Nutrients

There are sixteen elements which are generally considered to be essential for good plant growth with adequate light, climate and environment conditions.

The macro elements are those required in "high" concentrations: Carbon (C), Hydrogen (H), Oxygen (O), Nitrogen (N), Phosphorus (P), Potassium (K), Calcium (Ca), Sulfur (S), and Magnesium (Mg). Carbon must be supplied to the plant as carbon dioxide gas (CO2). Hydrogen is available in sufficient quantities from the atmosphere and Oxygen is supplied from well-aerated nutrient solutions or directly to the roots.

The micro elements are also essential for growth, but required in smaller concentrations. Generally the micro elements are thought to be: Iron (Fe), Chlorine (Cl), Manganese (Mn), Boron (B), Zinc (Zn), Copper (Cu), and Molybdenum (Mo). Certain plant species may need others for good growth: Silica (Si), Aluminum (Al), Cobalt (Co), Vanadium (V), and Selenium (Se).

Carbon must be supplied to the plant as carbon dioxide gas (CO2) In the atmosphere, CO2 content is fairly constant, about 390 ppm which is sufficient to promote good growth. Carbon dioxide (CO2) is necessary for plants to enable photosynthesis. Without CO2, or without enough, plants will not be able to thrive. Many hydroponic growers find it helps plant growth to provide an extra amount of CO2. This can be done in a variety of different ways. Growers using CO2 enrichment have claimed to see a 20 to 30% increases in yields. The two most common ways to increase the amount of CO2 in your hydroponic system is by utilizing bottled CO2 or by purchasing a CO2 generator.

During high temperature CO2 enrichment would not be practical either as you will need to keep constant ventilation and continual air movement through the crops so that moist air is removed and humidity levels kept down below 80 percent (to prevent many fungal diseases). CO2 would be rapidly lost to the outside. CO2 will be constantly replaced if the ventilation system is working well, so the plants will not suffer from CO2 depletion.

The most popular method of introducing added CO2 is the bottled CO2 method. This involves a system that includes a CO2 tank, a flow meter, a pressure gauge and a valve. The tank itself holds the CO2 gas. This gas is released through the valve, which must have some type of timer attached to it to help regulate the use of the CO2. Both the flow meter and pressure gauges help the grower judge whether the level of CO2 is appropriate for his or her needs. It is important to note here that, while increasing CO2 levels can help plants grow, allowing too much CO2 into the growing environment will have the opposite effect and your plants will perish. Growers need to research in advance to see what level of CO2 is recommended for the crop being grown.

Using a CO2 generator is more cost effective and somewhat easier. However, this method also has the added element of increased heat that will need to be taken into account and compensated for by including an air-cooling system of some type in your growing environment. CO2 generators work to produce CO2 by burning either propane or natural gas. Most systems are placed on a timer that releases the burned fuel at a regulated time. The biggest hazard possible with a CO2 generator is that it is essential you keep it in perfect working order. Defective units will produce carbon monoxide instead of CO2 if they are not working properly. This will not only kill your plants, but may very well kill any humans who enter the growing environment.

One more expensive way of producing additional carbon dioxide in the system is by the use of dry ice. Dry ice is actually a solid form of CO2. When allowed to "melt" it returns to its gaseous state. This method should really only be used in a pinch. There is almost no control over the amount of gas released into the air or at what rate the dry ice will become gas. There is a lot of room for potential danger to plants using this method.

Adding extra CO2 will not, however, help increase plant growth unless light and temperature are also at optimum levels. Plants enjoying elevated levels of CO2 can be expected to increase fertilizer and water requirements. Proper nutrition and water are essential factors in optimal growth. All these factors must be strong and be working together for best results.

Flue gases from a hot water boiler burning natural gas as a source of CO2, It is important that the CO2 be free of contaminate gases, as plants are extremely sensitive to many gases, especially ethylene.

C02 Application:

Rooted Cutting Stage

Adding C02 to plants at the rooted cutting stage - for about two weeks - produced two benefits: faster early growth and greater final crop yield, even without extra C02 during green growth or crop production! This is useful information for the grower since a little extra carbon dioxide for rooted cuttings can help plants so much. If you use tall, clear covers over your baby plants, release a little C02 under the cover to raise the C02 levels to about 600 PPM. Remove covers to let in fresh air after a few hours, and be sure plants have only fresh air (no extra C02) during dark periods. The two-week period leading up to transplanting is the most effective time for this C02 technique. This does not work for seedlings

Transplant Stage

Adding carbon dioxide during transplanting stage is not recommended, since plants are adjusting to new growing conditions and can make do with regular C02 levels in the air.

Vegetative (Green Growth) Stage

Once plants are 'established' in green growth stage (full light levels, full strength fertilizers, spreading roots and new top growth), it's time to consider adding C02 to your rapidly-growing plants. Plants with a long green-growth period (21 days and more) would benefit from C02 enrichment, growing to the desired size more quickly.

Long Day Crops

Some crops, called 'long day plants', produce their crops during summer, while continuing to put out new leaves and stems. Tomatoes and roses are typical long-day crops which benefit from supplemental C02 right through green growth/crop production stages. These plants do not go through a separate transition stage like short-day crops, so additional C02 can be applied (during the light cycle) through the life of the plants.

