Lime fertilizers – materials and mixtures of substances containing compounds (carbonates, hydroxides, oxides) of calcium, sometimes magnesium, used for liming acidic soils and as a source of calcium and magnesium in plant nutrition.
Lime fertilizers are subdivided into:
- solid lime rocks, suitable for use after milling or roasting;
- soft limestone rocks;
- industrial wastes, with a high lime content.
Importance of liming
Solid carbonate rocks, depending on their calcium and magnesium content, are divided into:
- limestones (50-56% CaO, 0.9% MgO),
- dolomitized limestones (42-55% СаО, 0.9-9.0% MgO),
- dolomites (30-32% СаО, 18-20% MgO).
Depending on the content of impurities (clay, sand) lime fertilizers are divided into:
- pure with impurities up to 5% (dolomite, limestone);
- marl or sandy with an admixture of 5 to 25%;
- marl, or sandy with an admixture of 25 to 50%; – marl, or sandy with an admixture of 25 to 50%.
The use of calcareous rocks with impurities over 15-20% is reasonable in the absence of cleaner materials. The effect of fertilizers with high impurity content is slow.
Soft lime rocks include lime tuffs containing 80-98% СаСO3; lake lime, or lake lime – 80-95% СаСO3.
Industrial waste include: shale ash with 30-50% СаО, 1,5-4,0% MgO; defekat – 60-75% СаСO3 and 10-15% of organic matter with admixtures of nitrogen, phosphorus and potassium-containing substances.
The main lime fertilizers include limestone, the proportion of calcium and magnesium in which is 75-100% CaCO3.
Limestone and dolomite flour, lime tuff, chalk and other carbonate forms of lime fertilizer can be applied simultaneously with manure, peat or compost, mixed or composted with organic fertilizers. There is no loss of nitrogen.
Ammonia forms of nitrogen fertilizers can be mixed with carbonate forms of lime fertilizers to improve their physical properties. Calcium fertilizers containing calcium and magnesium oxides and hydroxides are not allowed to mix with ammonia forms of nitrogen fertilizers because of the large losses of nitrogen.
The need for lime fertilizers is often covered by local resources – lime-containing industrial waste or local deposits of carbonate rocks. In most cases it is loose chalk, lime tuffs, lake lime, dolomite flour. However, in Russia as a whole, local lime materials and lime-containing industrial wastes do not play a large role in the balance of lime fertilizers.
Limestone and dolomite flour
Limestone and dolomite flour is obtained by crushing and grinding limestone and dolomite. In Russia (in accordance with GOST 14050-78), limestone flour is produced in two classes and two varieties, in dusty with a moisture content of up to 1.5% and weakly dusty (4-6% moisture) forms. Grades of flour are distinguished by the neutralizing ability: I grade not less than 88%, II grade – not less than 85% CaCO3. According to granulometric composition – the first class is finer grinding than the second. Classes within the grades differ in particle size distribution, the second class is finer than the first, the fractions differ: < 0.25 mm by 5-10%, < 1 mm by 3-10%.
The main component of limestone is calcium carbonate CaCO3, often including up to 10-15% MgO in the form of magnesium carbonate. The presence of MgCO3 increases the hardness of dolomitized limestone. White, gray, yellowish and brownish colors of limestone are due to impurities, which may include organic substances, various compounds of iron and manganese.
Pure dolomites consist of calcium carbonate (up to 54.4% CaCO3) and magnesium carbonate (up to 45.6%).
According to field experiments, summarized by the All-Russian Institute of Fertilizers and Agrochemistry, on average for five years, showed that the most effective is finely ground, that is less than 0.25 mm, fraction of limestone flour. This is explained by the fact that the coarse fraction reacts more slowly with the soil, so in the first years after application contributes little to improve soil properties.
Decrease in the effectiveness of limestone flour with an increase in the proportion of particles larger than 0.25 mm, increases with the transition from pure limestone to dolomitized, that is, to more hard grindable rocks.
Table. Efficiency of lime flour fractions of different granulometric composition (according to the recommendations of the All-Russian Institute of Fertilizers and Agrochemistry, 1992)
Dolomitized limestone with the content of 79-109% of the active substance in terms of CaCO3 can be used in crop rotations, saturated with legumes, potatoes, flax, root crops, as well as on heavily ashed soils.
Dolomite and magnesium limestone flour in the first place is advisable to use on light soils with a granulometric composition.
Magnesium-containing lime materials are optimal forms of lime fertilizers in crop rotations with flax, potatoes and lupine.
Industrial wastes as lime fertilizers take the second place by total volume of application in Russia. They are often as effective as lime flour.
Economically, the use of industrial waste is often more profitable, since there are no costs for extraction and processing. Ecologically, industrial waste is more appropriate, provided there are no dangerous impurities, than industrial lime fertilizers.
Many wastes from various industries, such as cement dust, waste from pulp and paper mills and factories, soda, soap, leather and other industries, containing calcium oxide, hydroxide, carbonate or silicate can be used as lime fertilizer if there are no hazardous impurities.
Dust from kilns and cement plants with CaCO3 content of more than 60% is used in farms located near cement plants. These materials by machines with closed containers and with pneumatic devices.
