Water Management in the Soilless Culture

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  • 8/13/2019 Water Management in the Soilless Culture




    Water Management in the Soilless Culture

    Arghya Narendra Dianastya





  • 8/13/2019 Water Management in the Soilless Culture



    Hydroponics is a technology for growing plants in nutrient solutions (water

    containing fertilizers) with or without the use of an artificial medium to provide mechanical

    support. Liquid hydroponic systems have no other supporting medium for the plant roots:

    aggregate systems have a solid medium of support. Because of the higher control over

    nutrients, hydroponically grown plants generally have a much higher yield than similar plants

    grown in soil.

    EC and pH measurment of chemical solution is very important. The pH is a parameter

    that measures the acidity or alkalinity of a solution. This value indicates the relationship

    between the concentration of free ions H+ and OH- present in a solution and ranges between0 and 14. The concentration and pH of nutrient solution must be measured and monitored

    during growing period. These method is done using portable EC and pH meter.

    An important feature of the nutrient solutions is that they must contain the ions in

    solution and in chemical forms that can be absorbed by plants, so in hydroponic systems the

    plant productivity is closely related with to nutrient uptake and the pH regulation. Each

    nutrient shows differential responses to changes in pH of the nutrient solution.

    Nutrient solution has tobe make by using water. Water is very essential for soiless

    culture because all nutrients must be solved with water tobe uptaken by plant. Water quality

    must be clean, free from diseases, chemical residues, organic and inorganic materials.Making

    suitable water for hydroponic can be done by puryfying the water. Water treatments consist

    of purification by using water filters, pH adjustment, and sterilization by using oxidative

    agents such as chlorine or UV ray.

    The impurity in the water can be removed by water filters. The best way to purify

    water is using Reverse Osmosis. the RO- water will be cleaned from both ion and cation. The

    EC of the water using Reverse Osmosis also become 0.05 mS cm-1. The addition of acids or

    alkalis to nutrient solutions also the most common and practical means to adjust pH, and can

    be easily automated. There are ways to minimize pH variations and they are worth some

    consideration. Most plants are able to absorb either nitrate (NO3-) or ammonium (NH4+) or

    both. NH4+ as the sole source of nitrogen or in excess is deleterious to the growth of many

    plant species. Some plants yield better when supplied with a mixture of NH4+ (ammonium)

    and NO3- (nitrate) compared to NO3- alone. A combination of NH4+ and NO3- can be used

    to buffer against changes in pH.

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    1. To Familiar student with the purification of water to be used in soiless culture

    2. To Familiar students with the mantenance of water filter

    3. To Familiar students with pH adjustment of water in soilless culture

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    1. For excercise 1, Draws a picture of RO-filter and labels major components and reportsits operation and maintenance

    2. For excercise 2, report the pH adjusment by acid solution using the provided tablesand graphs and discuss the following points.

    a. Comparison of the efficiency of different acid solutionb. The amount of acid solution to lower pH from 8 to 7 and from 7 to 5 are the

    same or not.

    c. How does EC of water changing after each pH adjustment3.

    For excercise 3, write the report of the result from table 3. Discuss how much theactual total acid solution to be used for adjusting pH of water on the DRFT table and

    for how long. Compare the actual amount of acid solution used and the amount from

    the calculation.

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    Exercise I

    1.1 Picture of Reverse Osmosis

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    1.2 Basic components common to all Reverse Osmosis Systems:

    1. Cold Water Line Valve: Valve that fits onto the cold water supply line. The valve has atube that attaches to the inlet side of the RO pre filter. This is the water source for the RO


    2. Pre-Filter (s): Water from the cold water supply line enters the Reverse Osmosis PreFilter first. There may be more than one pre-filter used in a Reverse Osmosis system. The

    most commonly used pre-filters are sediment filters. These are used to remove sand silt,

    dirt and other sediment. Additionally, carbon filters may be used to remove chlorine,

    which can have a negative effect on TFC (thin film composite) & TFM (thin film material)

    membranes. Carbon pre filters are not used if the RO system contains a CTA (cellulose tri-

    acetate) membrane.

