ALOHA gardeners, I actually planned on doing a post today on N-P-K, what it stands for, and how it effects your plants. I see so many indoor gardeners grow for years without even knowing what N-P-K is and why these chemicals encourage biological responses in plants. One of the most common questions we get here at the blog and in the stores is “can you please help demystify plant food science for me?” I would love to, I have included an extensive amount of links and vocabulary on the subject for all of you loyal PGS Blog readers.. ( Love you guys!)
N-P-K = Nitrogen, Phosphorous, and Potassium
N = Nitrogen 7-9-5
Nitrogen is the first major element responsible for the vegetative growth of plants above ground. With a good supply, plants grow sturdily and mature rapidly, with rich, dark green foliage.
P = Phosphorus 7-9-5
The second major element in plant nutrition, phosphorus is essential for healthy growth, strong roots, fruit and flower development, and greater resistance to disease.
K = Potassium (Potash) 7-9-5 The third major plant nutrient, potassium oxide is essential for the development of strong plants. It helps plants to resist diseases, protects them from the cold and protects during dry weather by preventing excessive water loss.
Fertilizers are chemical compounds applied to promote plant and fruit growth. Fertilizers are usually applied either through the soil (for uptake by plant roots) or by foliar feeding (for uptake through leaves).
Fertilizers can be placed into the categories of organic fertilizers (composed of decayed plant/animal matter), or inorganic fertilizers (composed of simple chemicals and minerals). Organic fertilizers are ‘naturally’ occurring compounds, such as peat, manufactured through natural processes (such as composting), or naturally occurring mineral deposits; inorganic fertilizers are manufactured through chemical processes (such as the Haber process, also using naturally occurring deposits, while chemically altering them (e.g. concentrated triple superphosphate.
Properly applied, organic fertilizers can improve the health and productivity of soil and plants, as they provide different essential nutrients to encourage plant growth. Organic nutrients increase the abundance of soil organisms by providing organic matter and micronutrients for organisms such as fungal mycorrhiza, which aid plants in absorbing nutrients. Chemical fertilizers may have long-term adverse impact on the organisms living in soil and a detrimental long term effect on soil productivity of the soil.
Chemical Content
Fertilizers typically provide, in varying proportions, the three major plant nutrients: nitrogen, phosphorus, potassium known shorthand as N-P-K); the secondary plant nutrients (calcium, sulfur, magnesium) and sometimes trace elements (or micronutrients) with a role in plant or animal nutrition: boron, chlorine, manganese, iron, zinc, copper, molybdenum and (in some countries) selenium.
Organic and Non-organic
Both organic and inorganic fertilizers were called “manure”, derived from the French expression for manual (of or belonging to the hand) tillage, however, this term is currently restricted to organic manure. Though nitrogen is plentiful in the Earth’s atmosphere, relatively few plants engage in nitrogen fixation (conversion of atmospheric nitrogen to a plant-accessible form).
It is believed by some that ‘organic’ agricultural methods are more environmentally friendly and better maintain soil organic matter (SOM) levels. There are some scientific studies that support this position.
History
While manure, cinder and ironmaking slag have been used to improve crops for centuries, the use of fertilizers is arguably one of the great innovations of the Agricultural Revolution of the 19th Century.
Key figures in Europe
In the 1730s, Viscount Charles Townshend (1674–1738) first studied the improving effects of the four crop rotation system that he had observed in use in Flanders. For this he gained the nickname of Turnip Townshend.
Justus von Liebig
Chemist Justus von Liebig (1803–1883) contributed greatly to the advancement in the understanding of plant nutrition. His influential works first denounced the vitalist theory of humus, arguing first the importance of ammonia, and later promoting the importance of inorganic minerals to plant nutrition. Primarily Liebig’s work succeeded in exposition of questions for agricultural science to address over the next 50 years
In England, he attempted to implement his theories commercially through a fertilizer created by treating phosphate of lime in bone meal with sulfuric acid. Although it was much less expensive than the guano that was used at the time, it failed because it was not able to be properly absorbed by crops
Sir John Bennet Lawes
At that time in England, Sir John Bennet Lawes (1814–1900) was experimenting with crops and manures at his farm at Harpenden and was able to produce a practical superphosphate in 1842 from the phosphates in rock and coprolites. Encouraged, he employed Sir Joseph Henry Gilbert, who had studied under Liebig at the University of Giessen, as director of research. To this day, the Rothamsted research station the pair founded still investigates the impact of inorganic and organic fertilizers on crop yields
Jean Baptiste Boussingault
In France, Jean Baptiste Boussingault (1802–1887) pointed out that the amount of nitrogen in various kinds of fertilizers is important.
