What is Peat?

1. What is Peat?

Peat is an organic fossil formed as a result of dying-off and incomplete decay of moor plants in conditions of increased moisture with a lack of oxygen which is the first stage in transformation of plant material into coal.

2. Botanical composition of peat – the amount of residues of peat-forming plants composing peat vegetable fiber is denoted by the letter R and is expressed in %. Each type of peat is characterized by a certain type of vegetation. Using a microscope, all plant residues that form a certain peat can be determined. Then the name is given, for example, sedge low moor, sedge-sphagnum, sphagnum high moor, etc.

​3. Humiditythe amount of water expressed as a percentage of the total mass. It is denoted as W and is expressed in %. In its natural occurrence, humidity can reach up to 95%. With various methods of peat extraction (mechanical or vacuum), peat moisture content ranges from 45 to 65%.

​ The most acceptable for the preparation of substrates is a humidity of 50...60%. Such peat nourishes water well and will hold it for a certain time. If humidity is below 45%, then peat saturation requires a certain time.

​4. Acidity – the capability of peat to exhibit the properties of acids and alkalis when interacting with water or salt solutions. It is determined by the degree of concentration of hydrogen ions (pH units).

​ Depending on the state of H+ ions in peat, active and exchange acidity is distinguished.

​ Active acidity is associated with the presence of hydrogen ions in the soil solution. It is due to the presence of carbon dioxide, acids and salts, as well as organic acids formed during the decomposition of organic matter. Active acidity is determined by the pH value in the aqueous extract.

​ Exchange acidity is caused by the presence of hydrogen and aluminum ions capable of the exchange, in the absorption complex. Exchange acidity is a more mobile part of hydrogen ions which can be converted into a solution by treating peat with a solution of a neutral salt of potassium chloride.

Types of acidity:

  • high 0-3
  • slight 4-6
  • neutral 7
  • slightly alkaline 8-10
  • strongly alkaline 11-14

​ When pH = 5.5...6.5, it means that exchange acidity (pHKCl) should not be lower than 5.5 pH units, and active acidity (pHH2O) should not exceed 6.5 pH units.

​ To bring acidity to the required indicators, lime materials are used – slaked limestone (dolomite) flour, chalk.

​ The neutralization period occurs in the first minutes of mixing and may continue over time, depending on temperature, for 5-10 days.

​​5. Electrical conductivity (EU) – the ability of a material to pass an electric current through itself. Conductivity is the reciprocal of resistance. It is expressed in mS/cm. By the electrical conductivity of the extract, one can determine the concentration of dissolved salts in the solution. Moreover, all salts in the solution are measured, not just fertilizer salts.

There is an optimal value of electrical conductivity for each plant. The optimum electrical conductivity of the substrate ranges from 0.8...1.5 mS/cm.

​​Electrical conductivity of the substrate affects the capability of nutrients to be absorbed by plants. A high EC level is associated with poor growth of shoots and roots, as well as the appearance of root rot. A low EC level leads to a slowed growth of plants; the leaves begin to turn yellow.

​​​6. Bulk density – the ratio of the substance mass to the volume it takes denoted by ρ, kg/m3. Bulk density can be at actual or at conditional humidity. Humidity of 40% is considered to be relative humidity.

​Bulk density of transitional peat is low, 150-200 kg/m3. This feature of peat facilitates the work with it in greenhouses.

​​​​7. Ash content – the ratio of the peat mineral part mass remaining after calcination to the dry peat mass. It is usually expressed in % of the analyzed sample mass and is denoted as A.

​​Ash content depends on the botanical composition. Low-ash content sphagnum mosses (high moor peat) has an ash content of 2.0...4.0%, and wood residues and sedge (transitional, low moor peat) has that of 4.5 to 20%. Ash content increases with increasing degree of decomposition.

​​Peat with an ash content of not more than 15% is used for the production of peat nutritious substrates.

​​​​​8. Fractional composition – quantitative distribution of particles in the sample depending on the size, expressed as a percentage by the product mass passing through a sieve (set of sieves) or remaining on each sieve (set of sieves).

​​​​​9. Peat impurity – mass fraction of impurities in peat. Foreign impurities include: wood chips, pieces of rhizomes, pieces of peat of low degree of decomposition, peat tirr, etc.