SESSION 3: Plant Nutrients, Mixing and Testing Solutions
Water-Soluble Minerals (Nutrients in Solution)
A hydroponic gardener uses minerals that are water soluble and ready to be taken up by the plant roots. Scientists and researchers have determined exactly what minerals a plant needs and in what quantities. A large number of hydroponic nutrient formulas have been developed and, although some have better results than others, there is no one perfect mixture. The success of each nutrient formula depends on the conditions it is used in and what plants are being grown.
Many hydroponic gardeners use a pre-mixed nutrient formula that they simply add water to. These formulas contain all the minerals and nutrients that a plant needs, in the correct proportions and are available in powder or liquid form.
The macro nutrients a plant needs include:
The trace elements (used in minute quantities) a plant needs include:
NUTRIENT REQUIREMENTS AND TESTING
Many hydroponic formulas have been developed over the past 40 years with some designed for specific plants while others are designed for general hydroponic gardening. For plant growth, the concentration of individual elements must stay within certain ranges that have been determined through scientific experimentation.
The average concentration of these elements should fall within these parameters:
*PPM = parts per million
Nitrogen (nitrate form) 70 -300 PPM
Nitrogen (ammonium form) 0 -31 PPM
Potassium 200 -400 PPM
Phosphorous 30 -90 PPM
Calcium 150 -400 PPM
Sulfur 60 -330 PPM
Magnesium 25 -75 PPM
Iron .5 -5.0 PPM
Boron .1 -1.0 PPM
Manganese .1 -1.0 PPM
Zinc .02 -.2 PPM
Molybdenum .01 -.1 PPM
Copper .02 -.2 PPM
Plant Usage of Individual Elements
Careful experiments using hydroponics have shown that each of the elements a plant needs has a very specific function in plant growth.
Nitrogen: Nitrogen is a component of proteins, which form an essential part of protoplasm and also occur as stored foods in plant cells. Nitrogen is also a part of other organic compounds in plants such as chlorophyll, amino acids, alkaloids and some plant hormones.
DEFICIENCY: Older leaves turn chlorotic and may eventually die. Plant is stunted Foliage is light green.
EXCESS: Plant becomes over vigorous, leaves become very dark green.
Fruit clusters have excessive growth and fruit ripening is delayed.
Sulfur: Sulfur forms a part of the protein molecule. Plant proteins may have from .5- 1.5% of this element. The sulfhydryl group is a very important group essential for the action of certain enzymes and coenzymes. In additional sulfur is a constituent of ferredoxin and of some lipids.
DEFICIENCY: Younger leaves become yellow with purpling at base. Older leaves turn light green.
EXCESS: Small leaves.
Phosphorous:This element is also a component of some plant proteins, phospholipids, sugar phosphates, nucleic acids, A TP and NADP. The highest percentages of phosphorous occur in the parts of the plant that are growing rapidly.
DEFICIENCY: Uncommon to show toxicity. Secondary manganese deficiency may occur.
EXCESS: No direct toxicity. Copper and zinc availability may be reduced.
Potassium: Potassium accumulates in tissues that are growing rapidly. It will migrate from older tissues to merestematic regions. For example, during the maturing of the crop there is movement of potassium from leaves into the fruit.
DEFICIENCY: Older leaves appear chlorotic between veins, but veins remain green. Leaf edges may burn or roll.
EXCESS: Uncommon to show toxicity. Secondary manganese deficiency may occur.
It is a vital component of epidermal cell walls. It strengthens plants so they can fight off diseases and resist insects, drought, heat and stress. Potassium silicate strengthens plants' ability to transport nutrients and other substances in roots and internal plant cells. Potassium silicate increases cell wall stability, speeds up root cell replication, builds stronger and more extensive root systems, increases nutrient absorption and resistance to stress/drought, and enhances plants' ability to resist pathogens and insects. Silica is a buffering and balancing substance that helps plants deal with potentially-toxic levels of salts, minerals and pollutants. Potassium silicate will give the plants a larger, stronger, more vigorous living infrastructure.
Calcium: All ordinary green plants require calcium. It is one of the constituents of the middle lamella of the cell wall, where it occurs in the form of calcium pectate. Calcium affects the permeability of cytoplasmic membranes and the hydration of colloids. Calcium may be found in combination with organic acids in the plant.
DEFICIENCY: Plant is stunted. Young leaves turn yellow. Blossoms die and fall off. Tomatoes may develop brown spots on the fruit.
EXCESS: No direct toxicity.
Chlorine: It is needed for photosynthesis, It is an enzyme activator that assists production of oxygen from water and in water transport regulation. It is used as the chloride ion. It is a charge balancing ion and for turgidity regulation, keeping plant cells free of infection by disease. It helps open and close stomata by increasing osmotic pressure in cells.
EXCESS: Burnt tips and margins on young leaves. Cuttings will not root well, and seeds may not germinate. Causes leaves to take on a yellowish bronze color and are slow to develop.
Cobalt: Cobalt is a chelation bridge that assists uptake of other metals and nitrogen fixation. It assists enzymes related to the manufacture of aromatic compounds.
DEFICIENCY: Chlorosis of younger leaves.
Magnesium: Magnesium is a constituent of chlorophyll. It occupies a central position in the molecule. Chlorophylls are the only major compounds of plants that contain magnesium as a stable component. Many enzyme reactions, particularly those involving a transfer of phosphate, are activated by magnesium ions.
DEFICIENCY: Older leaves curl and yellow areas appear between veins. Young leaves curl and become brittle.
EXCESS: No direct toxicity.