Metallurgists Percy Gilchrist (1851–1935) and Sidney Gilchrist Thomas (1850–1885) invented the Thomas-Gilchrist converter, which enabled the use of high phosphorus acidic Continental ores for steelmaking. The dolomite lime lining of the converter turned in time into calcium phosphate, which could be used as fertilizer, known as Thomas-phosphate.
Bosch Farben and Haber
In the early decades of the 20th Century, the Nobel prize-winning chemists Carl Bosch of IG Farben and Fritz Haber developed the process that enabled nitrogen to be synthesised cheaply into ammonia, for subsequent oxidation into nitrates and nitrites.
Erling Johnson
In 1927 Erling Johnson developed an industrial method for producing nitrophosphate, also known as the Odda process after his Odda Smelteverk of Norway. The process involved acidifying phosphate rock (from Nauru and Banaba Islands in the southern Pacific Ocean) with nitric acid to produce phosphoric acid and calcium nitrate which, once neutralized, could be used as a nitrogen fertilizer
Industry
British
The Englishmen James Fison, Edward Packard, Thomas Hadfield and the Prentice brothers each founded companies in the early 19th century to create fertilizers from bone meal.
The developing sciences of chemistry and Paleontology, combined with the discovery of coprolites in commercial quantities in East Anglia, led Fisons and Packard to develop sulfuric acid and fertilizer plants at Bramford, and Snape, Suffolk in the 1850s to create superphosphates, which were shipped around the world from the port at Ipswich. By 1871 there were about 80 factories making superphosphateTemplate:Where?.
After World War I these businesses came under competitive pressure from naturally-produced guano, primarily found on the Pacific islands, as their extraction and distribution had become economically attractive.
The interwar period saw innovative competition from Imperial Chemical Industries who developed synthetic ammonium sulfate in 1923, Nitro-chalk in 1927, and a more concentrated and economical fertilizer called CCF based on ammonium phosphate in 1931. Competition was limited as ICI ensured it controlled most of the world’s ammonium sulfate supplies.
North America and other European Countries
Other European and North American fertilizer companies developed their market share, forcing the English pioneer companies to merge, becoming Fisons, Packard, and Prentice Ltd. in 1929. Together they produced 85,000 tons of superphosphate/year in 1934 from their new factory and deep-water docks in Ipswich. By World War II they had acquired about 40 companies, including Hadfields in 1935, and two years later the large Anglo-Continental Guano Works, founded in 1917.
The post-war environment was characterized by much higher production levels as a result of the “Green Revolution” and new types of seed with increased nitrogen-absorbing potential, notably the high-response varieties of maize, wheat, and rice. This has accompanied the development of strong national competition, accusations of cartels and supply monopolies, and ultimately another wave of mergers and acquisitions. The original names no longer exist other than as holding companies or brand names: Fisons and ICI agrochemicals are part of today’s Yara International and AstraZeneca companies.
Major players in this market now include the Russian Uralkali fertilizer company Uralkali (listed on the London Stock Exchange), whose majority owner is Dmitry Rybolovlev, ranked by Forbes as 60th in the list of wealthiest people in 2008.
Inorganic fertilizers (mineral fertilizer)
Naturally occurring inorganic fertilizers include Chilean sodium nitrate, mined rock phosphate, and limestone (to raise pH and a calcium source).
Macronutrients and micronutrients
Fertilizers can be divided into macronutrients and micronutrients based on their concentrations in plant dry matter. There are six macronutrients: nitrogen, phosphorus, and potassium, often termed “primary macronutrients” because their availability is usually managed with NPK fertilizers, and the “secondary macronutrients” — calcium, magnesium, and sulfur — which are required in roughly similar quantities but whose availability is often managed as part of liming and manuring practices rather than fertilizers.
The macronutrients are consumed in larger quantities and normally present as a whole number or tenths of percentages in plant tissues (on a dry matter weight basis). There are many micronutrients, required in concentrations ranging from 5 to 100 parts per million (ppm) by mass. Plant micronutrients include iron (Fe), manganese (Mn), boron (B), copper (Cu), molybdenum (Mo), nickel (Ni), chlorine (Cl), and zinc (Zn).
Tennessee Valley Authority: “Results of Fertilizer” demonstration 1942.
