Hydrophonics

What is hydroponics?

Hydroponics is the growing of plants without soil.

What does soil do for the plant?

1. Nutrients

2. Water

3. Aeration

4. Anchorage

What is part of a typical hydroponic system

1. Reservoir

2. Nutrient solution

3. Grow tray

4. Pump

5. Growth medium

6. Roots

What replaces soil in hydroponics?

Inert media → growth media such as

1. Perlite

2. Vermiculite

3. Horicultural rockwool

4. sand

5. Fired clay pebbles

What may happen to rockwool in hydroponics?

Algae growth → turns it green

Why is it bad to use an unopaque tank for hydroponics? (e.g. aquarium tank)

With glass sides, sunlight will pass through into the nutrient solution, and algae will proliferate, competing with the plants for nutrients and oxygen.

What does this growing media do?

Provide porous and well aerated substrate for the anchorage of plant roots

Evaluate the differences between soil and hydroponics in terms of providing physical support and manpower needed

Soil

• Physical support for plant roots (+)

• Acting as a buffer

Hydroponics

• various types of growing media provide porous and well-aerated substrate for the anchorage of plant roots

• In the absence of soil, the pH value of the nutrient solution must be checked regularly.

What are the types of systems in hydroponics

1. Open system

2. Closed system

What is a open system?

A system in which fresh nutrient solution is introduced for each irrigation cycle

What are the types of open systems?

1. Drip system

2. Root dipping technique

Explain the drip system + explain what must be needed

It delivers the nutrient solution to the plants via a drip pump

To keep nutrient balance in the root zone of the plants, an ADEQUATE run-off must be maintained in open hydroponic systems.

Explain the root dipping technique + explain what must be needed to sustain this technique

Nutrient solution is placed in a container and a board with holes for pots is placed over it. The plants are grown in some growing medium in pots, and their roots extend into the nutrient solution once the pots are placed into the holes of the board.

There must be adequate air space above the nutrient solution, and only the bottom one-third of the root system dips into the solution to ensure adequate aeration for the roots.

Why is it not advisable to fill the box to the brim with nutrient solution using the root dipping technique?

He should not have filled up the box to the brim with nutrient solution as there must be space for adequate aeration for the plants.

Why is this open system not advantageous?

Replacement of the nutrient solution after each harvest is costly;

runoff from the discarded solution is likely to cause eutrophication in bodies of water in the environment

What are the advantages and disadvantages of the open system

Advantages:

1. There is no need to incur cost in setting up a pump-system to re-circulate the nutrient solution

2. The concentration of nutrients and pH of solution need not be checked if a fresh solution is always used; this saves on manpower

Disadvantages:

1. The cost of regular replacement of the nutrient solution is high

2. The run-off contaminates the environment as the used nutrient solution can still cause eutrophication in closed water bodies; to process this involves extra cost.

What is a closed system

System in which the same nutrient solution is re-circulated and the nutrient concentrations, together with the pH, are monitored and adjusted regularly

What are the advantages and disadvantages of a closed system

Advantages:

1. This system recycles nutrient solutions as effectively as possible; this reduces cost of replacing nutrient solutions

2. There is no contamination of the environment as the solution is recirculated within the system

Disadvantages:

1. The nutrient solution has to be sampled and analyzed at least once a week to ensure that the nutrient balance is maintained; this is labour intensive

2. A pump system is needed to re-circulate and oxygenate the nutrient solution (incur higher cost)

What are some examples of a closed system

Nutrient Film Technique

Deep Flow Technique

Aeroponics

What is nutrient film technique (NFT)

There is a continuous thin film of nutrient solution flowing over the roots. This provides aeration and nutrients. Plants are grown in channels placed on a gentle slope, and a pump re-circulates the nutrient solution.

