The Hoagland solution is a hydroponic nutrient solution that was newly developed by Hoagland and Snyder in 1933, [1] modified by Hoagland and Arnon in 1938, [2] and revised by Arnon in 1950. [3] It is one of the most popular standard solution compositions for growing plants, in the scientific world at least, with more than 20,000 citations listed by Google Scholar. [4] The Hoagland solution provides all essential elements for plant nutrition and is appropriate for supporting normal growth of a large variety of plant species. [5]
The artificial solution described by Dennis Hoagland in 1933, [1] known as Hoagland solution (0), has been modified several times, mainly to add ferric chelates to keep iron effectively in solution, [6] and to optimize the composition and concentration of other trace elements, some of which are not generally credited with a function in plant nutrition. [7] In Hoagland's nutrient recipes of 1938, referred to as Hoagland solution (1, 2), the number of trace elements was subsequently reduced to the generally accepted essential elements (B, Mn, Zn, Cu, Mo, Fe, and Cl). [2] Later research confirmed that their concentrations had been adjusted for optimal plant growth. [8]
In Arnon's revision of 1950, only one concentration (Mo 0.011 ppm) was changed compared to 1938 (Mo 0.048 ppm), while the concentration of macronutrients of the Hoagland solutions (0), (1), and (2) remained the same since 1933, with the exception of calcium (160 ppm) in solution (2). [3] The main difference between solution (1) and solution (2) is the different use of nitrate-nitrogen and ammonium-nitrogen based stock solutions to prepare the respective Hoagland solution of interest. Accordingly, the original 1933 and the modified concentrations of 1938 and 1950 for each essential element and sodium are shown below, the calculation of the latter values being derived from Tables 1 and 2: [9]
Plant nutrients are usually absorbed from the soil solution. [10] The Hoagland solution, originally intended to imitate a (nutrient-) rich soil solution, [11] has high concentrations of N and K so it is very well suited for the development of large plants like tomato and bell pepper. [12] For example, a half-strength macronutrient solution (1) of Hoagland can be combined with a full micronutrient solution of Long Ashton and a tenth-strength ferric EDTA solution to fertilize tomato seedlings. [13] Due to relatively high concentrations in the aqueous stock solutions (cf. Tables 1 and 2) the Hoagland solution is very good for the growth of plants with lower nutrient demands as well, such as lettuce and aquatic plants, with the further dilution of the preparation to 1⁄4 or 1⁄5 of the modified solution. [14]
Salts, acids and complex ions to make up the Hoagland hydroponic solution formulations (1) and (2): [15]
To prepare the stock solutions and a full Hoagland solution (1) [2]
Component | Quantities in solution | |
---|---|---|
g/L | mL/L | |
Macronutrients | ||
2M KNO3 | 202 | 2.5 |
2M Ca(NO3)2•4H2O | 472 | 2.5 |
2M MgSO4•7H2O | 493 | 1 |
1M KH2PO4 | 136 | 1 |
Micronutrients | ||
H3BO3 | 2.86 | 1 |
MnCl2•4H2O | 1.81 | 1 |
ZnSO4•7H2O | 0.22 | 1 |
CuSO4•5H2O | 0.08 | 1 |
H2MoO4•H2O, or | 0.09 | 1 |
Na2MoO4•2H2O | 0.12 | 1 |
Iron | ||
C12H12Fe2O18, or Sprint 138 iron chelate* | 5 15 | 1 1.5 |
To prepare the stock solutions and a full Hoagland solution (2) [3]
Component | Quantities in solution | |
---|---|---|
g/L | mL/L | |
Macronutrients | ||
2M KNO3 | 202 | 3 |
2M Ca(NO3)2•4H2O | 472 | 2 |
2M MgSO4•7H2O | 493 | 1 |
1M NH4H2PO4 | 115 | 1 |
Micronutrients | ||
H3BO3 | 2.86 | 1 |
MnCl2•4H2O | 1.81 | 1 |
ZnSO4•7H2O | 0.22 | 1 |
CuSO4•5H2O | 0.08 | 1 |
H2MoO4•H2O | 0.02 | 1 |
Iron | ||
C12H12Fe2O18, or Sprint 138 iron chelate* | 5 15 | 1 1.5 |
Sprint 138 iron chelate is produced as Na-Fe-EDDHA (C18H16FeN2NaO6), while Hoagland's original solution formulations contain ferric tartrate (C12H12Fe2O18), but no sodium ions. [1] [2] [3] Synthesizing a sodium-free ferric EDTA complex (C10H12FeN2O8−) in a laboratory is sometimes preferred to buying ready-made products. [6] [9] Variable micronutrients (e.g., Co, Ni) and rather non-essential elements (e.g., Pb, Hg) mentioned in Hoagland's 1933 publication [1] (known as "A-Z solutions a and b" [16] ) are no longer included in his later circulars. [2] [3] Most of these metallic elements, as well as organic compounds, are not necessary for normal plant nutrition. [17] As an exception, there is evidence that, for example, some algae require cobalt for the synthesis of vitamin B12. [18]
Hydroponics is a type of horticulture and a subset of hydroculture which involves growing plants, usually crops or medicinal plants, without soil, by using water-based mineral nutrient solutions in an artificial environment. Terrestrial or aquatic plants may grow freely with their roots exposed to the nutritious liquid or the roots may be mechanically supported by an inert medium such as perlite, gravel, or other substrates.
