• Hydroponics (Aquaculture)
• From the Greek: Hydro = water + Ponos = labor.
• Not commonly used for growing nursery crops, but it teaches lessons regarding plant growth requirements.
• Sachs (1860) & Knop (1861 - 1865) worked on how to identify essential elements by including and excluding elements from water in which plants were growing.
• The first person to use hydroponics outside of the lab and to realize its commercial potential was Dr. W. F. Gericke California (1929).
• Hydroponics was used during WWII for growing fresh vegetables for the US troops in the Pacific.
• Roots require the following things which must be supplied by any solution or media:
  • Water -- Obviously readily available in a hydroponic medium.
  • Nutrients -- Must be added as salts to the water
  • Air -- Must be somehow added to the solution, bubbled through or otherwise.
  • Support -- Water does not lend enough support to plants - support must come from elsewhere.
• Plants grown hydroponically can be grown in humid air, in an inert substance with water around it, or in water infused with air.

Nutrients added

• In Water Culture all nutrients need to be added, in aggregate culture less nutrients may need to be added.
• Some major problems may occur when adding nutrients.
  • Nutrients not adequately soluble.
  • Acid or basic reaction - salts need to be added.
  • Some elements react with others and drop out of solution.
  • Different plants have different nutrient requirements - all hydroponic solutions are not adequate for all plants.
  • Nutrient solutions need to be changed as often as every week during heavy growth stages.
  • This mix can be changed and adapted in a variety of ways to increase or decrease the concentration of any element.
  • Many salts other than those listed can be used and other elements can be added to test possible effects.
  • pH is generally not as important in nutrient culture as it is in a field or container. This does not mean that it is unimportant!
  • A pH below 4.5 or above 9 can directly damage plant roots.
  • A pH of above 7 will cause elements including Fe, Mn, PO4, Ca and Mg to precipitate out of solution, making them unavailable.
  • As a rule, if a plant prefers an acid soil then it will also prefer an acid hydroponic solution.
  • Adding diluted Nitric or Sulfuric acid drop-wise will decrease pH (use a pH meter to determine pH).
  • Adding small quantities of lime will increase pH, but may bind other nutrients.
• Here is an example of a mix of salts that is used by the USDA and is known as Hoaglands Solution which is added to create a hydroponic solution.

Major Elements	(g/1000 L) in water
Calcium Nitrate	1181
Potassium Nitrate	505.5
Monopotassium Phosphate	136.1
Magnesium Sulfate	493

*To this add a micronutrient solution (1 L per 1000 L of volume) containing the following:

Minor Elements	(g/1 L) of solution
Boric Acid	2.86
Manganous Chloride	1.81
Zinc Sulfate	0.22
Copper Sulfate	0.08
Molybdic Acid	0.02
Fe Sequestrene	10

*This is only one of many possible nutrient mixes.

General Types of Hydroponic Production include:

• Water Culture
  • Water and Nutrients - how are they delivered?
    • Containers hold plants whose roots are immersed in nutrient solution
      • Solution must be changed frequently or a large amount of solution must be cycled to maintain a given concentration of nutrients.
    • Nutrients are dissolved in water which is brought to roots
  • Air - how is it delivered
    • Air is bubbled through the container
    • Nutrient solution is aerated before it reaches the roots.
    • Water is misted onto plants
  • Stability - stems need to be kept stable
    • Plant may be held up by a wire
    • Plant may be held up by a sponge around the orifice of the opening made for the plant.
      • In container systems opaque containers are not used so that light does not get inside - this prevents the growth of algae and other organisms
  • Examples
    • Plants growing in air with a mist system.
    • Plants grown in buckets with nutrient solution and an air hose
    • Nutrient Film Technique -- Nutrient rich water is run along a series of troughs that contain plants. This constant flow allows nutrients to be more available and allows aeration.
• Aggregate culture.
  • Water and Nutrients
    • Generally nutrient solutions are pumped into an inert substance holding the plants.
    • Solution can be changed or cycled, just as with water culture.
  • Support
    • The inert substance surrounding the roots provides support
    • The substance surrounding the roots may be complemented by a support wire.
  • Air
    • Water surrounding root area is drained - porous material holds sufficient air and moisture for plant growth until next cycle.
  •                         Examples
  •                                 Perlite
  •                                 Sand
  •                                 Gravel
  •                                 Rockwool
  •                                 Sawdust
• Some Mathematical Problems
  • To use a hydroponics system you must be versed in how to convert units. For example, how many ppm. (parts per million) of calcium are there in that 1 M (molar) solution of calcium nitrate?
  • Calculations which you will need to be able to do include the following
  • Calculate molarity
    • M is a standard unit of measurement that standardizes the amount of a compound added to a solvent by considering the molecular weight of the compound.
    • 1 M of a solution is actually nothing more than molecular weight of the compound expressed as grams in 1 L of water. Thus 1 M of NaCl is 58.4g of NaCl in 1 L. of water.
  • Calculate ppm.
    • One of the most useful facts which you will learn in this class is that 1 ppm is equal to 1 mg of a compound per liter of water.
    • If there are 15 mg of NaCl in a 1 liter of water how many ppm of Na are in this liter of water?
      • What percent of NaCl is Na?
        • Find the molecular weight of Na (= 23.0) and the molecular weight of NaCl (= 58.4)
        • Divide 23.0 by 58.4 to get the ratio of Na in NaCl (=0.394).
        • Multiply 0.394 by 15 mg = 5.91 mg of Na in that 1 L solution
        • Since 1 mg of a compound = 1 ppm there are 5.91 ppm Na in that water

 Some Example Problems

1. You have a 1 L container filled with a 1 M solution of KCl.  What elements are in the solution?
2. How many ppm K are in the solution?
3. How much of this solution will need to be added to 8 L of water to make of a 300 ppm K solution?
4. If you have 500 ppm Na in a solution containing NaCl, how many ppm NaCl do you have?
5. How many grams of H₂PO₄ are there in 5 L of a 1 M solution? How many ppm P?

   Visual Representations of Some Hydroponic Techniques: