capillary action.
Later, plant roots will grow into the nutrient solution through wire mesh. At
this stage, the perforated tube will be removed. The resulting hole will facilitate
aeration and refilling.
Floating Technique
This is similar to box method but shallow containers
(10 cm deep) can be used. Plants established in small pots are fixed to a Styrofoam
sheet or any other light plate and allowed to float on the nutrient solution
filled in the container (Figure 21) and solution is artificially aerated.
Planting pots of different sizes and shapes with holes
at the bottom are used. Fill these pots with an inert medium and plant seedlings/seeds
in that inert medium. These pots are placed in shallow containers filled with
the nutrient solution. Nutrient solution reaches inert medium by capillary action
(Figure 22).
Figure 21: Diagrammatic view of floating technique Figure
20: Diagrammatic view of the root dipping technique for root tuber crops
Capillary
Action Technique
Aeration is very important in this technique. Therefore,
old coir dust mixed with sand or gravel can be used. This technique is suitable
for ornamental, flower and indoor plants.
Solid Media Culture
or Aggregate System
The following techniques involving inert solid media
can be practiced using locally available materials. The media material selected
must be flexible, friable, with water and air holding capacity and can be drained
easily. In addition, it must be free of toxic substances, pests, disease causing
microorganisms, nematodes, etc. The medium used must be thoroughly sterilized
before use.
• Inorganic natural media (gravel culture)
• Organic natural media (smoked rice husk, saw dust, coconut fibre, coir dust
peat moss)
• Inorganic artificial media (rockwool, perlite, vermiculite)
• Organic artificial media (polyurethane, polyphenol, polyether, polyvinyl)
Tanins and acids present in the newly extracted
coir-dust affect plants. Therefore, use at least 06 months old coir-dust. Dry,
clean compressed coir-dust blocks are available for sale in the market.
Different techniques described below, according
to the method of holding the planting medium, can be practiced.
Hanging
Bag Technique (Open system)
About 1 m long cylinder shaped, white (interior black)
UV treated, thick polythene bags, filled with sterilized coconut fibre are used.
These bags are sealed at the bottom end and tied to small PVC pipe at the top.
These bags are suspended vertically from an overhead
support above a nutrient solution-collecting channel. Therefore, this technique
is also knows as ‘verti-grow’ technique. Seedlings or other planting materials
established in net pots are squeezed into holes on the sides of the hanging
bags. The nutrient solution is pumped to top of each hanging bag through a micro
sprinkler attached inside the hanging bags at the top. This micro sprinkler
evenly distributes the nutrient solution inside the hanging bag. Nutrient solution
drips down wetting the coconut fibre and plant roots. Excess solution gets collected
in the channel below through holes made at the bottom of the hanging bags and
flows back to the nutrient solution stock tank (Figure 23).
This system can be established in the open space
or in protected structures. In protected structures, the hanging bags in the
rows and amongst the rows must be spaced in such a way that adequate sunlight
falls on the bags in the inner rows.
Figure 23: Diagrammatic view of hanging bag technique Figure
24: Strawbery plants growing in hanging
The bags are not heavy as they are filled
with coconut fibre and can be used for about 02 years. The number of plants
per bag varies depending on the plants. About 20 lettuce plants can be established
per bag. This system is suitable for leafy vegetables, strawberry, and small
flower plants. Black colour tubes will have to be used for nutrient solution
delivery to prevent mould growth inside.
Figure 25: Diagrammatic view of plants in grow bags
the
coir-dust. 2-3 plants can be established per bag. Make 02 small slits low on
each side of the bags for drainage or leaching.
Fertigation with black capillary tube leading
from main supply line to each plant is practiced. The nutrient solution and
water may also be added manually to these bags. Depending on the stage of crop
growth and the prevailing weather conditions, vary the
Figure 26: Tomato plants growing in grow bags
amount
of water applied. Make sure that the growing media is not completely saturated
with water or nutrient solution, as it prevents the oxygen supply to plant roots.
Cover the entire floor with white UV resistant
polythene before placing the bags. This white polythene reflects the sunlight
to the plants. It also reduces the relative humidity in between plants and incidence
of fungal diseases. When tall growing plants are established supporting structures
will be necessary.
Trench
or Trough Technique
In this open system, plants are grown in narrow trenches
in the ground (Figure 27) or above ground troughs (figure 28) constructed with
bricks or concrete blocks.
Both trenches and troughs are lined with waterproof
material (thick UV resistant polythene sheets in two layers) to separate the
growing media from rest of the ground. The width of the trench or trough can
be decided depending on the ease of operation. Wider trenches or troughs will
permit two rows of plants. The depth varies depending on the plants to grow
and a minimum of 30 cm may be necessary.