Nitrate is a polyatomic ion with the chemical formula NO−
3. Salts containing this ion are called nitrates. Nitrates are common components of fertilizers and explosives. Almost all inorganic nitrates are soluble in water. An example of an insoluble nitrate is bismuth oxynitrate.
A fertilizer or fertiliser is any material of natural or synthetic origin that is applied to soil or to plant tissues to supply plant nutrients. Fertilizers may be distinct from liming materials or other non-nutrient soil amendments. Many sources of fertilizer exist, both natural and industrially produced. For most modern agricultural practices, fertilization focuses on three main macro nutrients: nitrogen (N), phosphorus (P), and potassium (K) with occasional addition of supplements like rock flour for micronutrients. Farmers apply these fertilizers in a variety of ways: through dry or pelletized or liquid application processes, using large agricultural equipment, or hand-tool methods.
Chelation is a type of bonding of ions and their molecules to metal ions. It involves the formation or presence of two or more separate coordinate bonds between a polydentate ligand and a single central metal atom. These ligands are called chelants, chelators, chelating agents, or sequestering agents. They are usually organic compounds, but this is not a necessity.
Ethylenediaminetetraacetic acid (EDTA), also called EDTA acid after its own abbreviation, is an aminopolycarboxylic acid with the formula [CH2N(CH2CO2H)2]2. This white, water-insoluble solid is widely used to bind to iron (Fe2+/Fe3+) and calcium ions (Ca2+), forming water-soluble complexes even at neutral pH. It is thus used to dissolve Fe- and Ca-containing scale as well as to deliver iron ions under conditions where its oxides are insoluble. EDTA is available as several salts, notably disodium EDTA, sodium calcium edetate, and tetrasodium EDTA, but these all function similarly.
Magnesium sulfate or magnesium sulphate is a chemical compound, a salt with the formula MgSO4, consisting of magnesium cations Mg2+ (20.19% by mass) and sulfate anions SO2−4. It is a white crystalline solid, soluble in water but not in ethanol.
Plant nutrition is the study of the chemical elements and compounds necessary for plant growth and reproduction, plant metabolism and their external supply. In its absence the plant is unable to complete a normal life cycle, or that the element is part of some essential plant constituent or metabolite. This is in accordance with Justus von Liebig's law of the minimum. The total essential plant nutrients include seventeen different elements: carbon, oxygen and hydrogen which are absorbed from the air, whereas other nutrients including nitrogen are typically obtained from the soil.
Long Ashton Research Station (LARS) was an agricultural and horticultural government-funded research centre located in the village of Long Ashton near Bristol, UK. It was created in 1903 to study and improve the West Country cider industry and became part of the University of Bristol in 1912. Later, it expanded into fruit research and in the 1980s was redirected to work on arable crops and aspects of botany. It closed in 2003.
Murashige and Skoog medium is the most popular plant growth medium used in the laboratories worldwide for cultivation of plant cell culture.
Deep water culture (DWC) is a hydroponic method of plant production by means of suspending the plant roots in a solution of nutrient-rich, oxygenated water. Also known as deep flow technique (DFT), floating raft technology (FRT), or raceway, this method uses a rectangular tank less than one foot deep filled with a nutrient-rich solution with plants floating in Styrofoam boards on top. This method of floating the boards on the nutrient solution creates a near friction-less conveyor belt of floating rafts. DWC, along with nutrient film technique (NFT), and aggregate culture, is considered to be one of the most common hydroponic systems used today. Typically, DWC is used to grow short-term, non-fruiting crops such as leafy greens and herbs. DWC was invented accidentally in 1998 by a legacy cannabis grower who goes by the name of “Snype”. This occurred because “Snype” and his (unnamed) associate had to take a trip to Amsterdam and needed a way to feed their cannabis crop while they were away. They built nutrient and water reservoirs that would keep the plants thoroughly fed in their absence, and thusly the DWC system was born. They revised this system in 2010 to create RDWC. The large volume of water helps mitigate rapid changes in temperature, pH, electrical conductivity (EC), and nutrient solution composition.