Short-Day Crops

'Short-day' crops have a definite 'transition' stage before flower or crop production begins, affecting C02 applications. (Short-day plants produce green growth during spring and summer, and flowers and crop in autumn, responding to the longer nights by beginning crop production. Chrysanthemum and hardy hibiscus are examples of this category of plant). Since C02 is most useful when established plants are actively growing, shut off your tank until crops pass through this transition stage and save the extra C02 for use when crops begin producing flowers. Holding off on extra carbon dioxide while plants go through the transition from green growth to crop production should help keep plants bushy and compact while they decide what they're supposed to do next and reduce 'stretching' problems so common to the early transition period. In fact, if your short-day crop has a history of stretching, cut off the extra C02 two weeks before the end of green growth stage.

Flower And Crop Production Short-Day Plants

Once crops are 'established' into crop production stage (full light levels, full strength food, plants actively producing crop) resume C02 enrichment - if all goes well you could consider increasing the nutrient strength gradually for periods of maximum growth during this stage. As growth slows and crop is finishing up, cut back on C02.

Fine-Tuning

After 7-14 days, your crops will tell you: how many plants are gaining from the extra C02.How much it is helping your plants. You can reposition oscillating fans or add more oscillating fans, add C02 airlines or increase C02 flow rate if growth rate is uneven or some plants need more C02. Usually growers become very enthusiastic about adding C02 at this point, since they can see how it's helping. If little or no effect on growth is seen, check growing conditions for limiting factors, high temperatures, poor air movement, excess humidity levels, bugs, disease or incorrect nutrient mix all interfere with C02 uptake and growth.

Hydrogen is available in sufficient quantities from the atmosphere.

Oxygen Plants can derive oxygen from air or water. In nature, plant roots receive water saturated with oxygen following a rainfall. As the soil begins to dry, air permeates so the roots can breathe and absorb oxygen. During watering, the roots receive both moisture and dissolved minerals.

In the atmosphere, oxygen content is fairly constant, about 18 percent. But in water the oxygen content can vary greatly. This is because oxygen dissolves into water at different rates depending upon variables like temperature and pressure. Putting it simply, the colder the water, the more dissolved oxygen it can hold and conversely, the warmer the water, the less oxygen it can hold.

Oxygen Life began in the oceans, first in simple forms, algae for example, and later evolving into more complex forms. Common to practically all forms of life on Earth today, is the need for oxygen.

In aquatic environments-oceans, lakes, rivers, etc., most life must draw their oxygen out of tile water, which contains dissolved oxygen. For example, fish take water in through their gills to extract oxygen. Terrestrial animals have lungs that can draw oxygen in with air. In both cases, the oxygen is essential for life, though the mechanism for deriving oxygen is quite different: gills versus lungs.

In the atmosphere, oxygen content is fairly constant, about 18 percent. But in water the oxygen content can vary greatly. This is because oxygen dissolves into water at different rates depending upon variables like temperature and pressure. Put simply, the colder the water, the more dissolved oxygen it can hold and conversely, the warmer the water, the less oxygen it can hold.

The value of high oxygen levels in life-containing water is well demonstrated by comparing the richness of life in Arctic waters to that found in tropical waters. In Arctic waters, huge populations of plankton provide fish, sea mammals and a myriad of other life forms with food. This is possible because of the very high levels of dissolved oxygen in the cold Arctic waters.

Warm tropical waters cannot hold high levels of dissolved oxygen, so only those life forms, which have adapted to lower levels of dissolved oxygen can thrive. Tropical oceans are sometimes described as "underwater deserts" because of the limited life forms they support.

The effect temperature and pressure have on the solubility of gases is best described with the carbonated drink example. When you open a bottle of soda or beer, bubbles of carbon dioxide (CO2) begin to form and rise as the compound is released from the bottle. This is the result of a drop in pressure that occurs when the bottle is opened. If the liquid is very cold, the gas release will be slow, but if it is warm and shaken before opening, the CO2, will surge from the open bottle.

Oxygen behaves very much in the manner as CO2 does with regard to solubility in water-according to temperature and pressure. Water at a temperature of 65°F (18°C) has an oxygen capacity twice that of water at 85°F (29°C).

It is important to also understand that temperature and pressure are not the only factors that can limit dissolved oxygen content in water. As organisms draw oxygen from water, it must be replaced as quickly as they extract it. In aquariums, it is common practice to bubble air through the water to charge it with oxygen. This is not an especially powerful way to add oxygen to water, but it works with fish tanks that hold only a small amount of fish in many liters of water. A far more effective way to charge water with oxygen is to spray the water through the air, which many hydroponic growers do to supply their rapidly growing plants with the large amount of oxygen they need to remain healthy.

Plants can derive oxygen from air or water. In nature, plant roots receive water saturated with oxygen following a rainfall. As the soil begins to dry, air permeates so the roots can breathe and absorb oxygen. During watering, the roots receive both moisture and dissolved minerals. If plants are over-watered, their roots sit in soggy, saturated soil and they can die of oxygen deficiency. Over watering is one of the most common causes of plant death.

Some plants have adapted to be able to survive in deficient or stagnant water such as water lilies, rice and some carnivorous plants. Most other plants have a much lower tolerance for oxygen deficiency and cannot sit in over-saturated water for very long.