Figure 27: Cross section of hydroponic trenches Figure 28: Cross section of above ground troughs
Old
coir dust, sand or gravel, peat, vermiculite, perlite, old sawdust or mixture
of these materials can be used as the media for this culture. The nutrient solution
and water are supplied through a drip irrigation system or manual application
is also possible subject to labour availability. A well-perforated pipe of 2.5
cm diameter may be placed at the bottom of the trough or trench to drain out
excess nutrient solution.
Tall growing vine plants (cucumber, tomato, etc.)
need additional support to withstand the weight of the fruits.
Pot Technique
Pot technique is similar to trench or trough culture
but growing media is filled in clay or plastic pots (Figure 29). Volume of the
container and growing media depend on the crop growth requirements. The volume
ranges generally from 01 to 10 litres.
Growing media, nutrient solution supply, providing
support to plants, etc. is similar to that of trough or trench culture.
Aeroponic
Technique
Aeroponic is a method of growing plants where they are
anchored in holes in Styrofoam panels and their roots are suspended in air beneath
the panel. The panels compose a sealed box to prevent light penetration to encourage
root growth and prevent algae growth. The nutrient solution is sprayed in fine
mist form to the roots. Misting is done for a few seconds every 2 – 3 minutes.
This is sufficient to keep roots moist and nutrient solution aerated. The plants
obtain nutrients and water from the solution film that adheres to the roots.
Figure 29: Hydroponics plants in pot technique
The
aeroponic culture is usually practiced in protected structures and is suitable
for low leafy vegetables like lettuce, spinach, etc.
The principal advantage of this technique is
the maximum utilization of space. In this technique twice as many plants may
be accommodated per unit floor area as in other systems. Another potential application
of this technique is in the production of plants free of soil particles from
cuttings for exports.
Figure 30: Aeroponic A-frame unit, developed by Jensen
and Collins in 1985 at the University of Arizona
As in open field agriculture, production of vigorous
seedlings or planting material of high yielding varieties is an essential step
of hydroponics/soil-less culture, to obtain economic yields.
Nursery Medium
The growing medium must provide satisfactory conditions
for seed germination and to raise pest and disease free seedlings. A material
that is friable, moderately fertile, well drained yet have sufficient water
holding capacity and good aeration and free of pests and disease causing organisms
must be selected as medium for seed germination or rooting the planting materials.
The following materials can be used as medium
to raise seedlings or to root planting materials.
- Old coir-dust
- Carbonised rice husk
- Fine sand or fine sand and old coir dust
mixture
- Rockwool, Peat, perlite or vermiculite,
etc.
Sterilize the medium before use. For coir-dust,
add hydrated lime to bring its pH to neutral. For a 05 kg coir-dust block, about
100 – 250 g hydrated lime is needed.
Nursery Containers/ Trays
Use a container that provides the suitable condition
for seed germination and also according to crop and cultivation method.
Individual containers / Growing
blocks:
paper pots, plastic pots, clay pots,
Styrofoam pots, coconut fibre pots, rockwool blocks,
sponge blocks
Figure 31: Some individual containers Figure
32: Trays
Trays: Styrofoam trays, seedling/cell plug trays
Trays made up of different materials are available for sale in market. Depending on the requirements, trays may be selected.
Seed
Germination
Thorough cleaning of the pots followed by washing with
10% Calcium or Sodium hypochloride will ensure disease free condition. Place
one seed per block filled with growing medium at the correct depth in the pots
or trays.
Such necessary conditions for seed germination
as moisture, temperature, humidity must be provided. Germination trays can be
covered with wet papers or cloth to provide adequate temperature for germination
until the seeds sprout. Remove these papers at the time of seedling emergence.
Maintain the moisture level of the medium at
correct level for uniform germination and application of water in the mornings
is preferred.
Vegetative parts separated from mother plants can also be rooted and used as planting materials. Individual containers or trays filled with growing medium are used for rooting these vegetative parts. Select vegetative parts that are free from pests, disease causing organisms and nematodes for propagation. For example, following materials can be used for propagation.
