ABSTRACT
Although the elements essential for plants are the same, regardless of whether they are from sources in the soil or the nutrient solution, their original form may differ� In soil, these elements come from the break down of organic matter through microbial organisms and animal decomposition� Animals would be, for example, earthworms that consume organic matter of the humus of the soil and excrete simpler forms of organic compounds� These compounds are further decomposed into more simple compounds by the microorganisms� The end process is the release of inorganic elements into the soil water to form the soil solution that brings these essential minerals in contact with plant roots where they are absorbed� The elements must be in their charged atomic state (ions) to be taken up by plants� The other component of soil that is a source of minerals is the sand, silt, clay, and rocks that break down through weathering� Wind and water will break them into very fine particles that when in contact with the soil water will be released as ions, once again available to the plant roots�
In adding nutrients to soil, we supplement with composts, manures, peatlite mixes, perlite, fertilizers, and so on to also improve the structure of the soil (Figure 8�1)� Generally, with soil growing the choice of fertilizer depends on the plant and the results of a soil analysis� Normally, blends are used� Fertilizers have a guaranteed analysis that appears on their bags� All chemical and organic fertilizers have their guaranteed analysis on their label� For example, a common vegetable garden fertilizer is 5-10-5� This fertilizer contains 5 percent nitrogen, 10 percent phosphate (P2O5), and 5 percent potash (K2O)� The particular fertilizer should be chosen after a soil analysis� The laboratory doing the analysis will make recommendations as to the fertilizer components needed for your soil� The pH of the soil may be modified by the use of lime to raise it or sulfur to lower it� Most fertilizers used in soil gardening are available in granular and water-soluble forms� Granular fertilizers slowly release the plant nutrients to the soil water and therefore act slowly, but have the advantage of being long lasting� Water-soluble fertilizers are fast acting, but, move rapidly through the soil, so must be applied more frequently than granular forms�
In hydroponic culture, we grow in containers or some form of medium that is wrapped with plastic, such as “slabs” that are long, narrow, bags with the substrate� They generally measure 3 ft by 6-8″ wide by 4″ thick� These slabs will sit on return channels underneath that will collect the spent solution (leachate) and recycle it or drain it away from the growing area (Figure 8�2)� For this reason, because the nutrient
soluton does not just pass the root zone but is distributed precisely near the base of the plants with a drip irrigation system highly pure and soluble fertilizers are used� These highly soluble fertilizers insure that all of their elements are released to the water to form the nutrient solution� The nutrient solution is complete in containing all 13 essential elements in the correct concentratons, measured in parts per million (ppm) or milligrams per liter (mg/L), for optimum plant growth�
The sources of the plant nutrients must be highly soluble and of high purity� Hydroponic suppliers handle many blends of nutrient solution so that you may choose the best for your crop (Figure 8�3)� There are different formulations for different stages of plant growth, starting solution, initial vegetative growth, flowering stage, and fruit production� There are vegetable formulations as well as flower and ornamental ones�
Most prepared nutrients come in two components; “A” and “B�” A few are available as just one mixture� The use of a two part formulation is usually better to prevent any possible reaction from occuring among the various elemental components� Usually one will contain calcium, nitrogen, potassium, and iron� The other will have the rest of the elements, including the microelements� They are at concentrated levels when packaged or bottled, so cannot be mixed at those levels or they will react to form an insoluble hard substance, a precipitate� The precipitate cannot be re-dissolved in water� For example, if you mix concentrated calcium or iron with a sulfate, such as Epsom salts (magnesium sulfate) precipitation will result in an insoluble form of calcium sulfate or iron sulfate� Dissolve parts A and B separately in water to prevent any reaction� The ingredients of part A are normally calcium nitrate, potassium nitrate, and iron chelate� Part B may contain potassium nitrate, potassium sulfate, monopotassium phosphate, magnesium sulfate, and other sulfates of manganese, zinc, and copper� In addition, part B will have the remaining trace elements of boron, molybdenum, and chlorine�
