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    Is Hydroponics Really that Easy?Petrus Langenhoven, Ph.D.

    Horticulture and Hydroponics Crops SpecialistJanuary 5, 2017

  • Outline


    What is Hydroponics? Container Media/Substrates Nutrient Solution Management

    Electrical Conductivity (EC) pH Alkalinity and control

    Irrigation Water Chemical Quality Greenhouse Irrigation Water Quality


    Nutritional Disorders Irrigation Water Biological Quality

    Monitoring Biological Quality of Irrigation Water

    Hype Around Organic Hydroponics

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    What is Hydroponics?

  • What is Hydroponics?


    The word hydroponics technically means working water, stemming from the Latin words "hydro" meaning water, and "ponos" meaning labor.

    Hydroponics is a subset of hydroculture and is a method of growing plants using mineral nutrient solutions, in water, without soil.

    Two types of hydroponics, solution culture and medium culture. Solution culture types (only solution for roots)

    Continuous flow solution culture, Nutrient Film Technique (Dr Alan Cooper, 1960s) Aeroponics

    Medium culture types (solid medium for roots, sub- or top irrigated, and in a container) Ebb and Flow (or flood and drain) sub-irrigation Run to waste (drain to waste) Deep water culture, plant roots suspended in nutrient solution Passive sub-irrigation, inert porous medium transports water and nutrients by capillary action. Pot sits in shallow

    solution or on a capillary mat saturated with nutrient solution.

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    Photos: Petrus Langenhoven

  • Main Characteristics of Various Growing Systems


    Source:Pardossi, A. et al., 2011. Fertigation and substrate management in closed systems

  • Open versus Closed Soilless Systems


    Source:Pardossi, A. et al., 2011. Fertigation and substrate management in closed systems

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    2014/15 season

    100.6 kgm-2 = 20.6 lbft-2or1006 tonha-1 = 449 US tonsacre-1or1006 tonha-1 = 897,352 lbsacre-1

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    Container Media / Substrates

  • Characteristics of an Ideal Container Substrate


    Generally growers select a substrate based on its availability and cost, as well as local experienceDrain fraction of at least 20 25% is used to prevent root zone salinization Adequate mechanical properties to guarantee plant stability Low bulk density; bulk density lower than 900 kgm3 and maybe as low as 80-120 kgm3 (light weight) High total porosity (70-90%), sum of macropores and micropores. Good water-holding capacity (50-65%). Available

    water (>30%). Air capacity (10-20%). Good aeration and drainage High permeability to air and water. Even distribution of air and water to sustain root activity pH of between 5.4 and 6.6 (dolomitic or calcitic limestone can be added to adjust pH) Low soluble salts content Chemically inert High cation exchange capacity (CEC), capacity of substrate to hold positively charged ions; ideal level of about 6-15 meq

    per 100 cc Ability to maintain the original characteristics during cultivation Absence of pathogens and pests Availability in standardized and uniform batches

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    Popular Container Media/SubstratesInorganic Media

    Organic MediaNatural Synthetic

    Sand Foam mats (Polyurethane) Sawdust

    Gravel Polystyrene Foam Composted Pine Bark

    Rockwool Oasis (Plastic Foam) Wood chips

    Glasswool Hydrogel Sphagnum Peat moss

    Perlite Biostrate Felt (Biobased Product) Coir (Coconut Peat/Fiber)

    Vermiculite Rice Hulls


    Expanded Clay


    Volcanic Tuff

  • pH of Different Media | Cation Exchange Capacity


    CEC - Capacity to hold and exchange mineral nutrients

  • Rockwool Perlite


    60% diabase (form of basalt rock, dolerite), 20% limestone, and 20% coke

    Melted at 2912F, spun at high speed into thin fibers

    Heated with phenolic resin and wetting agent to bind them together and lower the natural hydrophobicity of the material. Pressed into slabs

    Characteristics: Low bulk density and high porosity High water-holding capacity (80%) and good

    aeration Chemically inert with pH 6.0 to 6.5 No CEC or buffering capacity Dissolve at low pH, below 5.0 Reusable. Can last for up to 2 seasons

    Naturally occurring, nonrenewable, inorganic, siliceous volcanic rock

    Grinded and popped at 1800F. Expands to between 4 and 20 times larger

    Characteristics: Lightweight, sterile, white, porous aggregate Finished product is a closed cell that does

    not absorb water. Water will adhere to surface

    Usually included in mixture to improve drainage or increase aeration

    Neutral pH of between 6.5 and 7.5 Low CEC Chemically inert

  • Vermiculite Coconut Coir


    Its a mica-like, silicate mineral Contains mineral water between ore plates When heated at 1832F, ore plates move

    apart into an open, accordion-like structure Characteristics:

    Very light, high water retention and good aeration Low bulk density pH value is 7 to 7.5, and low EC Low pH can release Al into the solution Has a permanent negative electrical charge, and

    therefore CEC is high High nutrient content (K, Ca and Mg) Used as component of mixes and in propagation

    Coconut fiber / dust is an agricultural waste product derived from the husk of coconut fruit

    Alternative to peat moss and bark Composted for 4 months Characteristics:

    Can have high amounts of salts Water and air content varies according to texture

    components More fiber High air and low water content More peat a lot of water and little air

    Coir is hydrophilic, disburse evenly over the surface of fibers

    Higher pH than peat moss, pH is 5 to 6 Not inert and can store lots of nutrients, high CEC Require more Ca, S, Cu and Fe than peat moss. Greater N-

    immobilization than peat moss May contain excessive levels of K, Na and Cl. Soak and rinse

    well before use Use for up to 2 - 3 years

  • Composted or Aged Pine Bark Sphagnum Peat Moss


    Partially decomposed sphagnum moss, predominantly from Canada

    Available in different colors, indicate degree of decomposition

    Light-colored peat, larger particles and limited decomposition. Provides excellent aeration and decompose faster than black peat

    Black peat is highly decomposed, physical properties vary greatly

    Characteristics: High water-holding capacity High air capacity Naturally acidic with pH value between 3.0 to 4.0 Low nutrient content, but high CEC Naturally hydrophobic when dry Shrinkage results after water evaporates from pot

    Used in combination with peat for structure

    Predominant substrate in nursery industry

    Screened and aged (4-6weeks) Young bark decomposes more rapidly Bark should have little to no white

    wood Low bulk density High CEC

  • Summary of Different Chemical and Physical Properties of Some Common Materials Used to Create Growing Media


    Source: Wilkinson, K.M. et al., 2014. Tropical Nursery Manual

  • Examples of Common Substrate recipes Growers can Formulate to Produce Greenhouse and Nursery Crops


    Source: Owen, W.G. and R.G. Lopez, 2015. Purdue Extension Pub. HO-255-W. Evaluating container substrates and their components

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    Nutrient Solution Management

  • EC


    Units may be confusing1 mmhocm-1

    1 dSm-11 mScm-1

    10 mSdm-1100 mSm-1

    1000 Scm-1







    EC reading is impacted by temperature

    Temp (F) Temp (C) EC (mScm-1)

    59 15 1.62

    68 20 1.80

    77 25 2.00

    86 30 2.20

    Plus micro-nutrients

    Electrical Conductivity (EC), depends on how many charged particles are present in the solution. Measure of how well a solution or substrate conducts electricity

  • What are the Effects of Salt Stress (high EC) on Plants?


    Osmotic Loss of osmotic gradient for water absorption Worst case scenario: Results in wilting even though the substrate is moist Prolonged stress may result in reduced growth (shorter internodes and smaller leaves); even without wilting

    Toxic concentrations of ions Excess absorption of sodium and chloride Excess absorption of micronutrients such as boron, manganese, iron

    Carbonate and bicarbonate High pH will impact solubility of nutrients Over time pH of container substrate will increase Precipitation of calcium and magnesium

    Nutrient antagonisms Absorption of one nutrient might be limited by excess concentrations of another

    Excessive in Media Low Tissue Level

    NH4, Na, K, Ca, Mg Na, K, Ca, or Mg

    PO4 Zn or Fe

    Ca B

    Cl NO3Source: Paul Nelson

  • pH scale is logarithmic. Value will not decrease linearly when acid is added or increase linearly when basic is added


    The logarithmic scale of pH means that as pH increases, the H+ concentration will decrease by a power of 10. Thus at a pH of 0, H+ has a concentration of 1 M. At a pH of 7, this decreases to 0.0000001 M. At a pH of 14, there is only 0.00000000000001 M H+


    ce: F




    of E



    tal M




    Half of all nutritional disorders can be attributed to pH-related problems

    pH affects nutrient solubility

    Only dissolved nutrients are taken up by roots

  • Optimal nutrient availability in hydroponic nutrient solution at pH