Oxygen In Hydroponics

If a plant's roots are suspended in water, it will absorb oxygen rapidly. If the oxygen content of the water is inadequate, the plant growth will slow in proportion to oxygen availability. Thus the trick is to co-ordinate the supply of water, nutrient and oxygen with the crops' needs according to other environmental factors like temperature of air and water, CO2 levels, ventilation, humidity, moisture capacity of the rooting media, size and type of crop, and day length. This can be difficult in some extreme conditions, but when applied properly the results can be quite dramatic. Hydroponic growers stimulate plant growth by controlling the amount of water, minerals and oxygen in the nutrient solution. These growers work within a narrow realm between irrigating their crop and allowing oxygen into the root zone. Ebb and flow hydroponic systems are based upon the natural principle of irrigation and oxygenation of plant roots. Mineral-rich water is pumped into a grow medium in which the crop is planted. The irrigation ceases and the water quickly drains away. Oxygen follows and fills the grow medium, allowing the roots to breathe. The roots release CO2, and absorb oxygen. Then the irrigation is repeated and drained away again, basically emulating nature but very quickly. This basic hydroponic method is very reliable; it has been used for decades with different mediums such as gravel, sand, wood chips, sawdust, perlite and Rock Wool.

The down side of ebb and flow hydroponics is that the crop is provided with moisture and mineral nutrients at alternating times from oxygen. In other words, when the roots are breathing, they are not being provided with a constant stream of moisture and nutrients. If the media is too absorbent, then the irrigation cycles must be infrequent to allow time for oxygen to penetrate the roots.

"Constant drip" is a more recent irrigation method designed to level out the availability of moisture, minerals and oxygen. Mineral-rich water is constantly provided in a slow drip to plants that grow in a rapidly draining media. The idea is to maintain a constant balance of moisture and minerals without drowning the crop. It can be somewhat tricky to consistently provide a perfect balance. On a hot summer's day, a large plant can transpire a lot of moisture, so water must be provided at a far higher rate than would be required on a cooler day for a small plant.

In recent decades, the leaders in the development of hydroponic technology have moved into "water-culture" methods and away from rooting media. The first and certainly one of the best recognized is the Nutrient Film Technique (N.F.T.), developed in England in the sixties and seventies and made famous by Dr. Alan Cooper. A breakthrough in its day, N.F.T. was based upon the principle of a very thin film of nutrient-rich water flowing slowly over plant roots held within a plastic envelope. The idea is that the nutrient film provides both moisture and nutrients while above it the roots receive a constant supply of oxygen. Today N.F.T. is widely used and well respected by commercial growers and scientific researchers throughout the world. The only drawback is that there is a fairly critical balance between the right amount of moisture and air required in the rooting envelope. If the film is too deep, then the plants will suffer from oxygen deficiency that can lead to root disease. On the other hand, if the pump fails and the film of moisture is interrupted, even for a relatively brief time, the crop can be lost. Because of this drawback, a more reliable and less risky method of water-culture was sought, so "Aeroponics" arose. Aeroponic systems provide roots with a spray of nutrient rich water. Generally, the plant is supported with its roots dangling in the air. A fine mist of nutrient solution is constantly or intermittently sprayed over the roots. This is a great method as long as there is no failure in the pumping system or clogging of spray nozzles...still not completely forgiving or reliable and generally expensive and tricky to set up and run.

The next generation of water cultivation methods was "aero-hydroponics," in which the root zone is divided into two sections. The root tips are immersed in a constantly flowing stream of nutrient solution while the upper roots hang in an air gap and are sprayed or misted with nutrient solution to provide optimum oxygen levels. This is a superb method since a pump failure does not result in water loss to the roots. Generally, aero-hydroponics is more forgiving than the other water-culture methods. Rather than causing dehydration of the crop, pump failure will result in oxygen deficiency from which most crops can recover without a disaster, provided the pump is fixed quickly.

The common link in all of these methods of hydroponic plant cultivation can be found in the oxygen content of the water. As you now understand, warm nutrient is somewhat oxygen deficient, which can have a lot of meaning for a hydroponic grower. Many root diseases, including fungus infestations can proliferate in oxygen deficient environments. I first realized the magnitude of this phenomenon when I observed Pythium destroying crops growing in Rock Wool. In this case the oxygen deficiency started when the Rock Wool was over-watered. The plants were growing in a saturated sponge. As the Rock Wool dried out, the situation improved, but the next watering led to saturation again. The problem was compounded by the presence of fungus gnats, which seemed to be the vector, or source, of the Pythium. One thing led to another until ultimately, the crop was lost. From this model i learned the importance of deeply analysing problems to learn from experience. Gnat larvae ate and damaged the plants' roots; oxygen deficient conditions caused by high temperature and over-watering stimulated Pythium and the Pythium entered the impaired roots to destroy the crop. In nature, many variables can interact, causing wonderful-or horrible- things to happen. When the plants grow well, there is a lot more things going on than you realize. Similarly, when things go wrong you must look deeper than the obvious to find answers. By better understanding the physical chemistry of water, you can obtain a deeper and richer comprehension of the many phenomena to observe while growing plants.

Dissolved Oxygen

Most of the existing hydroponic production systems for production grow plants on substrates such as rockwool, coco coir and sawdust etc. The root zone oxygen level can be alarmingly low when using these conventional systems due to the low air porosity of some of the growth substrates, especially at the later stage when the substrates are compacted, and in combination with some improper irrigation practices.

In addition, most of the current hydroponic production systems are irrigated with nutrient solution delivered through black tubing and drippers to the plants. During the early stages of crop development, when the canopy is not closed, these irrigation tubes are directly exposed to heat. The irrigation solution temperature can rapidly reach a high level which can cause the solution to hold less oxygen.