Figure 33: Selected Kang Kong stem cutting
| Gotukola | Plantlets or runners separated from mother plants. |
| Strawberry | Plantlets or runners separated from mother plants |
| Gerbera | Plantlets separated from mother plants |
| Mukunuwenna | 10 – 12 cm long semi- hardwood or hardwood stem cuttings. |
| Kang Kong | 20 cm long semi-hardwood cuttings with 3-4 nodes. |
| Mint | 10 – 12 cm long semi-hardwood stem cuttings |
| Sarana | Semi-hardwood stem cuttings. |
Figure 34: Rooted Kang Kong stem cutting ready for planting
Nutrient supply is not necessary until the emergence
of first two true leaves. Until such time apply only clean water. However, when
they unfold, nutrient supply must begin gradually as the growing medium contains
very little plant nutrients. The fertilizer mixture meant hydroponics plants
could also be used for nursery plants. Diluted nutrient solution can be applied
every day or nutrient solution prepared by dissolving 10 g of Albert’s mixture
in 10 litre of water can applied every other day.
At the early stage, place the trays or pots in
shallow containers that is filled with nutrient solution in such a way that
the tray’s or pots’ lower portion is submerged in the solution. The nutrient
solution will reach the media through the holes at the bottom of the pots or
nursery trays by capillary action. Vegetative parts for propagation planted
in individual containers or trays are also placed in shallow nutrient solution
containers as seedling trays.
Figure 35: Nursery pots placed in shallow nutrient solution containers
The
nutrient solution can also be applied directly to nursery pots after seed germination
or sprouting of planting materials. When applying nutrient solution directly
to nursery pots,
•
place the pots or trays on a flat plane and pour solution so that it does not
come into direct contact with the small plant;
• at the early stage apply 5-10 ml solution
once a day; and
• when plants grow, 10-25 ml a day once
or twice till establishment.
Once the seedlings or planting materials reach
the correct size for planting, they can be planted with the medium. Vegetative
parts can sometimes be directly established in the hydroponics system.
The nursery period varies with the crops.
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Select vigorous seedlings with the characteristics for the variety concerned for establishment in hydroponics. Also tissue-cultured plants can be established in hydroponics.
Sponge pieces can be used as nursery medium instead
of the above mentioned media materials. 2.5 cm cube sponge blocks can be used
for this purpose. Place the seeds at the centre in a cut made on the topside
of the sponge block.
Sponge nursery is maintained as other nurseries. Nutrient
supply must begin when the first true leaf begin to unfold. Depending on the
cultivation method, the seedlings can be planted in hydroponics system with
the sponge block intact. The sponge block may be removed with minimum damage
to roots when plants begin to grow .
Figure 36: Sponge block for seed germination Figure 37: Seedling in a sponge block ready for transplanting
Nutrient Solution for Hydroponics
Figure 38: Plant nutrients in nutrient solution
as management of plant nutrition through management
of nutrient solution is the key to success in hydroponic gardening.
The hydroponic methods enable growers to control
the availability of essential elements by adjusting or changing the nutrient
solution to suit the plant growth stage and to provide them in balanced amounts.
As the nutrients are present in ionic forms in the nutrient solution and also,
not needing to search or compete for available nutrients as they do in soil,
hydroponic plants reach maturity much sooner. Optimization of plant nutrition
is easily achieved in hydroponics than in soil.
Nutrient Solution Management
While optimum nutrition is easy to achieve in hydroponics,
incorrect management of the nutrient solution can damage the plants and lead
to complete failure. The success or failure of a hydroponic garden therefore,
depends primarily on the strict nutrient management programme. Carefully manipulating
the nutrient solution pH level, temperature and electrical conductivity and
replacing the solution whenever necessary, will lead to a successful hydroponic
garden.
pH Level
In simple terms, pH is a measure of acidity or alkalinity
on a scale of 1 to 14. In a nutrient solution, pH determines the availability
of essential plant elements. A solution is considered to be neutral at pH 7.0,
alkaline if above and acidic if below.
For pH values above 7.5, iron, manganese, copper, zinc and boron becomes less
available to plants. Should the pH of a nutrient solution fall below 6.0, then
the solubility of phosphoric acid, calcium and manganese drops sharply. The
optimum pH range for hydroponic nutrient solution is between 5.8 and 6.5.
Figure 39: Measuring nutrient solution pH using a portable
digital pH meter
The further the pH of a nutrient solution from
recommended pH range, the greater the odds against the success.
The figure 40 indicates the nutrient element
availability at different pH levels of the solution. Nutrient deficiencies will
become apparent or toxicity symptoms will develop if the pH is higher or lower
than the recommended range for individual crops. For example, if pH is consistently
7.5, one can expect intra-veinal chlorosis to occur, an indication of iron deficiency.
Figure 40: Chart showing the availability of nutrient
elements at different pH levels.
The
chart shows a pH range of 4.0 to 10.0. The width of the coloured section for
each nutrient represents the availability of that nutrient. The widest place
denotes the maximum availability. The narrowest place denotes the least availability.