Macronutrient fertilizers
Synthesized materials are also called artificial, and may be described as straight, where the product predominantly contains the three primary ingredients of nitrogen (N), phosphorus (P), and potassium (K), (known as N-P-K fertilizers or compound fertilizers when elements are mixed intentionally).
Reporting of N-P-K
Such fertilizers are named according to the content of these three elements. For example, if nitrogen is the main element, the fertilizer is often described as a nitrogen fertilizer.
Regardless of the name, however, they are labeled according to the relative amounts of each of these three elements, by weight (i.e, mass fraction). The percent of nitrogen is reported directly. However, phosphorus is reported as the mass fraction of phosphorus pentoxide (P2O5), the anhydride of phosphoric acid, and potassium is reported as the mass fraction of potassium oxide (K2O), which is the anhydride of potassium hydroxide.
Fertilizer composition is expressed in this fashion for historical reasons in the way it was analyzed (conversion to ash for P and K mass fractions); this practice dates back to Justus von Liebig.
Mass fraction conversion to elemental values
Since the N-P-K reporting basis just described does not give the actual fraction of the respective elements, some packaging also reports the elemental mass fractions. The UK fertilizer-labelling regulations [10] allow for additionally reporting the elemental mass fractions of phosphorous and potassium, rather than phosphoric acid and potassium hydroxide, but these must be listed in parentheses after the standard values. The regulations specify the factors for converting from the P2O5 and K2O values to the respective P and K elemental values as follows:
In phosphorous pentoxide, the element phosphorous constitutes 43.6% of the total mass of the compound. Thus, the official UK mass fraction (percentage) of elemental phosphorus is 43.6%. [P] = 0.436 x [P2O5]
Likewise, the mass fraction (percentage) of elemental potassium is 83%. [K] = 0.83 x [K2O]
Thus an 18−51−20 fertilizer contains, by weight, 18% elemental nitrogen (N) , 22% elemental phosphorus (P), and 16% elemental potassium (K).
(Note: The remaining 11% [100 - (18 + 51 + 20)] is known as ballast or filler and may or may not be valuable to the plants, depending on what is used as filler.)
Nitrogen fertilizer
Nitrogen fertilizer is often synthesized using the Haber-Bosch process, which produces ammonia. This ammonia is then used to produce other compounds (notably anhydrous ammonium nitrate and urea) which can be applied to fields. These concentrated products may be used as fertilizer or diluted with water to form a concentrated liquid fertilizer, UAN. Ammonia can also be used in the Odda Process in combination with rock phosphate and potassium fertilizer to produce compound fertilizers.
The production of ammonia currently consumes about 5% of global natural gas consumption, which is somewhat under 2% of world energy production.
Natural gas is overwhelmingly used for the production of ammonia, but other energy sources, together with a hydrogen source, can be used for the production of nitrogen compounds suitable for fertilizers. The cost of natural gas makes up about 90% of the cost of producing ammonia. The price increases in natural gas in the past decade, along with other factors such as increasing demand, have contributed to an increase in fertilizer price
Nitrogen-based fertilizers are most commonly used to treat fields used for growing maize, followed by barley, sorghum, rapeseed, soyabean and sunflower[citation needed]. One study has shown that application of nitrogen fertilizer on off-season cover crops can increase the biomass of these crops, while having a beneficial effect on soil nitrogen levels for the cash crop planted during the summer season.
Agricultural versus horticultural fertilizers
In general, agricultural fertilizers contain only 1 or 2 macronutrients. Agricultural fertilizers are intended to be applied infrequently and normally prior to or alongside seeding. Examples of agricultural fertilizers are granular triple superphosphate, potassium chloride, urea, and anhydrous ammonia. The commodity nature of fertilizer, combined with the high cost of shipping, may lead to use of locally available substitutes or materials from the closest and/or cheapest source, which may vary with factors such as the relative cost of transportation by rail, ship, or truck.
In other words, a particular nitrogen source may be very popular in one part of the country while another is very popular in another geographic region only due to factors unrelated to agronomic concerns.
Horticultural or specialty fertilizers, on the other hand, are formulated from many of the same compounds and some others to produce well-balanced fertilizers that also contain micronutrients. Some materials, such as ammonium nitrate, are used minimally in large scale production farming. The 18-51-20 example is a horticultural fertilizer formulated with high phosphorus to promote bloom development in ornamental flowers. Horticultural fertilizers may be water-soluble (instant-release) or relatively insoluble (controlled-release).