The combination of the aforementioned factors can cause serious oxygen deficiency which in turn can make plants susceptible to root diseases, such as Pythium spp. In fact, it is reported by some growers that crops were lost at the early stage (before canopy was closed) due to Pythium spp. which was probably induced by low root zone oxygen. A well oxygenated root zone is essential for a healthy root system (nutrient uptake and root growth/maintenance), and the prevention of root borne diseases. Oxygen deficiency in the root zone can lead to poor root and plant performance and an increase in the incidence of disease.

During high temperatures the plant uses more water and needs more oxygen this oxygen is supplied by the roots. If there is not enough oxygen the plant will shut down and stop transpiering.

If water is stored in reservoirs they need to be aerated as this will keep the water circulating and a higher level of oxygen in the water. Oxygen is depleted in a reservoir by heat and by alga growing in the reservoir

Nitrogen is a chemical element with symbol N and atomic number 7 Elemental nitrogen in the atmosphere cannot be used directly by either plants or animals, and must be converted to a reduced (or 'fixed') state to be useful for plants. Plants are able to assimilate nitrogen directly in the form of nitrates that may be present . Or the result from nitrogen fixation by lightning and other atmospheric electric phenomena. Specific bacteria (e.g., Rhizobium trifolium) possess nitrogenase enzymes that can fix atmospheric nitrogen into a form (ammonium ion) that is chemically useful .As a component in fertilizer Calcium nitrate, also called Norgessalpeter (Norwegian saltpeter) is used. It is produced by treating limestone with nitric acid, followed by neutralization with ammonia. Nitrogen is important for the proper development of chlorophyll (the green in leaves) used in photosynthesis. Overdosing of nitrogen can cause accelerated growth at the expense of structural strength. Too much available nitrogen can also inhibit flowering

Phosphorus is a chemical element with symbol P and atomic number 15. The majority of phosphorus-containing compounds are produced for use as fertilizers. For this purpose, phosphate-containing minerals are converted to phosphoric acid. Two distinct routes are employed, the main one being treatment of phosphate minerals with sulfuric acid. The other process utilizes white phosphorus, which may be produced by reaction and distillation from very low grade phosphate sources. The white phosphorus is then oxidized to phosphoric acid and subsequently neutralized with base to give phosphate salts. Phosphorus is not found free in nature, but it is widely distributed in many minerals, mainly phosphates. Inorganic phosphate rock, which is partially made of apatite (an impure tri-calcium phosphate mineral), is today the chief commercial source of this element. Phosphorus is required for photosynthesis, blooming, and root development. Overdosing of phosphorus may cause iron and zinc deficiencies.

Potassium is a chemical element with symbol K and atomic number 19. Agricultural fertilizers consume 95% of global potassium chemical production, and about 90% of this potassium is supplied as KCl. The potassium content of most plants range from 0.5% to 2% of the harvested weight of crops, conventionally expressed as amount of K

Modern high-yield agriculture depends upon fertilizers to replace the potassium lost at harvest. Most agricultural fertilizers contain potassium chloride, while potassium sulfate is used for chloride-sensitive crops or crops needing higher sulfur content. The sulfate is produced mostly by decomposition of the complex minerals kainite(MgSO4·KCl·3H2O) and langbeinite (MgSO4·K2SO4). Only a very few fertilizers contain potassium nitrate. Potassium is important for photosynthesis, carbohydrate and protein creation, and disease resistance. Overdosing potassium can result in calcium- and magnesium deficiencies.

Calcium is a chemical element with symbol Ca and atomic number 20. Calcium is not naturally found in its elemental state. Calcium occurs most commonly in sedimentary rocks in the minerals calcite, dolomite and gypsum. It also occurs in igneous and metamorphic rocks chiefly in the silicate minerals: plagioclases, amphiboles, pyroxenes and garnets. Calcium is reactive and soft for a metal; though harder than lead, it can be cut with a knife with difficulty. It is a silvery metallic element that must be extracted by electrolysis from a fused salt like calcium chloride. Used in making cell walls, and in some enzyme reactions, calcium provides a base for the neutralization of organic acids. It facilitates the activities of growing points (meristems), especially with root tips. It may be of importance in nitrogen absorption.

Sulfur or sulphur is a chemical element with symbol S and atomic number 16. Sulfur occurs naturally as the pure element (native sulfur) and as sulfide and sulfate minerals. It is an abundant, multivalent non-metal under normal conditions. Elemental sulfur is a bright yellow crystalline solid when at room temperature. Used in amino acid and enzyme production. Cannabis can generally tolerate quite high concentrations of sulfur, and overdosing is uncommon.

Magnesium is a chemical element with symbol Mg and atomic number 12. Magnesium only occurs naturally in combination with other elements, where it invariably has a +2 oxidation state. Magnesium is found in over 60 minerals, dolomite, magnesite, brucite, carnallite, talc, and olivine are of commercial importance. Plants require magnesium to synthesize chlorophyll.

Iron is a chemical element with symbol Fe and atomic number 26. Iron chelate, also known as chelated iron, is a soluble complex of iron, sodium and a chelating agent such as (EDTA) or (EDDHA), or others, used to make the iron soluble in water and, for the purposes of agriculture, accessible to plants. Iron is a necessary trace element found in nearly all living organisms. Iron participates in many biological oxidations . Magnesium is a key element in making chlorophyll and used in certain enzyme reactions. Magnesium also assists in phosphorous uptake and carbon fixation.