Iron: A number of essential compounds in plants contain iron in a form that is bound firmly into the molecule. Iron plays a role in being the site on some electron carriers where electrons are absorbed and then given off during electron transport. The iron atom is alternately reduced and then oxidized. Iron plays a very important role in energy conversion reactions of both photo synthesis and transpiration.
DEFICIENCY: New growth pales, veins stay green. Blossoms drop off. Yellowing occurs between veins.
EXCESS: Very uncommon.
Boron: Although the exact function of boron in plant metabolism is unclear, boron does play a regular role in carbohydrate breakdown. Symptoms of boron deficiency include stunted roots and shoot elongation, lack of flowering, darkening of tissues and growth abnormalities.
DEFICIENCY: Young leaves turn yellow. They resemble calcium deficiencies: Symptoms include stunting, discoloration, death of growing tips, and floral abortion. Boron deficiencies stunt roots, mutate leaves, and create brittle leaves that appear bronzed or scorched.
EXCESS: Can cause same type of problems as excess calcium and can resemble symptoms of deficient boron.
Zinc: Zinc is essential to the normal development of a variety of plants. Large quantities of zinc are toxic to plants.
DEFICIENCY: Leaves become chlorotic between veins and often develop necrotic spots.
EXCESS: Reduces availability of iron.
Manganese: The importance of manganese as an activator of several enzymes of aerobic respiration explains some of the disruptive effects of a manganese deficiency on metabolism. The most obvious sign of a manganese deficiency is chlorosis. Manganese chlorosis results in the leaf taking on a mottled appearance.
Copper: Copper is a constituent of certain enzyme systems, such as ascorbic acid oxidize and cyto chrome oxidize. In addition "copper is found in plastocyanin, part of the electron-transport chain in photosynthesis".
DEFICIENCY: Pale yellow. Leaves become spotted. Plant is stunted.
EXCESS: May reduce availability of iron.
Molybdenum: Molybdenum is important in enzyme systems involved in nitrogen fixation and nitrate reduction. Plants suffering molybdenum deficiency can absorb nitrate ions but are unable to use this form of nitrogen.
DEFICIENCY: Older leaves turn yellow and leaf margins curl.
EXCESS: Rare. Tomato leaves may turn bright yellow.
MIXING AND TESTING SOLUTIONS
Deficiencies and Excesses: Since there is no soil to act as a buffer, your hydroponic crops will quickly respond to a nutrient deficiency or toxicity. Nutrient deficiencies are more common than excesses, with the most common deficiencies being nitrogen, iron and magnesium.
Deficiencies and excesses can be avoided by following a routine mixing procedure and schedule, daily monitoring of your nutrient solution and adequate feeding of the plants. If you have an extreme deficiency or toxicity, the plants will respond quickly and symptoms such as discoloration of foliage will occur. A minor deficiency or toxicity may not initially show symptoms but eventually will affect plant growth, vigor and/or fruiting.
Measuring Conductivity: Conductivity is a measure of the rate at which a small electric current flows through a solution. When the concentration of nutrients is greater, the?current will flow faster. When the concentration of the nutrients is lower, the current will flow slower.
You can measure your nutrient solution to determine how strong or weak it is with an EC (electrical conductivity) or TDS (total dissolved solids) meter. An EC meter usually shows the reading in either micromhs per centimeter ?(uMho/cm) or microsiemens per centimeter (uS/cm). 1.0 uMho/cm is?equivalent to 1.0 uS/cm. A TDS meter usually shows the reading in milligrams per liter(mg/l) or parts per million (ppm). EC is generally measured at 77 F (25 C). If the temperature of the solution is raised, the EC will read higher, even though no nutrients have been added. If the temperature drops below 77 F (25 C), the EC will decrease.?Therefore, it is important to always measure your EC at a consistent temperature of 77 F (25 C). Some EC and TDS meters compensate for varying temperatures.
Another measurement in conductivity is CF (conductivity factor) which is expressed on a scale of I -100. Pure water containing no nutrients is rated at 0 and maximum strength nutrients would rate 100.
Some general guidelines for EC levels are as follows:
(such as tomatoes, cucumbers)
(such as lettuce, basil)
||1600 -1800 mMho/cm
1120 -1260 ppm
|1400 -1600 mMho/cm
980 -1120 ppm
1680 -1820 ppm
|Low light conditions
||2800 -3000 mMho/cm
| 2000 mMho/cm (winter)
|High light conditions
||2200 -2400 mMho/cm
|1600 mMho/cm (summer)
Hydroponic Nutrient Mixes
A gardener can purchase all of these minerals separately and mix their own hydroponic fertilizer. Unfortunately, the fertilizers that make up a hydroponic formula aren't sold as pure nitrogen or pure potassium, so it gets more complex. They are sold as chemical compounds, such as calcium nitrate, potassium nitrate, magnesium sulfate, potassium sulfate and mono potassium phosphate.
Since there are many dependable pre-mix hydroponic formulas available, it is generally more efficient and more economical to use a proven formula that contains all of the above mentioned nutrients in the correct quantities for plant growth. one that you simply add to water.
Whether you are using a pre-mixed formula or "creating your own" it is important to follow these guidelines:
1. Weigh or measure the nutrients carefully.
2. Place the nutrients in separate piles or containers to be sure the proportions make sense.
3. Be sure no components are left out or measured twice.
4. Accuracy should be within 5%.
5. When you are sure the proportions are correct, pour your nutrients into the water in the mixing containers and stir vigorously. Nutrients will dissolve best in warm water.
6. Measure the nutrient concentration level and record it.