Sapropel (from the Greek sapros – rotten and pelos – mud, silt) – bottom sediments of freshwater reservoirs, from pink to dark brown in color, the natural color changes in the air. It is organomineral compounds. Sapropel is formed from the remains of plants and animals, contains mineral and organic impurities, dries slowly, after drying it becomes solid and does not get wet again. It contains humic acids, fulvic acids, hemicellulose, cellulose, bitumen, ash (on average 20-60%).
The sapropel reserves in Russia are estimated at 92 billion tons in terms of 60% moisture, in the Republic of Belarus – 2,76 billion m3.
Sapropel is extracted by dredgers with pulp filling in settling tanks; during the first year it is dehydrated, while during the second year it is dried after freezing, which promotes its loosening, and then it becomes a loose mass with approximately 50% humidity. In the first year it is possible to apply directly to the fields, where after freezing and natural drying it turns into a loose mass of moisture of about 80%.
- Mineral fertilizers
- Microfertilizers
- Complex fertilizers
- Organic fertilizers
Chemical composition of sapropel
The composition of the organic mass of sapropel, depending on the deposits is: humic acids – 11.3-43.4%, fulvic acids – 2.1-23.5%, non-hydrolysable residue – 5.1-22.6%, hemicellulose – 9.8-52.5%, cellulose – 0.4-6%, water-soluble matter – 2.4-13.5%, bitumen A – 3.4-10.9%, bitumen C – 2.1-6.6%, total nitrogen – 0.6-2.6%, phosphorus – 0.14-0.19%, calcium – 2.5-43.8%, magnesium – 0.3-2.3%. The content of organic matter – from 12 to 80%, ash – from 19 to 88% (in dry matter), including up to 20-30% of calcium and magnesium carbonates. The technical conditions regulate the requirements for sapropel fertilizers.
Table. Physical and chemical characteristics of sapropel fertilizers[1]Agrochemistry. Textbook / V.G. Mineev, V.G. Sychev, G.P. Gamzikov et al; ed. by V.G. Mineev. - M.: Publishing house of the All-Russian Scientific Research Institute named after D.N. Pryanishnikov, … Continue reading
| Mass fraction of particles larger than 10 mm, %, max | |||
| Mass fraction of moisture, %, max | |||
| Ash content, %, max | |||
| Mass fraction of total nitrogen, % per dry product, not less | |||
| Exchangeable acidity, pH, not less | |||
| Mass fraction of calcium oxide, %, not less | |||
| Specific activity of radionuclides (cesium 137), Bq/kg | |||
Nitrogenous substances of sapropel are presented in high-molecular compounds, so the forms of nitrogen and phosphorus available for plants are 2-3 times less than in manure, potassium – a negligible amount.
Sapropel contains a large number of trace elements in 1 kg of dry matter: 200-1000 mg of manganese, 10-400 mg of zinc, 10-200 mg of boron, 2-60 mg of copper and 1-20 mg of molybdenum. Depending on the location of the reservoir can contain large amounts of heavy metals.
The composition of the sapropel can vary greatly depending on the location of even one body of water.
Table. Average composition of various sapropels (from different sources)[2] Yagodin B.A., Zhukov Yu.P., Kobzarenko V.I. Agrochemistry / Edited by B.A. Yagodin. - Moscow: Kolos, 2002. - 584 p.: ill.
| Low ash | ||||||
| Medium ash | ||||||
| Increased ash: | ||||||
| - clay, sandy | ||||||
| - lime | ||||||
| High ash (lake lime) | ||||||
| Silt: | ||||||
| - clay, sandy | ||||||
| - lime | ||||||
Classification
Depending on the content of silica (SiO2) and calcium oxide (CaO) sapropels are divided into:
- organic – with ash content less than 30%;
- siliceous – with more than 50% silica;
- calcareous (limey) – with a content of calcium oxide of more than 30%;
- mixed.
Calcareous sapropels are also used as lime fertilizer, not inferior to chalk and dolomite flour.
According to A.Y. Rubinstein’s classification, sapropels are divided by ash content into:
- low ash – with ash content up to 30%;
- medium ash – with ash content 30-50%;
- increased ash content up to 70%;
- high ash – with ash content 70-85%;
- silt – with ash content over 85%.
Sapropel application
According to the generalized data of the All-Russian Institute of Fertilizers and Agrochemistry field experiments, sapropel shows a relatively low efficiency: to obtain crop yield increases comparable to those from manure, sapropel doses should be on average 3 times higher.
Sapropel has some positive properties: high water-holding and low filtration capacity, which improves water-physical properties of light soils. At the expense of adhesive ability sapropel at interaction with soil improves the structure, gives lumpiness, friability, increases air permeability.
Sapropel can be used as an organic fertilizer and in composts with manure, slurry, feces.
The timing of application and methods of laying sapropel under crops does not differ from other organic fertilizers. Sapropel fertilizer is not necessary to embed in the soil immediately after distribution on the field, it is acceptable to make embedding after 3-7 days. Sapropel better suited for sandy and sandy loam soils, as their effectiveness is higher than on soils with heavy granulometric composition.
By its fertilizer value, 1 t of sapropel is equal to 0,6-0,7 t of peat-manure compost. The use of sapropel as a local fertilizer is connected with the costs of its extraction, transportation and application. It is economically justified to transport sapropel to a distance of up to 20 km.
Sapropel is made under crops in the rates which are determined for each field, based on conditions, biological characteristics of crops, agrochemical characteristics of fertilizer. It is best to determine the rates of sapropel by its equivalent content of nutrients, especially nitrogen.
Sapropel is made in doses of 30-40 tons / ha for cereal crops, 50-100 tons / ha – for vegetable crops. It is often used when there is a lack of manure and in the fields, located near the extraction sites.
Sources
Yagodin B.A., Zhukov Y.P., Kobzarenko V.I. Agrochemistry/Under ed. B.A. Yagodin. – M.: Kolos, 2002. – 584 p.: ill.
Agrochemistry. Textbook / V.G. Mineev, V.G. Sychev, G.P. Gamzikov et al. – M.: Publishing house of the All-Russian Scientific Research Institute named after D.N. Pryanishnikov, 2017. – 854 с.