The red line at pH 6.25 indicates the maximum number of elements at their highest
availability.
When plants absorb nutrients and water from solution,
pH of the solution changes. Therefore, it must be monitored daily, and adjusted
to be between the recommended ranges. Chemical buffers can adjust the pH of
a nutrient solution, when it strays outside the ideal. It can be lowered by
adding dilute concentrations of phosphoric or nitric acids and raised by adding
a dilute concentration of potassium hydroxide. Although it is important to stay
within recommended range, it is far more important to prevent large fluctuations.
Electrical
Conductivity (EC)
The electrical conductivity indicates the strength of
nutrient solution, as measured by an EC meter. The unit for measuring EC is
dS/m. A limitation of EC is that it indicates only the total concentration of
the solution and not the individual nutrient components.
The ideal EC range for hydroponics is between
1.5 and 2.5 Ds/m. Higher EC will prevent nutrient absorption due to osmotic
pressure and lower EC severely affect plant health and yield.
Figure 39: Measuring nutrient solution pH using a portable
digital pH meter
When plants take up nutrients and water from the solution, the total salt concentration, i.e., the EC of the solution changes. If the EC is higher than the recommended range, fresh water must be added to reduce it. If it is lower, add nutrients to raise it.
Preparation
of Nutrient Solution
Though hydroponic growers can formulate their own fertilizer
mixtures to prepare nutrient solutions using completely water-soluble nutrients
salts, a number of formulations are available in the market to choose.
It is important to avoid any formulations that
contain impurities like sand, clay or silt. Such impurities do not supply any
nutrients but they are harmful as they can block the delivery tubes.
Also avoid any formulation that has insoluble
or less soluble salts. In hydroponics, the nutrients must be available in solution
in ionic form for plant absorption. If they are found as salts, plants will
suffer from nutrient deficiency symptoms.
Although urea is completely soluble in water,
it cannot be used in hydroponics, as it does not break into ionic form in the
solution as it does in soils.
Some fertilizer salts react with each other to
produce insoluble precipitations. For example, ammonium sulphate and potassium
chloride form less soluble potassium sulphate in the tank. Phosphate fertilizers
act problematic in the presence of high calcium and magnesium concentrations,
causing precipitation of low soluble phosphates. Therefore, select fertilizers
that are compatible with each other. The table 1 indicates compatibility of
some salts.
Table 1: Compatibility chart for some soluble fertilizers
|
Solublefertilizers |
AN
|
AS
|
CAN
|
MAP
|
SOP
|
MOP
|
|
Ammonium nitrate (AN) |
-
|
c
|
c
|
c
|
c
|
c
|
|
Ammonium sulphate (AS) |
c
|
-
|
l
|
-
|
c
|
c
|
|
Calcium nitrate (CAN) |
c
|
l
|
-
|
x
|
c
|
c
|
|
Mono ammonium phosphate(MAP) |
c
|
c
|
x
|
-
|
c
|
c
|
|
Potassium sulphate (SOP) |
c
|
c
|
l
|
c
|
-
|
c
|
|
Potassium chloride (MOP) |
c
|
c
|
x
|
c
|
c
|
-
|
|
Gypsum (G) |
x
|
x
|
x
|
x
|
c
|
c
|
|
Kieserite (KS) |
c
|
c
|
c
|
x
|
c
|
c
|
|
Potassium nitrate (PN) |
c
|
l
|
c
|
c
|
-
|
c
|
C: compatible, can be mixed in the solution L: Limited compatibility, mix at the time of use or some precautions must be taken X: Incompatible, do not mix
Fertilizer Mixtures
for Hydroponics
The tables 2 and 3 give nutrient salt contents of two
hydroponics formulations.
These fertilizer mixtures are not suitable as
foliar spray as the EDTA iron (iron chelate) does not disintegrate easily on
plant surface and therefore, can be harmful to consumers.
Table 2: Chemicals needed to prepare 1000 litres of nutrient solution proposed by Dr Alan Cooper.
|
Weight in grams
|
|
263.00
|
|
583.00
|
|
1003.00
|
|
513.00
|
|
79.00
|
|
6.10
|
|
1.70
|
|
0.39
|
|
0.37
|
|
0.44
|
Table 3: Chemicals needed to prepare 1000 litres of nutrient solution (Albert’s mixture, locally available in the market).
|
Weight in grams
|
|
38.00
|
|
952.00
|
|
308.00
|
|
8.00
|
|
0.15
|
|
0.20
|
|
1.15
|
|
0.10
|
|
269.00
|
|
423.00
|
|
0.03
|
Figure 42: Fertilizer mixing tank
Fertigation
Fertigation combines the two main factors of supplying
water and plant nutrients that are essential for plant growth. The right combination
of the two is the key to obtain high yields and quality produce.