Controlled release fertilizers are also referred to as sustained-release or timed-release. Many controlled release fertilizers are intended to be applied approximately every 3–6 months, depending on watering, growth rates, and other conditions, whereas water-soluble fertilizers must be applied at least every 1–2 weeks and can be applied as often as every watering if sufficiently dilute.
Unlike agricultural fertilizers, horticultural fertilizers are marketed directly to consumers and become part of retail product distribution lines.
Health and sustainability issues
In many countries there is the public perception that inorganic fertilizers “poison the soil” and result in “low quality” produce However, there is very little (if any) scientific evidence to support these views. When used appropriately, inorganic fertilizers enhance plant growth, the accumulation of organic matter, and the biological activity of the soil, thus preventing overgrazing and soil erosion. Studies in Australia show ‘biodynamic’ or ‘organic farms are less productive and less sustainable than conventional farms that used inorganic fertilisers. The nutritional value of plants for human and animal consumption is typically improved when inorganic fertilizers are used appropriately.
Many inorganic fertilizers do not replace trace mineral elements in the soil which become gradually depleted by crops. This depletion has been linked to studies which have shown a marked fall (up to 75%) in the quantities of such minerals present in fruit and vegetables. However, a recent review of 55 reputable scientific studies concluded “there is no evidence of a difference in nutrient quality between organically and conventionally produced foodstuffs”
In Western Australia deficiencies of zinc, copper, manganese, iron and molybdenum were identified as limiting the growth of broad-acre crops and pastures in the 1940s and 1950s. Soils in Western Australia are very old, highly weathered and deficient in many of the major nutrients and trace elements. Since this time these trace elements are routinely added to inorganic fertilizers used in agriculture in this state.
There are concerns regarding arsenic, cadmium and uranium accumulating in fields treated with fertilizers. The phosphate minerals contain trace amounts of these elements and if no cleaning step is applied after mining the continuous use of phosphate fertilizers leads towards an accumulation of these elements in the soil. High levels of lead and cadium can also be found in many manures or sewage sludges.
Phosphate fertilizers replace inorganic arsenic naturally found in the soil, displacing the heavy metal and causing accumulation in runoff Eventually these heavy metals can build up to unacceptable levels and build up in produce.
Another problem with inorganic fertilizers is that they are now produced in ways which cannot be continued indefinitely. Potassium and phosphorus come from mines (or saline lakes such as the Dead Sea) and such resources are limited. Nitrogen sources are effectively unlimited (forming over 70% of atmospheric gases), however, nitrogen fertilizers are presently made using fossil fuels such as natural gas and coal, which are limited.
Innovative thermal depolymerization biofuel schemes are experimenting with the production of byproducts with 9% nitrogen fertilizer from organic waste.
Organic fertilizers (‘natural’ fertilizer)
Naturally occurring organic fertilizers include manure, worm castings, peat moss, seaweed, sewage and guano. Sewage sludge use in organic agricultural operations in the U.S. has been extremely limited and rare due to USDA prohibition of the practice (due to toxic metal accumulation, among other factors.
Cover crops are also grown to enrich soil as a green manure through nitrogen fixation from the atmosphere by bacterial nodules on roots; as well as phosphorus (through nutrient mobilization) content of soils.
Processed organic fertilizers from natural sources include compost (from green waste), bloodmeal and bone meal (from organic meat production facilities), and seaweed extracts (alginates and others).
Mixed definitions of ‘organic’
There can be confusion as to the veracity of the term ‘organic’ when applied to agricultural systems and fertilizer. The problem is one of confusion of terminology between agricultural and chemical disciplines.
Minerals such as mined rock phosphate, sulfate of potash and limestone are also considered organic fertilizers, although they contain no organic (carbon) molecules. Some ambiguity in the usage of the term organic exists; however, it is simple to differentiate with a separation between the scientific and colloqial uses (as in velocity in common usage (Speed) and physics usage(Velocity)–see Velocity (disambiguation)).
Synthetic fertilizers, such as urea and urea formaldehyde, are organic in the sense of the organic chemistry definition of organic, can be supplied organically (agriculturally), but when manufactured as a pure chemical is not organic under organic certification standards
Naturally mined powdered limestone mined rock phosphate and sodium nitrate, are inorganic (in a chemical sense) in that they contain no carbon molecules, and are energetically-intensive to harvest, but are approved for organic agriculture in minimal amounts
The common thread that can be seen through these examples is that organic agriculture defines itself through minimal processing (e.g. via chemical energy such as petroleum—see Haber process), as well as being naturally-occurring (as is, or via natural biological processing such as the composting process).