A grow box is a partially or completely enclosed system for raising plants indoors or in small areas. Grow boxes are used for a number of reasons, including the lack of available outdoor space or the desire to grow vegetables, herbs or flowers during cold weather months. They can also help protect plants against pests or diseases.
Chelates in animal feed is jargon for metalloorganic compounds added to animal feed. The compounds provide sources of various metals that improve the health or marketability of the animal. Typical metals salts are derived from cobalt, copper, iron, manganese, and zinc. The objective of supplementation with trace minerals is to avoid a variety of deficiency diseases. Trace minerals carry out key functions in relation to many metabolic processes, most notably as cofactors for enzymes and hormones, and are essential for optimum health, growth and productivity. For example, supplementary minerals help ensure good growth, bone development, feathering in birds, hoof, skin and hair quality in mammals, enzyme structure and functions, and appetite. Deficiency of trace minerals affect many metabolic processes and so may be manifested by different symptoms, such as poor growth and appetite, reproductive failures, impaired immune responses, and general ill-thrift. From the 1950s to the 1990s most trace mineral supplementation of animal diets was in the form of inorganic minerals, and these largely eradicated associated deficiency diseases in farm animals. The role in fertility and reproductive diseases of dairy cattle highlights that organic forms of Zn are retained better than inorganic sources and so may provide greater benefit in disease prevention, notably mastitis and lameness.
Wood ash is the powdery residue remaining after the combustion of wood, such as burning wood in a fireplace, bonfire, or an industrial power plant. It is largely composed of calcium compounds, along with other non-combustible trace elements present in the wood, and has been used for many purposes throughout history.
Johann August Ludwig Wilhelm Knop was a German agrochemist and co-founder of modern water culture due to his pioneering experiments with the cultivation of crops in nutrient solutions.
Daniel Israel Arnon was a Polish-born American plant physiologist and National Medal of Science recipient whose research led to greater insights into the operation of photosynthesis and nutrition in plants.
Arthur Wallace, was a soil scientist.
Organic hydroponics is a hydroponics culture system based on organic agriculture concepts that does not use synthetic inputs such as fertilizers or pesticides. In organic hydroponics, nutrient solutions are derived from plant and animal material or naturally mined substances. Most studies on the topic have focused on the use of organic fertilizer.
Dennis Robert Hoagland was an American chemist and plant and soil scientist who pioneered work in plant nutrition, soil chemistry, agricultural chemistry, biochemistry, and physiology. He was Professor of Plant Nutrition at the University of California at Berkeley from 1927 until his death in 1949.
Ferric EDTA is the coordination complex formed from ferric ions and EDTA. EDTA has a high affinity for ferric ions. It gives yellowish aqueous solutions.
Seventeen elements or nutrients are essential for plant growth and reproduction. They are carbon (C), hydrogen (H), oxygen (O), nitrogen (N), phosphorus (P), potassium (K), sulfur (S), calcium (Ca), magnesium (Mg), iron (Fe), boron (B), manganese (Mn), copper (Cu), zinc (Zn), molybdenum (Mo), nickel (Ni) and chlorine (Cl). Nutrients required for plants to complete their life cycle are considered essential nutrients. Nutrients that enhance the growth of plants but are not necessary to complete the plant's life cycle are considered non-essential, although some of them, such as silicon (Si), have been shown to improve nutrent availability, hence the use of stinging nettle and horsetail macerations in Biodynamic agriculture. With the exception of carbon, hydrogen and oxygen, which are supplied by carbon dioxide and water, and nitrogen, provided through nitrogen fixation, the nutrients derive originally from the mineral component of the soil. The Law of the Minimum expresses that when the available form of a nutrient is not in enough proportion in the soil solution, then other nutrients cannot be taken up at an optimum rate by a plant. A particular nutrient ratio of the soil solution is thus mandatory for optimizing plant growth, a value which might differ from nutrient ratios calculated from plant composition.