What are the advantages and disadvantages of the NFT system

Advantages:

1. Lower consumption of nutrient solution

2. Absence of growth medium saves cost and makes it easier to check the health of roots

3. It is environmentally friendly: minimal potential for localised groundwater contamination

Disadvantages:

1. The pump must not fail, as even a short period of the pump not functioning can cause plant death

2. It is not suitable for plants with large tap-root systems as the roots clog up the trough and impede flow of nutrients

What is the deep flow technique (DFT)

The plants float on a raft (typically a sheet of foam plastics such as polystyrene) in a shallow tank less than 0.3m deep. The tank, or pond, is filled with nutrient solution, and the plant roots hang down into the solution. The nutrient solution is monitored, oxygenated, replenished and recirculated as required.

What is the advantages of a DFT system?

1. Provides significantly greater buffering than other hydroponic techniques (e.g. NFT)

Changes of nutrient level, pH, temperature, and dissolved oxygen (DO) concentration, are significantly damped.

2. Ponds can also be used as material movement with minimal mechanisation or physical effort.

Explain aeroponics (high tech)

System whereby roots are kept in an environment saturated with a mist of nutrient solution.

What is not needed for aeroponics?

No substrate is needed, and involves growing plants with their roots suspended in a growth chamber in which fine mist of atomized nutrients is periodically sprayed.

(nutrients are re-circulated, hence it is a closed system)

What are the advantages of aeroponics and disadvantages of aeroponics

Advantages:

1. Roots are well-aerated, leading to faster plant growth

2. Uses 65% less water and only 25% of the nutrient input compared with hydroponics

Disadvantages:

1. Dependence on the system — a typical aeroponic system is made up of high-pressure pumps, sprinklers and timers. If any of these break down, the plants can be damaged or killed easily

2. The root chamber must be disinfected, or diseases may affect the roots.

How can we measure the total concentration of the solution?

Using Electrical conductivity and pH

What does electrical conductivity (EC) measure?

Strength of nutrient solution, measured using an EC meter

What is the limitation of the EC

Indicates only the total concentration of the solution and not the individual nutrient components.

What is the ideal range for hydroponics for EC?

1.5 to 2.5 dS/m

What will happen if there is a higher EC and a lower EC?

Prevent nutrient absorption due to osmotic pressure and a lower EC will severely affect plant health and yield due to lack of nutrients

Why high EC prevents nutrient absorption

High concentration of nutrients → low water potential

Low nutrient absorption because mineral salts are dissolved in water, affecting active transport due to poor osmosis.

What is pH?

Measure of the acidity or alkalinity of a solution

What does it determine? (pH)

It determines the availability of essential plant elements

What is the optimum pH for a hydroponic nutrient solution?

5.8 and 6.5

What does too high or low of a pH prevent?

>6.5

Fe and Zn less available

<5.8

Ca and Mg less available

Advantages of hydroponics compared to soil farming:

1. Easier to sow and harvest crops compared to soil farming; although still labour intensive, the work is not so heavy, and technology can be put to good use in some parts of the operation.

2. In closed systems, water stays in the system and can be re-circulated, this is useful in drier areas

3. More intensive use of space leads to high-density of plants and maximum crop yield

4. There is a high degree of control over the nutrients used, and this reduces costs

5. No nutrient is released into the environment in closed systems; eutrophication is minimised

6. No limitation in terms of fertility in soil, as the growing locations can be extended to areas unsuitable for soil farming

7. In an controlled environment, crops can be grown out of season or in unsuitable climates

Disadvantages of hydroponics compared to soil farming

1. Without soil as a buffer, any failure to the hydroponic system leads to rapid plant death

2. pH and EC values need to be checked regularly in closed systems; this requires manpower

3. Plants are susceptible to pathogens without the protection provided by soil microorganisms

4. Aeration can be a problem and plants can become water-logged (overcome by aeroponics)

Difference between open and closed systems

Open system → nutrient solution is not re-used

Closed system → nutrient solution is re-circulated

How does an air stone aerate the nutrient solution?

The air stone reduces the size of the air bubbles from the air pump, and this allows for faster dissolving of the oxygen in the solution.