    3. Reverse Osmosis Membrane: The Reverse Osmosis Membrane is the heart of thesystem. The most commonly used is a spiral wound of which there are two options: the

    CTA (cellulose tri-acetate), which is chlorine tolerant, and the TFC/TFM (thin film

    composite/material), which is not chlorine tolerant.

    4. Post filter (s): After the water leaves the RO storage tank, but before going to the ROfaucet, the product water goes through the post filter (s). The post filter (s) is generally

    carbon (either in granular or carbon block form). Any remaining tastes and odors are

    removed from the product water by post filtration.

    5. Automatic Shut Off Valve (SOV): To conserve water, the RO system has an automaticshutoff valve. When the storage tank is full (this may vary based upon the incoming water

    pressure) this valve stops any further water from entering the membrane, thereby stopping

    water production. By shutting off the flow this valve also stops water from flowing to the

    drain. Once water is drawn from the RO drinking water faucet, the pressure in the tank

    drops and the shut off valves opens, allowing water to flow to the membrane and waste-

    water (water containing contaminants) to flow down the drain.

    6. Check Valve: A check valve is located in the outlet end of the RO membrane housing.The check valve prevents the backward flow or product water from the RO storage tank. A

    backward flow could rupture the RO membrane.

    7. Flow Restrictor: Water flow through the RO membrane is regulated by a flow control.There are many different styles of flow controls. This device maintains the flow rate

    required to obtain the highest quality drinking water (based on the gallon capacity of the

    membrane). It also helps maintain pressure on the inlet side of the membrane. Without the

    flow control very little drinking water would be produced because all the incoming tap

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    water would take the path of least resistance and simply flow down the drain line. The

    flow control is located in the RO drain line tubing.

    8. Storage Tank: The standard RO storage tank holds up to 2.5 gallons of water. A bladderinside the tank keeps water pressurized in the tank when it is full.

    9. Drain line: This line runs from the outlet end of the Reverse Osmosis membrane housingto the drain. This line is used to dispose of the impurities and contaminants found in the

    incoming water source (tap water). The flow control is also installed in this line.

    1.3 Operation of Reverse Osmosis Machine

    Reverse osmosis is a complicated process which uses a membrane under pressure to

    separate relatively pure water (or other solvent) from a less pure solution. When two aqueous

    solutions of different concentrations are separated by a semi-permeable membrane, water

    passes through the membrane in the direction of the more concentrated solution as a result of

    osmotic pressure. If enough counter pressure is applied to the concentrated solution to

    overcome the osmotic pressure, the flow of water will be reversed.

    Water molecules can form hydrogen bonds in the reverse osmosis membrane and fit

    into the membrane matrix. The water molecules that enter the membrane by hydrogen

    bonding can be pushed through under pressure. Most organic substances with a molecular

    weight over 100 are sieved out, i.e., oils, pyrogens and particulates including bacteria and

    viruses. Salt ions, on the other hand, are rejected by a mechanism related to the valence of the

    ion. Ions are repelled by dielectric interactions; ions with higher charges are repelled to a

    greater distance from the membrane surface. The nominal rejection ratio of common ionic

    salts is 85 - 98%.

    The majority of the commercially manufactured Reverse O smosis (RO) membranes

    are usually made from cellulose acetate, polysulfonate, and polyamide. The membrane

    consists of a skin about 0.25 microns and a support layer about 100 microns. The skin is the

    active barrier and primarily allows water to pass through.

    1.4 Maintenance of RO Machine

    Reverse osmosis system maintenance consists of nothing more than filter and

    membrane replacement on a routine schedule. Beside that, reverse osmosis machine need to

    maintain the power of the water pump as well.

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    Exercise II

    2.1 Comparison of the efficeincy of different acid solution

    2.1.1 General Knowledge

    pH si very important in hydroponic system. When the pH is not at the proper level

    the plant will lose its ability to absorb some of the essential elements required for healthy

    growth. For all plants there is a particular pH level that will produce optimum results. This

    pH level will vary from plant to plant, but in general most plants prefer a slightly acid

    growing environment (between 5.5-6.0), although most plants can still survive in an

    environment with a pH of between 5.0 and 7.5.