Benefits of organic fertilizer
However, by their nature, organic fertilizers provide increased physical and biological storage mechanisms to soils, mitigating risks of over-fertilization. Organic fertilizer nutrient content, solubility, and nutrient release rates are typically much lower than mineral (inorganic) fertilizers. One study found that over a 140-day period, after 7 leachings:
- Organic fertilizers had released between 25% and 60% of their nitrogen content
- Controlled release fertilizers(CRFs) had a relatively constant rate of release
- Soluble fertilizer released most of its nitrogen content at the first leaching
Disadvantages of organic fertilizer
It is difficult to chemically distinguish between urea of biological origin and those produced synthetically. Like inorganic fertilisers, it is possible to over-apply organic fertilizers if does not measure and distribute the required amounts according to the recommended amounts for the plot of land in question. Release of the nutrients may happen quite suddenly depending on the type of organic fertiliser used.
Because of their dilute concentration of nutrients, transport and application costs are typically much greater for organic than inorganic fertilizers.
Organic fertilizers from treated sewage, composts and sources can be quiet variable from one batch to the next. Unless each batch is tested the amounts of nutrient applied are not precisely known.
[edit] Environmental risks of fertilizer use
High application rates of nitrogen fertilizers in order to maximize crop yields, combined with the high solubilities of these fertilizers leads to increased leaching of nitrates into groundwater The use of ammonium nitrate in inorganic fertilizers is particularly damaging, as plants absorb ammonium ions preferentially over nitrate ions, while excess nitrate ions which are not absorbed dissolve (by rain or irrigation) into groundwater. Nitrate levels above 10 mg/L (10 ppm) in groundwater can cause ‘blue baby syndrome‘ (acquired methemoglobinemia), leading to hypoxia (which can lead to coma and death if not treated)
Nitrogen-containing inorganic fertilizers in the form of nitrate and ammonium also cause soil acidification
Eventually, nitrate-enriched groundwater makes its way into lakes, bays and oceans where it accelerates the growth of algae, disrupts the normal functioning of water ecosystems, and kills fish in a process called eutrophication (which may cause water to become cloudy and/or discolored—green, yellow, brown, or red). About half of all the lakes in the United States are now eutrophic, while the number of oceanic dead zones near inhabited coastlines are increasing.
As of 2006, the application of nitrogen fertilizer is being increasingly controlled in Britain and the United States. If eutrophication can be reversed, it may take decades before the accumulated nitrates in groundwater can be broken down by natural processes.
Storage and application of some nitrogen fertilizers in some weather or soil conditions can cause emissions of the greenhouse gas nitrous oxide (N2O). Ammonia gas (NH3) may be emitted following application of ‘inorganic’ fertilizers, or manure/slurry. Besides supplying nitrogen, ammonia can also increase soil acidity (lower pH, or “souring”). Excessive nitrogen fertilizer applications can also lead to pest problems by increasing the birth rate, longevity and overall fitness of certain pests.
The concentration of up to 100 mg/kg of cadmium in phosphate minerals (for example, minerals from Nauru and the Christmas islands) increases the contamination of soil with cadmium, for example in New Zealand. Uranium is another example of a contaminant often found in phosphate fertilizers; also, radioactive Polonium-210 contained in phosphate fertilizers is absorbed by the roots of plants and stored in its tissues. Tobacco derived from plants fertilzed by rock phosphates contains Polonium-210 which emits alpha radiation estimated to cause about 11,700 lung cancer deaths each year worldwide.
For these reasons, it is recommended that knowledge of the nutrient content of the soil and nutrient requirements of the crop are carefully balanced with application of nutrients in inorganic fertilizer. This process is called nutrient budgeting. By careful monitoring of soil conditions, farmers can avoid wasting expensive fertilizers, and also avoid the potential costs of cleaning up any pollution created as a byproduct of their farming.
Hazard of over-fertilization
Over-fertilization of a vital nutrient can be as detrimental as underfertilization. “Fertilizer burn” can occur when too much fertilizer is applied, resulting in a drying out of the roots and damage or even death of the plant. According to UC IPM, all organic fertilizers, and some specially-formulated inorganic fertilizers are classified as ’slow-release’ fertilizers, and therefore cannot cause nitrogen burn. Organic fertilizers are as likely to cause plant burn as inorganic fertilizers.