Chlorine is a chemical element with symbol Cl and atomic number 17. The most common compound of chlorine, sodium chloride (common salt)

Chloride is a component of the salt that is deposited in the earth or dissolved in the oceans — about 1.9% of the mass of seawater is chloride ions.

Manganese is a chemical element with symbol Mn and atomic number 25. It is not found as a free element in nature; it is often found in combination with iron, and in many minerals. The most important manganese ore is pyrolusite (MnO2)

Manganese is also important in photosynthetic oxygen evolution in chloroplasts in plants.

Boron is a chemical element with symbol B and atomic number 5. Boron is concentrated on Earth by the water-solubility of its more common naturally occurring compounds, the borate minerals. These are mined industrially as evaporites, such as borax and kernite. Boron is essential to life. Small amounts of boron compounds play a strengthening role in the cell walls of all plants, making boron necessary.

Zinc, is a chemical element with symbol Zn and atomic number 30. The most common zinc ore is sphalerite (zinc blende), a zinc sulfide mineral.

Zinc deficiency is the most common of micronutrient deficiency in plants. Excess zinc is toxic to plants.

Copper is a chemical element with symbol Cu (from Latin: cuprum) and atomic number 29. Copper is present in the Earth's crust at a concentration of about 50 parts per million (ppm), where it occurs as native copper or in minerals such as the copper sulfides chalcopyrite and chalcocite. Copper proteins have diverse roles in biological electron transport and oxygen transportation.

Molybdenum is a chemical element with symbol Mo and atomic number 42. Molybdenum does not occur naturally as a free metal on Earth, but rather in various oxidation states in minerals. Molybdenum is found in such minerals as wulfenite (PbMoO4) and powellite (CaMoO4), the main commercial source of molybdenum is molybdenite (MoS2). Molybdenum is mined as a principal ore, and is also recovered as a byproduct of copper and tungsten mining.

Silicon: Potassium Silica is an easy to use liquid that provides supplemental potassium (3.7%) and silicon (7.8%). The latest research proves that plants benefit in many important ways from supplemental soluble silicon. These benefits include greater tolerance of environmental stresses, such as cold, heat, drought, salinity, mineral toxicity or deficiency, improved growth rates and resistance to insects and fungi. Soluble silicon promotes natural fungal defense mechanisms in plants, significantly reducing and, in many cases eliminating entirely, the need to use fungicides. Silicon deposited in epidermal cell walls makes plants resistant to small sucking insects. The resulting increased mechanical strength in epidermal cell walls enhances leaf presentation and stem strength. Soluble silicon enhances metabolic functions and improves pollen fertility, fruit and flower count.

Silicon Increases Resistance to Pathogens

Silicon deposition in the epidermal cells of plants act as a barrier against penetration of invading fungi such as powdery mildew and Pythium. Following a fungal infection, greater deposits of silicon are found around the affected plant tissue showing that silicon is selectively accumulated at the site. Silicon is also deposited in the cell walls of roots where it acts as a barrier against invasion of the stele by parasites and pathogens. Tests conducted on cucumbers, melons and tomatoes determined that soluble silicon must be available to the plant during the period of infection by fungal spores. The silicon is deposited at the sites of infection to form stronger, harder cell walls to deter the fungus. Silicon also stimulates the production of polyphenolic compounds which form part of a plant's natural defenses against fungal infection and insect attack. Silicon is rapidly bound in leaf tissue and will be deposited in a non-translocatable form within 24 hours. Therefore a continuous source of soluble silicon is very important to combat pathogens. This can be from constant feeding in hydroponics or from retention in the growing medium with soils or soilless mixes.

In some plants, foliar applications appear to lead to even lower rates of disease probably because deposits of silicon compounds on the leaf surface promote physical barriers to the infection process. Foliar sprays of soluble silicon have also been shown to be effective for control of aphids and other sucking insects on many plants. Epidermal cell walls containing silicon deposits act as a mechanical barrier to the styles and mandibles of sucking and biting insects In addition to the silicate deposits in the leaves, the intracellular content of silicic acid also acts as an effective sap sucking inhibitor for many insects.

Silicon Increases Metabolic Rates and Stress Resistance

Research shows that silicon benefits plants in the following ways: improved resistance to wilt, resistance to water stress (heat and drought), enhanced leaf presentation resulting in improved light interception, enhanced reproductive growth, and increased tolerance of excessive phosphorus, manganese, sodium and aluminum concentrations, zinc deficiencies and cold temperatures. Silicon, deposited in the cell walls, forms a protective layer reducing transpiration through the outer cells. Silicon deposits in the cell walls of xylem vessels prevent compression of the vessels under conditions of high transpiration caused by drought or heat stress. Temperatures much above 90°F cause plants to virtually cease their metabolic functions because water is lost through transpiration faster than it can be replaced via the plant's root system. This results in harmful increases in intracellular mineral concentrations that inhibit plant functions. Increased levels of silicon in cell walls reduce transpiration loss caused by higher temperatures thus allowing continued metabolic functions at higher temperatures. Plants wilt less, resist sunburn and are generally more tolerant of heat stresses. Cuttings and plugs are more tolerant of the stresses encountered during root formation and potting up as a result of decreased transpiration.

