Ultimately, fertilisers are based on nutrient solutions that have been used in plant nutrition for a long time. However, depending on the intended use (whether NPK fertilisers used in agriculture and horticulture or fertilisers used in garden centres and other crops), they have very different compositions. What they have in common is that they have the task of ensuring a continuous supply of the required nutrients.
As early as 1840, the Giessen chemist JUSTUS v. LIEBIG (1803-1873) demonstrated the importance of mineral components derived from the decomposition of plant and animal remains in his work "Organic Chemistry in its Application to Agriculture and Physiology".
Ultimately, fertilisers are based on nutrient solutions that have been used in plant nutrition for a long time. However, depending on the intended use (whether NPK fertilisers used in agriculture and horticulture or fertilisers used in garden centres and other crops), they have very different compositions. What they have in common is that they have the task of ensuring a continuous supply of the required nutrients.
As early as 1840, the Giessen chemist JUSTUS v. LIEBIG (1803-1873) demonstrated the importance of mineral components derived from the decomposition of plant and animal remains in his work "Organic Chemistry in its Application to Agriculture and Physiology".
He came to the conclusion that plants have an abundance of carbon, hydrogen, oxygen and nitrogen, making the addition of these substances through fertilisation superfluous. KARL SPRENGEL also proved that certain, albeit extremely small, quantities of mineral components are just as important for plants to live and thrive.
The first synthetic nutrient solution was produced by J. v. SACHS in collaboration with the chemist J. A. STÖCKHARDT. It contained 1 g potassium nitrate, 0.5 g calcium sulphate, 0.4 g magnesium sulphate, 0.5 g calcium hydrogen phosphate and a trace of iron (III) chloride per 1000 ml water.
In 1861, J. A. L. W. KNOP developed the Knop nutrient solution named after him, which is still widely used today: it contains 1 g calcium nitrate, 0.25 g magnesium sulphate, 0.25 g potassium dihydrogen phosphate, 0.25 g potassium nitrate and a trace of iron sulphate per 1000 ml water.
The lack of one of the elements cannot be compensated for by an excess of another (chemically close to it). Atmospheric nitrogen, metallic potassium or elemental sulphur cannot be utilised either. The respective ions are required.
However, this does not cover all the elements required by a plant. The trace elements, for which SPRENGEL has already provided indirect evidence, are still missing.
R. D. HOAGLAND (1884-1949) compiled a solution of trace elements, 1 ml of which should be added to one of the standard nutrient solutions: The following are dissolved in 18 l of water: 0.5 g lithium chloride, 1 g copper sulphate, 1 g zinc sulphate, 11 g boric acid, 1 g aluminium sulphate, 0.5 g tin chloride, 7 g magnesium chloride, 1 g nickel sulphate, 1 g cobalt nitrate, 0.5 g potassium iodide, 1 g titanium oxide, 0.5 g potassium bromide. This trace element solution, also known as A-Z, covers most of the trace elements required by organisms. According to current opinion, at least boron, copper, manganese, zinc and molybdenum are fundamentally required. However, there are certainly indications that other trace elements such as molybdenum, zinc or cobalt (for the synthesis of vitamin B12) are required by some organisms.
In the aquarium hobby, the situation is different for "normal" planted community tanks in that nitrogen (mainly in the form of nitrate) and phosphorus (in the form of phosphate) are usually present in sufficient quantities, if not in excess. The main source of these two elements is fish food, which is at least partially supplied to the aquatic plants via the animal. These elements are therefore generally not required in aquatic plant fertilisers for aquaria (with the exception of heavily plant-dominated aquaria with few fish). However, the other trace elements required are very often deficient substances that should be added in order to achieve and maintain stable, vigorous plant growth.
Good aquatic plant fertilisers for community aquariums, such as the Fermendo system, are therefore free from nitrogen and phosphorus and are based on the composition of HOAGLAND's A-Z solution.
Source information:
Nutrient salts at www.biologie.uni-hamburg.de
Knop's nutrient solution at www.biologie-lexikon.de