Advantages of Fertigation
• Accurate and uniform application of fertilizers
• Ability to meet plant nutrient demand under given
climatic conditions and during different crop growth stages
• Improving fertilizer use efficiency and reducing leaching
below root zone thus minimizing pollution
• Saving on labour
• Increasing both yield and quality of produce
Factors to be Considered in Fertigation
1. Growing media
2. Fertilizers used
3. Irrigation water quality
As the first two factors were discussed earlier,
only irrigation water quality is discussed here.
Irrigation Water Quality
Use good quality water with its pH and EC suitable for
plant growth. Based on pH, EC and soluble salt content, water quality can be
divided into 03 classes
(Table 4).
Non-hazardous and medium class water can be used
for fertigation. However, when latter is used for fertigation, thoroughly leach
the growing medium at least once a year.
Methods of Fertigation
Mix the fertilizers required for a particular crop with
daily water requirement of that crop and apply manually or through fertigation
system.
The
amounts of fertilizers mixed with irrigation water will vary depending on the
crops, crop growth stage and the hydroponics technique used. The example below
explains this situation.
However, at all stages of crop growth, the pH
of the nutrient solution must be maintained between 5.8 - 6.5 and EC between
1.5 - 2.5 Ds/m.
For circulating techniques (DFT and NFT), supply
the nutrient solution for a predetermined time period.
For aggregate systems (solid media culture),
fertigation can be done manually or through drip irrigation system. Supply the
fertilizers with irrigation water for a predetermined time period so that the
water content of the growing media does not increase beyond field capacity.
When fertigation is not done, the crop must be irrigated with water to maintain
the medium at field capacity.
Table 4: Irrigation water quality classes
|
Quality Factors |
Unit
|
Water Quality classes
|
||
|
|
Non-hazardous
|
Slight to Moderate
|
Severe
|
|
|
pH |
--- Normal Range 6.5 - 8.4 ---
|
|||
|
Salinity Ecw |
Ds/m
|
0.00 – 0.8
|
0.8 – 3.0
|
>3
|
|
Sodium |
me/lit
|
<3
|
<3
|
-
|
|
Chloride |
me/lit
|
<3
|
<3
|
-
|
|
Boron |
me/lit
|
<0.7
|
0.7-3
|
>3
|
|
Bicarbonates |
me/lit
|
<1.5
|
1.5-8.5
|
>8.5
|
In hydroponics, the growing medium does not provide
enough anchorage as soils. This is more so in liquid cultures as no planting
medium is used. Therefore, growers must provide artificial supporting structures
and train plants along those structures. Support is especially important, when
tall growing indeterminate type crop varieties (tomatoes, cucumber, etc.) or
crops bearing relatively heavy fruits (bell pepper, egg plant, etc.) are used
in hydroponics.
A polythene string can be tied at the base of
each plant using a plastic plant clip or by a loose non-slip knot as shown in
figure 43 and the string is tied vertically to the overhead horizontal support
to hold the plants. When plants grow, wind the main stems loosely around the
string for support. In the case of tall growing indeterminate tomato varieties,
placing additional plant clips every 3rd to 4th nodes will be necessary to prevent
the plants from slipping down.
For salad cucumbers, the vertical string is attached
to each plant with plastic plant clips or by a loose non-slip knot at the base.
As the plants grow, wind the main stem loosely around the string for support.
Additional plant clips are attached to prevent plants from slipping.
Tall growing indeterminate type tomatoes are
trained to a single stem. All lateral branches are removed when they are about
5 cm long (Figure 44). Prune the lateral branches every 3 – 4 days, and it is
best done early in the day.
Indeterminate type tomato plants that produce
long term crops are lowered to a working height as they grow, keeping production
limited to fruit grown on the 2 – 2.5 m of the main stem. When plants grow taller,
remove about 04 leaves at the bottom and untie
Figure 43: Training plants on vertical support.
the string from the overhead horizontal support and lower the plants about 60 cm and tie the string shifting to a side (figure 45). This must be done every 2 weeks, and the strings must be long enough to permit lowering during the entire cropping period.
Figure 44: Removal of side branches in tomato plants
Tomatoes
produce large number of fruits at each cluster. To get large, quality fruits,
fruit thing will be necessary. Depending on the size required, 3 to 5 fruits
may be left in a cluster.