Silicon has also been shown to result in higher concentrations of chlorophyll per unit area of leaf tissue. This means that a plant is able to tolerate both lower and higher light levels by using more of the available light. Moreover, supplemental levels of soluble silicon have been shown to produce higher concentrations of the enzyme RUBP carboxylase in leaf tissue. This enzyme regulates the metabolism of carbon dioxide and enables the plant to make more efficient use of available levels of CO2.

Silicon deficiencies often are indicated by malformation of young leaves and a failure of pollination and fruit formation in many cases. Plants with silicon added to the nutrient formula also show a decrease in leaf and flower senescence. The shelf life of cut flowers, specialty pot crops and plugs is also extended. Leaves are thicker and darker green compared to those grown without soluble silicon.

Water The first thing visitors from another world would see upon their approach to Earth is water. Our blue planet sparkles like a jewel bathed in sunlight. Water is apparent from a great distance in all three natural states: liquid, solid (glaciers) and gas (water vapor in the atmosphere).

Life on Earth is based upon water. Just as the majority of the planet is covered with water, all life on Earth is comprised of water. Thus, a comprehension of life necessitates an understanding of water in its relationship to life.

When we study the three states of water liquid, solid, gas-we are studying the "physical chemistry" of water; that is, the relationship between physics and chemistry in water. These three states are in part defined in terms of temperature, In simple and approximate terms, we can say that water which is colder than 32°F (0° C) is solid, or ice. Water which is above 212°F ( 100°C) is a gas, or steam. Between 32°F and 212°F (0° C and 100°C), water is in liquid form.

However, water can exist below 212°F (100°C) as a vapor. If you exhale onto your eyeglass lenses to clean them, you have exhaled a water vapor at a temperature below 212°F. The water that makes up clouds in the Earth's atmosphere is also well below 212°F, so you see there is quite a "grey area" between the defining temperature extremes which separate water into its three states. A limited amount of water may be in the vapor phase as "humidity." This amount is a function of temperature: If it is cold, less water is present at 100 percent humidity than if it is hot. We measure this water in air as a "partial pressure" of water, which can increase with temperature and reaches sea level atmospheric pressure (14.7 psi) at 212°F, the boiling point of water.

Water Quality

Good, consistent water quality is essential for hydroponics. Fresh water free from pesticide runoff, microbial contamination, algae, or high levels of salts must be available throughout the year. The levels of pH and alkalinity (measured as carbonates and bicarbonates) of the raw water affects the absorption of certain nutrients by the roots. Water pH levels above the desirable range (5.0 to 7.0) may hinder absorption of some plant nutrients; pH levels below this range permit excessive absorption of some nutrients, which may lead to toxic levels of those elements.

In arid areas, or areas near salt water, the concentration of sodium chloride (NaCl) may be too high for optimal plant growth (greater than 50 parts per million or 1.5 mmol/liter). The hardness of the incoming water will also have an effect on the nutrient solution. Hardness is a measure of the concentrations of calcium and magnesium carbonates, which are often quite high in areas of limestone rock. The naturally occurring concentrations of these minerals in hard water must be taken into consideration when calculating the amount of nutrient salts to add to the nutrient solution, and may interfere with the availability of other essential nutrients, such as iron. Similarly, concentrations of other essential elements may be found in very high levels in poor quality water. For example, water may carry high levels of iron, selenium, boron, or sulfur; and municipal water may have undesirably high levels of chlorine.

The electrical conductivity of good quality raw water should be below 0.5 mS/cm or mmhos/cm. It is advisable to invest in a complete analysis of the water quality, including all major and minor elements, microbial contamination and pesticide residues before any further work is done.

Water Treatment

I'm sure you've heard the terms 'hard water' and 'soft water', but do you know what they mean? Is one type of water somehow better than the other? What type of water do you have? Let's take a look at the definitions of these terms and how they relate to water in everyday life.

Hard water is any water containing an appreciable quantity of dissolved minerals. Soft water is treated water in which the only (positively charged ion) is sodium. The minerals in water give it a characteristic taste. Some natural mineral waters are highly sought for their flavor and the health benefits they may confer. Soft water, on the other hand, may taste salty and may not be suitable for drinking.

If soft water tastes bad, then why might you use a water softener? The answer is that extremely hard water may shorten the life of plumbing and lessen the effectiveness of certain cleaning agents. When hard water is heated, the carbonates precipitate out of solution, forming scale in pipes and tea kettles. In addition to narrowing and potentially clogging the pipes, scale prevents efficient heat transfer, so a water heater with scale will have to use a lot of energy to give you hot water. Soap is less effective in hard water because its reacts to form the calcium or magnesium salt of the organic acid of the soap. These salts are insoluble and form grayish soap scum, but no cleansing lather. Detergents, on the other hand, lather in both hard and soft water. Calcium and magnesium salts of the detergent's organic acids form, but these salts are soluble in water.

Hard water can be softened (have its minerals removed) by treating it with lime or by passing it over an ion exchange resin. The ion exchange resins are complex sodium salts. Water flows over the resin surface, dissolving the sodium. The calcium, magnesium, and other cations precipitate onto the resin surface. Sodium goes into the water, but the other cations stay with the resin. Very hard water will end up tasting saltier than water that had fewer dissolved minerals.

Most of the ions have been removed in soft water, but sodium and various anions (negatively charged ions) still remain. Water can be deionized by using a resin that replaces cations with hydrogen and anions with hydroxide. With this type of resin, the cations stick to the resin and the hydrogen and hydroxide that are released combine to form pure water.