If excess nitrogen is present, some plants can exude the excess through their leaves in a process called guttation
Environmental toxicity of fertilizer
Toxic fertilizers are recycled industrial waste that introduce several classes of toxic materials into farm land, garden soils, and water streams. The consumption levels of toxic fertilizer are increasing lately in the U.S. from citizens who are purchasing the wrong chemicals for their gardens as well as choosing the wrong company to purchase it from.
This is leading to major environmental problems due to the fact of toxic waste being processed and planted into our land and water. The most common toxic elements in this type of fertilizer are mercury, lead, and arsenic.
Between 1990-1995, 600 companies from 44 different states sent 270 million pounds of toxic waste to farms and fertilizer companies across the country
According to the United States Food and Drug Administration:
“Current information indicates that only a relatively small percentage of fertilizers is manufactured using industrial wastes as ingredients, and that hazardous wastes are used as ingredients in only a small portion of waste-derived fertilizers.”
and
“[the] EPA has continually encouraged the beneficial reuse and recycling of industrial wastes.”
Heavy metal content of recycled fertilizer
Steel industry wastes, recycled into fertilizers for their high levels of zinc (essential to plant growth), wastes can include the following toxic metals:
Toxic organic compounds
Dioxins, polychlorinated dibenzo-p-dioxins (PCDDs), and polychlorinated dibenzofurans (PCDFs) have been detected in fertilizers and soil amendments
Global issues
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We throw away nutrients for our plants in underground sewage systems. We do this in such a way that pollutes underground water tables. Then we buy manufactured “nutrients” for our plants which aren’t as good as what we threw away. This is modern day wastewater “technology”.
Michael Reynolds – Earthship Vol.2: Systems and Components |
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The growth of the world’s population to its current figure has only been possible through intensification of agriculture associated with the use of fertilizers.There is an impact on the sustainable consumption of other global resources as a consequence.
The use of fertilizers on a global scale emits significant quantities of greenhouse gas into the atmosphere. Emissions come about through the use of:
By changing processes and procedures, it is possible to mitigate some, but not all, of these effects on anthropogenic climate change.
The nitrogen-rich compounds found in fertilizer run-off is the primary cause of a serious depletion of oxygen in many parts of the ocean, especially in coastal zones; the resulting lack of dissolved oxygen is greatly reducing the ability of these areas to sustain oceanic fauna. Anoxic respiration by bacteria in the eutrophicated marine zones also releases nitrous oxide to the atmosphere. Through the increasing use of nitrogen fertiliser, which is added at a rate of 120 million tons per year presently to the already existing amount of reactive nitrogen, nitrous oxide has become the third most important greenhouse gas after carbon dioxide and methane, with a global warming potential 296 times larger than an equal mass of carbon dioxide, while it also contributes to stratospheric ozone depletion.
The mining of phosphorus for fertiliser uses leads to the depletion of the global (fossil) phosphate resources. It is unclear whether peak phosphorus has already been passed or has yet to come.
See also
Was that enough info for you? Hope this helped you on your journey to a perfect garden! 1-866-PGS-GROW
Figure one: Water heaters (left) are useful for heating nutrient in winter. In summer, ‘water-chillers’ (right are effective for cooling. These items can be thermostically controlled.
Figure two: Root browning is a typical symptom of the root diesase ‘pythium’.
Figure three: A ‘raised’ lid permits airflow within the reservoir whilst still preventing light and dirt ingress and evaporation. Airflow helps prevent stale air and fungus/moulds.
Figure four: Air stones are a reliable method of ensuring oxygen levels are adequate.
Chemical properties of Humic substances. (Stevenson 1982)
Model structure of fulvic acid. (by Buffle)
Model structure of humic acid. (Stevenson 1982)
Dr. Merle H. Jensen is Assistant Dean for Sponsored Research and Associate Director of the Arizona Agricultural Experiment Station at the University of Arizona and Professor of Plant Science. He is a graduate of California State Polytechnic, Cornell and Rutgers Universities. He has been involved with numerous programs for research and development of new methods of food production, including serving as team leader to develop the agricultural systems for “The Land” at EPCOT, Walt Disney World and helped researchers at NASA.
Dr. Jensen is one of America’s leading agricultural scientists on the subject of controlled environment agriculture and future opportunitiesfor food production. He has published nearly 100 research and technical articles, and his research and development projects have been featured in many popular publications and television programs.
Boris,
Ideal temps for hydro is 18 to 27 degrees C. Try experimenting with temperatures and see for yourself the effects. 
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