For salad cucumbers, umbrella system of pruning
can be adopted. It involves pruning all lateral branches until the plant reaches
the overhead horizontal support (figure 46). There, the terminal bud is removed
and two side branches are allowed to grow downwards. Vigorous plants will continue
to produce fruits
Figure 45: Tomato plant at left will be lowered the
position at right by retying the support string to the overhead horizontal support
several cm to the right
on
the downward growing lateral branches, although the rate of fruit production
tends to slow down.
Salad cucumber may produce more than one fruit
per node; these can be thinned out to one fruit per node or allowed to develop
if they are not curved or otherwise distorted in shape. Heavy fruiting at lower
part of the vine will reduce production higher up.
Figure 46: The umbrella training system for cucumber
Bell pepper plants are trained to two stems. Vertical strings tied to overhead horizontal support, support them. Guide these side stems to the vertical strings. Flowers occur in axils of each branch. Side shoots arising from the stems must be pruned after 2 – 3 leaves so that fruiting takes place only on the two main branches. Periodic fruit thinning may be required to obtain large, good quality fruits.
Management Requirements of Hydroponics/ Soil-less Culture
Meet the following requirements to develop and maintain
a successful hydroponics/soil-less cultivation of crops. If any of these conditions
are not fulfilled, one cannot obtain economical yields.
• Maintain the nutrient solution pH in the range
of 5.8 to 6.5, and electrical conductivity (EC) in the range of 1.5 to 2.5 Ds/m,
as these ranges are suitable for plant growth. Any pH or EC outside these ranges
will reduce availability and uptake of nutrients and will also damage plant
roots.
Plants are the best indicators of the nutrient
availability. Look for nutritional disorder symptoms in plants and adjust nutrient
solution accordingly (Figure 47).
Figure 47: Iron deficiency symptom in strawberry
Avoid any sudden changes in nutrient solution concentration
as it can result in unsuitable pH and EC
• Maintain adequate solution temperature. As
the temperature goes up, plant respiration increases causing a higher demand
for oxygen. At the same time, the solubility of oxygen decreases. This requirement
is more critical in green houses and net houses where the temperature is bound
to increase during mid afternoons. Steps must be taken to counter such increase.
•
Always ensure that there is plenty of dissolved oxygen in the nutrient solution
as the plant roots absorb oxygen. Lack of oxygen will reduces up take of nutrients
and thereby the yield and also causes root rot. In closed systems, if the recollected
solution is allowed to fall into the solution tank from a height, natural aeration
will take place.
In root dipping techniques, maintain adequate
air space above the nutrient solution in the container as success depends on
the rapid growth and quantity of roots that are exposed to the air. These roots
absorb oxygen for the plants. Ideally, top two thirds of the young root system
must be in the air and the rest must be floating in the nutrient solution.
Figure 48: Luxuriant growth of water and air absorbing
roots takes place when there is adequate air space above solution
•
In root dipping techniques, during crop growth, when the solution level in the
container goes down, the ion concentration may increase. Such increase is detrimental
to plant growth. If this condition is observed, siphon out the remaining solution
and refill with fresh solution.
•
Ensure adequate light for the hydroponics/soil-less culture plants. Light and
all other requirements are the same as though grown in open fields.
• Always use pest and disease free seedlings and planting materials for establishment
of hydroponics crops. Remove and destroy any infected plants as soon as they
are found.
• If nematode problem is observed in solid media culture, discard the plants
and sterilize the growing medium. If in doubt, discard and replace the medium.
Also ensure that he water supply is also free from nematodes.
• Algae can build up in the system and block the small tubes used for the delivery
of nutrient solution. Use black colour tubes to avoid such problems. Between
crops, thoroughly clean the system using a mild solution of chlorine. After
cleaning, thoroughly flush the system with fresh water before replanting.
• Adequate spacing is necessary for plant growth and when vine crops are grown,
supports must be provided.
• In open aggregate techniques, there is a possibility for nutrients to leach
when water is applied. Therefore nutrient solution may be applied continuously
instead of water to supply both water and nutrients.
Hydroponics culture is probably the most intensive method of crop production in today’s agricultural industry. In combination with green houses and protective covers (controlled environment agriculture), it is high technology and capital intensive. With the possibility of adjusting air and root temperature, light, water, plant nutrition, and adverse climate, this combination can be made highly productive, conservative of water and land and protective of the environment.
Figure 49: Protected
structure
Advantages
High-density maximum crop yield, crop production where
no suitable land exists, crop cultivation regardless of seasonality, more efficient
use of water and fertilizers and minimal use of land area are the principal
advantages of soil-less culture in combination with controlled environment agriculture.
Another major benefit is the possibility of obtaining pesticide free products,
which fetch higher prices at the increasingly ready markets, at present.