Nutrient Solutions

Electrical Conductivity (Ec)

Electrical conductivity is a scientific measurement that relates to the strength of nutrient or mineral salts present in water. It is widely used as an indicator of the level of nutrients used to feed plants in hydroponic gardening.

An electrical current results from the motion of electrically charged particles in response to forces that act on them from an applied electric field. Within most solid materials a current arise from the flow of electrons, which is called electronic conduction. In all conductors, semiconductors, and many insulated materials only electronic conduction exists, and the electrical conductivity is strongly dependant on the number of electrons available to participate to the conduction process. Most metals are extremely good conductors of electricity, because of the large number of free electrons that can be excited in an empty and available energy state.

In water and ionic materials or fluids a net motion of charged ions can occur. This phenomenon produce an electric current and is called ionic conduction.

Electrical conductivity is defined as the ratio between the current density (J) and the electric field intensity (e) and it is the opposite of the resistivity (r, [W*m]):

s = J/e = 1/r

Silver has the highest conductivity of any metals: 63 x 106 S/m.

Water Conductivity

Pure water is not a good conductor of electricity. Ordinary distilled water in equilibrium with carbon dioxide of the air has a conductivity of about 10 x 10-6 W-1*m-1 (20 dS/m). Because the electrical current is transported by the ions in solution, the conductivity increases as the concentration of ions increases.

Thus conductivity increases as water dissolved ionic species.

Electrical Conductivity And TDS

TDS or Total Dissolved Solids is a measure of the total ions in solution. EC is actually a measure of the ionic activity of a solution in term of its capacity to transmit current. In dilute solution, TDS and EC are reasonably comparable. The TDS of a water sample based on the measured EC value can be calculated using the following equation:

TDS (mg/l) = 0.5 x EC (dS/m or mmho/cm) or = 0.5 * 1000 x EC (mS/cm)

The above relationship can also be used to check the acceptability of water chemical analyses. It does not apply to wastewater.

As the solution becomes more concentrated (TDS > 1000 mg/l, EC > 2000 ms/cm), the proximity of the solution ions to each other depresses their activity and consequently their ability to transmit current, although the physical amount of dissolved solids is not affected. At high TDS values, the ratio TDS/EC increases and the relationship tends toward TDS = 0.9 x EC.

In these cases the above-mentioned relationship should not be used and each sample should be characterized separately.

PH

Chart Showing Mineral Uptake In Relation To ph, Hydroponic Solutions Only

Perhaps one of the most overlooked aspects of growing, pH is very important in hydroponic and organic as well as regular "dirt" gardening. pH is measured on a scale of 1-14 with 7 being "neutral". Acids are lower than 7 and alkalis (bases) are above 7.

To be technical, the term pH refers to the potential hydrogen-hydroxyl ion content of a solution. Solutions ionize into positive and negative ions. If the solution has more hydrogen (positive) ions than hydroxyl (negative) ions then it is an acid (1-6.9 on the pH scale). Conversely if the solution has more hydroxyl ions than hydrogen it is alkaline (or base), with a range of 7.1-14 on the pH scale.

Pure water has a balance of hydrogen (H+) and hydroxyl (OH-) ions and is therefore pH neutral (pH 7). When the water is less than pure it can have a pH either higher or lower than 7.

The pH scale is logarithmic, which means that each unit of change equals a ten fold change in the hydrogen/hydroxyl ion concentration. To put it another way, a solution with a pH of 6.0 is 10 times more acidic than a solution with a value of pH 7.0, and a solution with a pH value of 5.0 would be 10 times more acidic than the solution of 6.0 pH and 100 times more acidic than the solution with a 7.0 pH. This means that when you are adjusting the pH of your nutrient solution and you need to move it 2 points (example: 7.5 to 5.5) you would have to use 10 times more adjuster than if you were moving the pH value just 1 point (7.5 to 6.5).

Why Is Ph Important?

When the pH is not at the proper level the plant will lose it's 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 6.0 - 6.5), although most plants can still survive in an environment with a pH of between 5.0 and 7.5.

When pH raises 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 (or die). Some nutrients will precipitate out of solution when the pH drops also.

When you are growing hydroponically checking and adjusting pH is a simple matter, it can be a bit more complicated when growing organically or in dirt. There are several ways to check the pH of the nutrient solution in your hydroponic system.

Paper test strips are probably the most inexpensive way to check the pH of the nutrient solution. These paper strips are impregnated with a pH sensitive dye which changes color when dipped into the nutrient solution. The paper strip is then compared to a color chart to determine the pH level of the solution being checked. These test strips are inexpensive, but sometimes they can be hard to read, because the colors differences can be subtle.

Liquid pH test kits are probably the most popular method to check pH. These liquid test kits work by adding a few drops of a pH sensitive dye to a small amount of the nutrient solution and then comparing the color of the resulting liquid with a color chart. The liquid kits are a bit more expensive than the paper test strips but they work very well, and are normally easier to "read" than the paper indicator strips.

The Most high-tech way to check pH is to use the digital meters. These meters come in a huge array of sizes and prices. The most popular type of pH meter are the digital "pens". These pens are manufactured by several different companies and are very handy and easy to use. You simply dip the electrode into the nutrient solution for a few moments and the pH value is displayed on a LCD display.