If you wish to take on the challenge of making up your own nutrient formulations, that is discussed in the following chapter� As I mentioned above, the compounds you select to add the essential elements for the nutrient solution must be pure and highly soluble� The following is a list of recommended compounds for the solution makeup�
Calcium Nitrate: Molecular Formula: Ca(NO3)2 It is important to purchase “Greenhouse Grade” to avoid the presence of
a greasy plasticizer on lower grades� One source is called “YaraLiva” CALCINIT™ Greenhouse Grade, 15�5-0-0 with 19 percent calcium� It is a product of Norway�
Another brand of highly soluble calcium nitrate is “Haifa Cal GG�” This is also a greenhouse grade made by Haifa Chemicals Ltd�, Haifa, Israel, and manufactured in Slovakia�
This compound provides calcium (Ca) and nitrogen (N) for your plants� Potassium Nitrate: Molecular Formula: KNO3
Once again select a soluble grade of fine powder form� “Yara Krista K” is a brand of soluble potassium nitrate 13�7-0-46 coming from Chile by SQM Industrial SA�
This compound provides potassium (K) and nitrogen (N)� Magnesium Sulfate: Molecular Formula: MgSO4�7H2O
Highly soluble brands are a white crystalline powder; that is the heptahydrate (it has seven molecules of water attached as shown in the chemical formula)� It is commonly known as “Epsom salts�” It contains 9�8 percent magnesium (Mg) and 12�9 percent sulfur (S)� PQ Corporation in Pennsylvania produces it� This can also be purchased in small quantities, very pure form at pharmacies�
Monopotassium Phosphate: Molecular Formula: KH2PO4 A good highly soluble brand is Haifa Chemicals Ltd in Israel� The guar-
anteed analysis is 0-52-34� This compound gives potassium (K) and phosphorous (P)�
Potassium Sulfate (Sulfate of Potash): Molecular Formula: K2SO4 “Champion” water soluble grade (“crystalline”) is produced by SQM in the
United States� Its analysis is 0-0-51-17 where the last figure indicates 17 percent sulfur�
It supplies potassium and sulfur for the plants� Iron Chelate: Molecular Name: Sodium Ferric Diethylenetriamine Pentaacetate
(Fe-DTPA) This is termed “Sprint 330” and made by Becker Underwood, Inc�, in the
United States� It has 10 percent elemental iron (Fe)� Iron is a minor element, but is required in greater amounts than other minor
elements� The plant needs may vary from 2�0 to 5�0 ppm� Other minor elements are at optimum levels less than one part per million�
Manganese Sulfate (MnSO4�4H2O) or Manganese Chelate (MnEDTA)� Either of these compounds is a source of manganese� If your water is alka-
line, the chelate is a better source because the chelating agent will keep the manganese available to the plant�
Zinc Sulfate: Molecular Formula: ZnSO4�7H2O This product is very soluble if the white powder form is used� It adds zinc
(Zn) to the nutrient solution� Copper Sulfate: Molecular Formula: CuSO4�5H2O
This is also termed bluestone due to its blue crystals� It is highly soluble in providing copper (Cu)�
Boric Acid: Molecular Formula: H3BO3 Boric acid, also called Boracic acid, is used as an antiseptic for minor burns
or cuts and as an eye rinse� This provides boron (B)� Boric acid is available at a pharmacy�
Ammonium Molybdate: Molecular Formula: (NH4)6Mo7O24 Sodium Molybdate: Molecular Formula: Na2MoO4
Either of these is highly soluble in supplying molybdenum (Mo)�
Note: With the minor elements, except iron, use very small amounts so purchase them as laboratory reagents in small quantities at most laboratory suppliers� They will be very pure and soluble�
Calculations to develop a nutrient formulation and how to make a nutrient solution with the formulation is discussed in Chapter 9�
As I mentioned earlier, you do not need to get this involved in making up your own formulation and storing all of these compounds� It is far simpler to purchase a ready-made formulation from a hydroponic supplier� However, as with most hobbies, you may wish to explore more technical details of growing your crops and experimenting with formulations to find the most optimum to maximize yields� Just enjoy the success of growing hydroponically at a level that suits you best!