Precautions
High temperature
One serious concern in Sri Lanka and other tropical
countries is the rise of solution temperature during mid afternoons in green/net
houses and under protective covers. Adoption of closed system of hydroponics
where the solution is recycled helps reduce such rise in temperature to some
extend. Further, misting of water to crops when temperature rises, use of exhaust
fans, use of white colour containers to hold solutions, painting gullies/pipes
with white colour, etc. will help reduce the build up of heat from sunlight.
Sunlight
In protected structures, it was observed that growth
and yield of plants of inner rows of hanging bag and grow bag techniques were
poor due to low sunlight availability. Therefore, ensure that enough sunlight
reaches the inner rows of these techniques.
Pollination
As protected structures effectively prevent insects
reaching crops, pollination by insects does not take place in the protected
structures. Also lack of natural airflow also reduces the chances of natural
pollination. High temperatures normally experienced inside protected structures
also interfere with pollination as it reduces pollen viability. Therefore, artificial
pollination must be done by the use of mechanical vibrators. Blowers can be
used to improve the airflow inside the structures.
hormones may also be used to increase the chances
of pollination inside protected structures. For example, 0.15% 4-CPA (Para chlorophenoxy
acetic acid - a kind of auxin) is widely used to induce fruiting of tomato in
Japan. Hormone application is effective for tomato 3 days before and 3 days
after blooming. Application more than once, higher concentration or too early
application can result in malformed fruits.
Some Problems and Solutions in Hydroponics
As experienced in normal crop husbandry, pests diseases and too affect hydroponics plants and they also show physiological as well as nutritional disorders under unfavourable conditions.
Physiological Disorders
Sudden changes in environmental factors, incorrect nutrition
supply or irrigation can bring about physiological disorder symptoms in plants.
Some crop varieties are more prone to these conditions than others.
Blossom end rot of tomato
At the bottom end of tomato fruits, brown, sunken leathery
spots appear (Figure 50). Calcium deficiency, dry growing medium and sudden
supply of water, salt accumulation in root zone are some causal factors. Avoiding
these conditions will prevent blossom end rot.
Figure 50: Blossom end rot of tomato
Figure 52: Cracks extending from stalk
Figure 51: Concentric fruit cracking of tomato
Shrink cracks of bell pepper
Shrink cracks appear commonly around the fruit shoulders.
Rapid evaporation of condensed moisture on fruit surface causes shrink cracks.
Gradual change from day to night temperatures and night ventilation can prevent
this condition.
Figure 53: Shrink cracks of bell pepper
Figure 54: Fruit crooking of cucumber
Insect Pest and Disease Damage in Hydroponics
In hydroponics, soil borne diseases are virtually
eliminated. Certain common pests and diseases however, can affect these plants.
Vigilance and early identification are important in controlling such problems.
Keep the environment of the hydroponics plants clean and adopt correct cultural
practices such as supply of well-balanced nutrients to maintain the plants healthy.
Pests and diseases less affect healthy plants. Always start the cultivation
with healthy seedlings/planting materials.
Adopt Integrated Pest Management (IPM) strategies recommended
for vegetables. If necessary apply recommended chemicals to control insect pests
or diseases and always strictly adhere to recommended pre-harvest intervals.
In hydroponics all the essential nutrients are supplied
through the nutrient solution. If the solution is deficient or excess (toxic)
in any of these nutrients or the pH or the EC of the solution is beyond the
suitable range, the plants will show nutritional disorder symptoms.
These symptoms include changes in growth rate,
size of plants, leaf shape and colour, leaf thickness, stem colour, inter node
distance, nature of root system, etc. In addition, fruiting characteristics
may change. Although these external symptoms vary according to crops and varieties,
some common symptoms are described in table 5 and figures 55 to 62.
Table 5: Some common nutritional disorder visual symptoms exhibited by plants
|
|
|
|
Growth is restricted and plants are generally yellow (chlorotic) from lack of chlorophyll, especially olderleaves.Younger leaves remain green longer. Stems, petioles and lower leaf surfaces of tomato can turn purple. |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Table 5: Continued
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Figure 55: Calcium deficiency in strowberry Figure
59: Nitrogen deficiency in tomato
Figure 56: Iron deficiency in strowberry Figure
60: Zinc deficiency in strowberry
Figure 57: Manganese deficiency in tomato Figure
61: Magnesium deficiency in tomato
Figure 58: Iron deficiency in tomato Figure 62: Sulphur deficiency in strowberry
Advantages of Hydroponics/ Soil-less Culture• Land is not necessary. It can be practiced even in upstairs,
open spaces and in protected structures.