    When pH rises above 6.5 some of the nutrients and micro-nutrients begin to

    precipitate out of solution and can stick to the walls of the reservoir and growing chambers.

    For example: Iron will be about half precipitated at the pH level of 7.3 and at about 8.0 there

    is virtually no iron left in solution at all. In order for your plants to use the nutrients they must

    be dissolved in the solution. Once the nutrients have precipitated out of solution your plants

    can no longer absorb them and will suffer deficiency and death if left uncorrected. Some

    nutrients will precipitate out of solution when the pH drops also.

    There are some example the optimum pH range for hydroponic crops and nutrient

    available range :

    (From Hydroponic Food


    by Howard M. Resh

    Woodbridge Press, 1987)


    This chart is for soiless (hydroponic) gardening only


    does not apply to organic or dirt gardening.

    Plant pH Range































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    Usually, Tap water used in hydroponic has pH above 7 or alkaline. The efficiency of

    pH lowering depends on the power of the acid solutions and their concentrations. Strong acid

    such as H2SO4, HNO3, HCl has more power to lower th pH than waker acid such as H3PO4.

    This is the example of strong and weak acid solutions :

    2.1.2 Table

    The pH changing as the effect of sulfuric acid, HNO3, and phosporic acid solution with

    the equal concentration of 1%



    H2SO4 (1%) HNO3 (1%) H3PO4 (1%)

    pH EC


    pH EC


    pH EC


    0 8 0.36 7.6 0.31 7.6 0.25

    0.5 7.3 0.37 7.5 0.31 7.5 0.27

    1 7.1 0.37 7.0 0.32 7.0 0.30

    1.5 7.0 0.37 7.0 0.32 6.9 0.30

    2 6.8 0.37 6.8 0.32 6.7 0.30

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    2.5 6.6 0.38 6.7 0.32 6.6 0.30

    3 6.6 0.38 6.6 0.32 6.5 0.29

    2.1.3 ResultIt can be seen in the table of exercise that H2SO4 and HNO3 give the most dramatical

    change in pH of the water. The H2SO4 which is the strongest one of the solution gives the

    highest changed of pH of water from 8 to 7.3 with 0.5 ml concentration only. H3PO4 is the

    lowest in the term of efficiency with very slow to pH changed.

    Sulfuric acid (alternative spelling sulphuric acid) is a highlycorrosivestrongmineral

    acid with the molecular formula H2SO4. But, the strong acid as sulfuric acid (H2SO4) is

    prohibited since they give extra S or sulphur that can be toxic to plants if the accumulative

    concentration is too high.

    The main problem with too much phosphorus is eutrophication resulting in excessive

    growth of plants and algae in the water. This can seriously limit the use of the water for

    drinking, industry, fishing, or recreation. Pollution reduction may not be simply a direct

    economic problem for the farmer, but a responsibility that extends beyond the farm fence.

    2.2 The amount of acid solution to lower pH from 8 to 7 and from 7 to 5

    Volume (ml) pH EC (mS/cm)

    0 7.7 0.31

    1 7.2 0.32

    2 7.0 0.33

    3 6.8 0.32

    4 6.6 0.33

    5 6.5 0.33

    6 6.3 0.34

    7 6.3 0.34

    8 6 0.34

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    2.2.2 Discussion

    We can see from the result that the pH adjustment by acid solution to lower pH from

    8 to 7 and from 7 to 5 are different. Using HNO3 as a solution, to make pH from 8 to 7 just

    take 3 ml of HNO3 but to make pH from 7 to 5 takes 10 ml of HNO3. This is because HNO3

    can be used as a buffer for solution. A buffer is an aqueous solution consisting of a mixture of

    aweak acid and itsconjugate base or aweak base and itsconjugate acid.ItspH changes very

    little when a small amount ofstrong acid orbase is added to it and thus it is used to prevent

    changes in the pH of a solution. Buffer solutions are used as a means of keeping pH at a

    nearly constant value in a wide variety of chemical applications.

    Even HNO3 is a strong acid, but ionized nitric acid w...


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