The pH meters are very accurate (when properly calibrated) and fast. They need to be cared for properly however, or they will quit working. The glass bulb electrode must be kept clean and wet at all times. The pH meters are actually very sensitive volt meters and are susceptible to problems with the electrode.

The pH meters are slightly temperature sensitive. Many of the pH meters on the market have Automatic Temperature Compensation (ATC), which corrects the reading with respect to temperature. On meters without ATC the pH should be checked at the same time of day each time in order to minimize any temperature related fluctuations.

The pH meters usually need to be calibrated frequently, as the meters can "drift" and to insure accuracy you must check calibration often. The tip needs to be stored in a electrode storage solution or in a buffer solution. The tip should never be allowed to dry out.

Due to the fact that pH meters have a reputation of breaking down without warning it is a good idea to keep an emergency back up for checking pH (paper test strips or a liquid pH test kit), just in case.

Adjusting Ph

There are several chemicals used by the grower to adjust pH. The most popular are probably phosphoric acid (to lower pH), and potassium hydroxide or lime or potash can take it up when it gets too acid (to raise pH). Both of these chemicals are relatively safe, although they can cause burns and should never come in contact with the eyes. Concentrated adjusters can cause large pH changes and can make adjusting the pH very frustrating.

Several other chemicals can be used to adjust the pH of hydroponic nutrient solutions. Nitric acid and sulfuric acid can be used to lower pH but are much more dangerous than phosphoric acid. Food grade citric acid is sometimes used in organic gardening to lower pH.

Always add the nutrients to the water before checking and adjusting the pH of your nutrient solution. The fertilizer will usually lower the pH of the water due to it's chemical make up. After adding nutrient and mixing the solution, check the pH using what ever means you have. If the pH needs to be adjusted add the appropriate adjuster. Use small amounts of pH adjuster until you get familiar with the process. Recheck the pH and repeat the above steps until the pH level is where you want it to be.

The pH of the nutrient solution will have a tendency to go up as the plants use the nutrients. As a result the pH needs to be checked periodically (and adjusted if necessary). To start out I suggest that you check pH on a daily basis. Each system will change pH at a different rate depending on a variety of factors. The type of growing medium used, the environment, kind of plants and even the age of the plants all effect the pH variations.

Fertilizers and acid are normally added into the catchment tank in the form of concentrated stock solutions. The dosing pumps used to inject nutrients and acids into the catchment tank should be chemically resistant at least in those parts that come in contact with the relatively concentrated solutions. Use two pumps for fertilizer and one for acid; their size depends on the size of the operation, but most growers need an average capacity of 10 L/h. The two nutrient pumps used for fertilizer injection should be adjustable so that they can be set to deliver exactly the same volume of liquid. Regulate the operation of the fertilizer and acid injection pumps by their respective controllers. In large installations it may be more economical to replace the dosing pumps with solenoid valves that control the gravity-driven flow of stock solutions.

Nutrients that can accumulate over time include calcium (from hard water), sulfate (from fertilizers), sodium and chloride (from saline water), and possibly others. Under these conditions the background conductivity rises progressively, so proportionate increases in the EC setting of the salinity controller are needed to maintain an adequate nutrient supply.

Unfortunately, no simple and practical procedure exists to determine the changes in background conductivity. Therefore discard the nutrient solution periodically and add new solution into the system. The frequency at which to renew the nutrient solution depends on the stage of crop growth and the conditions, both of which affect the rate of nutrient and water uptake by the crop. Generally, renew the solution every week at the beginning of a crop and twice a month later, when the crop is fully grown or whenever the crop appears to have stopped growing. As the grower gains experience with the system, the solution may need less frequent renewal.

While the NFT operation is being established, weekly chemical analysis of the nutrient solution is essential for crop safety and for familiarizing the grower with the operation; as the grower gains experience, less frequent analysis can be conducted, e.g., twice a month.

Nutrient solution analysis is absolutely necessary in a closed system, where the solution is re-used, and recommended in an open system to verify concentrations of macro and microelements. Plants take up nutrients in varying amounts depending on their needs. Although monitoring pH and EC will give an indication of changes in the nutrient solution, it cannot indicate changes in preferential uptake of particular ions. In a closed system, if no analysis is possible, then the nutrient solution should be completely changed every two weeks.

Plant tissue analysis can provide other information about the growing system. That is, tissue analysis can indicate any problems the plants may be having in absorbing nutrients which are present in the solution. For example, fluctuating pH levels, high cation exchange capacity of the media, high humidity, or diseases and nematodes can prevent nutrient uptake by a plant.

On a commercial scale, nutrient solution and plant tissue analysis is absolutely required. Plant tissue analysis allows the grower to detect a problem in the uptake/assimilation of nutrients which may not be apparent in a nutrient solution analysis. Consult with the testing laboratory for information on sampling and sample prep.

A Basic Formula For Lettuce

Symptoms Of Nutrient Deficiencies And Toxicities

Nutritional disorders can be very complex, involving temperature, humidity, light length and disease as well as nutrient levels. Multiple disorders can produce a syndrome which does not resemble any single disorder. Some growers feel that relying on plant disorder symptoms is a reactive, not a pro-active approach, since by the time symptoms appear, the yields will already have been adversely affected. Symptoms of nutritional disorders should never be ignored, however, and excellent sources of information are available. Professional growers should keep such sources and horticultural experts near at hand, and have their nutrient solutions analyzed routinely.