• Clean working environment. The grower will not have any direct contact with
soil.
• Low drudgery. No need of making beds, weeding, watering, etc.
• Continuous cultivation is possible.
• No soil borne diseases or nematode damage.
• Off-season production is possible.
• Vegetable cultivation can be done with leisure sense.
• Many plants were found to give yield early in hydroponics system.
• Higher yields possible with correct management practices.
• Easy to hire labour as hydroponics system is more attractive and easier than
cultivation in soil.
• No need of electricity, pumps, etc. for the non-circulating systems of solution
culture.
• Possibility of growing a wide variety of vegetable and flower crops including
Anthurium, marigolds, etc.
• Water wastage is reduced to minimum.
• Possible to grow plants and rooted cuttings free from soil particles for export.
• Higher initial capital expenditure. This will be further
high if the soil-less culture is combined with controlled environment agriculture.
• High degree of management skills is necessary for solution preparation, maintenance
of pH and EC, nutrient deficiency judgment and correction, ensuring aeration,
maintenance of favourable condition inside protected structures, etc.
• Considering the significantly high cost, the soil-less culture is limited
to high value crops of the area of cultivation.
• A large-scale cultivator may have to purchase instruments to measure pH and
EC of the nutrient solution.
• Energy inputs are necessary to run the system.
• Yields were found to decrease when temperature of the solution rises during
warm periods.
Crops to Grow with Hydroponics/ Soil-less Culture
A variety of crops can be grown using hydroponics/soil-less
culture. However, priority must be given to high-value crops depending on the
market situation.
Leafy vegetables -
Lettuce, Head lettuce, Kang kong, Gotukola
Vegetables
- Tomato, Egg Plant, Green bean, Beet, Winged bean, Capsicum, Bell pepper,
Cabbage, Cauliflower, cucumbers, melons, raddish
Fodder crops -
Sorghum, Alphalfa, Barley, Bermuda grass, Carpet grass
Cereals -
Rice, Maize
Condiments -
Parsley, Mint, Oregano, Sweet basil
Fruit crops -
Strawberry,
Flower/ornamental crops - Anthurium,
Merrygold, Coleus, roses, carnations, orchids, chrysanthemums,
Medicinal crops
- Alovera
Harvesting, Grading, Storage and Marketing
Harvesting
Harvesting at correct maturity will reduce post harvest
loses. One must know the age of the fruits or plants to correctly identify maturity.
Reports on crops may be maintained for this purpose. Harvest fruits by cutting
with a sharp knife with minimum damage to fruits and plant stem.
Figure 63: Some crops that can be hydroponically grown
Harvest bell pepper after they develop their standard colour.
For salads, harvests before the fruits reach full red ripen stage; when they
are at yellow-red stage. It is better to wear a pair of gloves while harvesting
and use disinfected knife or scissors.
At least some colour should be showing in tomato fruit before harvest. If the
stems are attached care should be taken during handling to avoid any cuts or
bruises.
Cucumbers must be harvested with no attached stem when they reach a uniform
diameter throughout the fruit length, but before any yellowing appears at the
blossom end. Harvest strawberry fruits when they begin to turn red.
Leafy vegetables must be harvested before they reach their full maturity. Select
the correct stage of maturity for ornamental plants and fruits depending on
the market requirements.
Grading
When the harvest is in fruit form, discard odd shaped,
damaged, or spotted fruits and grade according to their sizes into large, medium
and small size groups. It may be suitably labeled to indicate its quality (for
example, free of pesticides).
Storage
After grading, most vegetables must be stored in cool
dry place. Storing in large plastic containers with large holes for aeration
is advisable.
Marketing
Depending on the market requirement, produce can be
sold in small packing. They can be suitably labeled. The packing must have aeration
holes.
Figure 64: Packing of tomato for marketing
Submersible or ordinary water pumps, EC meter, pH meter are the essential equipment necessary to operate a circulating hydroponics. PVC pipes can be used as channels in these systems.
Water Pumps
Figure 65: A domestic water pump Figure
66: A submersible water pump
Figure 67: PVC pipe system for hydroponics
pH and EC Meters
Simple and portable EC and pH meters must be used to
monitor and maintain the EC and pH at correct levels.
Blowers
These devices help send airflow through the plants
so that plants shake and pollens are distributed to facilitate pollination inside
protected structures.
Figure 69: A simple blower Figure
68: Simple digital pH and EC meters
Pollinators
These simple electrical device vibrate the individual
plants when touch them so that pollination is facilitated inside the protected
structures.
Nurtimeter
In addition to the EC, this meter helps measure the
nutrient contents of the solution.
Figure 70: A nutri-meter