Cement dust contains significant impurities of potassium, has a fine particle size distribution and is a fast-acting lime fertilizer. It is effective on soils poor in mobile potassium and for crops sensitive to potassium deficiency.
Burnt and slaked lime
Burnt lime contains more than 170% CaCO3 and is a fast-acting lime fertilizer. It is made by roasting carbonate rocks according to the reaction:
CaCO3 ⋅ MgCO3 → CaO + MgO + 2CO2.
During long-term storage calcium and magnesium oxides absorb moisture and form hydroxides of calcium and magnesium – slaked lime, powdery lime:
CaO + H2O = Ca(OH)2.
Solubility of Ca (OH)2 is much higher than CaCO3, (Mg (OH)2 in water is poorly soluble), so in the first years after making slaked lime more effective than limestone meal, but in subsequent periods of their action is aligned, the duration of after action is less because of the rapid washout of calcium.
Slaked lime contains up to 135% in recalculation on CaCO3, is received as a waste product in lime plants, as well as in the manufacture of bleached lime.
Neutralizing capacity of 1 ton of Ca(OH)2 corresponds to 1.35 tons of CaCO3.
Oil shale ash is produced by burning oil shale. It contains 30-40% CaO, 1.5-3.8% MgO, impurities of compounds of potassium, sodium, phosphorus, sulfur, some microelements. It is a dust-like material and is used in the Baltic States and Belarus.
According to Russian normative requirements (TU 46-7-71) for shale ash:
- neutralizing capacity should be not less than 60% CaCO3;
- moisture content no more than 2%;
- by particle size distribution 97% of the mass must be less than 1 mm.
Most of the calcium and magnesium in the ash is contained in the form of silicic acid forms, which are less soluble than CaCO3, so the neutralization of acidity is much slower. Even at high doses (20 t/ha) ash has a positive effect on crops poorly tolerant to excess calcium (flax, potatoes).
Defecation mud (defecate)
Defecation mud, or defecate, is a waste product from sugar beet factories containing CaCO3 and Ca(OH)2.
According to the Russian regulatory documents (TU 570-74) defecate of the first class is subject to the requirements:
- neutralizing ability should correspond to the content of CaCO3 not less than 60%;
- moisture content – no more than 20%.
For defecate of the second class:
- neutralizing capacity – not less than 40% CaCO3;
- moisture content – not more than 30%.
Defecate with 20-30% moisture content is loose and contains 10-15% of organic matter, 0.2-0.7% of nitrogen, 0.2-0.9 P2O5 and 0.3-1.0% of K2O. When applied in CaO-equivalent amounts, defecate is superior to lime flour in terms of efficiency for all crops. Defecate is important not only on acidic soils, but also on chernozem soils in the areas of sugar beet cultivation.
Steelmaking slag – open-hearth, electric steelmaking, blast furnace slag.
According to the Russian regulatory requirements (ChMTU 11-37-69) they have the following requirements:
- neutralizing capacity must be not less than 80% CaCO3;
- humidity not more than 2%;
- particle size distribution: 70% of the mass must have a particle size of less than 0.25 mm, 90% less than 0.5 mm.
Most of the calcium is contained in the form of silicates, which are less soluble than CaCO3. For this reason, the effectiveness of steelmaking slag as a lime fertilizer depends on the fineness of the grinding.
In addition to calcium, magnesium and silicon, slags contain phosphorus, manganese and sulfur in their impurities. Therefore, the effectiveness of slags is often higher than equivalent doses of limestone and dolomite meal. The silicic acid contained is capable of chemically binding mobile aluminum, indirectly contributing to an increase in mobile forms of phosphorus in the soil.
Belite flour is a waste (sludge) in the production of aluminum. It contains 45-50% СаО, 25% mixture of Na2O and К2O, up to 30% SiO2, 3.4% Al2O3, impurities of phosphorus, sulfur and trace elements.
According to the particle size distribution 50% of flour should have particle size less than 0.15 mm, 90% – less than 1 mm. Belite flour is not inferior to other slags in efficiency.
Local lime fertilizers
Local lime fertilizers consist of loose (soft) carbonate rocks. In terms of their use in Russia, they are in third place. They do not require milling, exhibit faster action and efficiency than ground limestone.
Often local deposits of soft rocks are in areas of acidic soils, so their use to lime the surrounding areas agronomically and economically beneficial. The difference in the effectiveness of coarse and fine fractions of these fertilizers is expressed much weaker than the hard. According to the All-Russian Institute of Fertilizers and Agrochemistry, for 11 years all fractions smaller than 3 mm showed approximately the same effect on crop yields.
Limestone tuffs (spring lime)
Lime tuffs, or spring lime, consists of 70-98% CaCO3 with admixtures of organic matter, up to 25% clay and sand, 0.1% P2O5.
It is found in coastal floodplains, in places where springs emerge, and in the lowlands of the Non-Black Earth zone. In appearance they are loose, porous, easily crumbling mass of gray, sometimes rusty, brown or dark color.
Limestone tuffs with up to 30% moisture content and 85% of the mass is finer than 5 mm, according to the content of CaCO3 is subdivided into:
- first grade with more than 80% CaCO3;
- second grade with 70-80% СаСO3.
In terms of speed of action are superior to limestone.
Lake lime (gaja)
The lake lime, or gaja, is close to lime tuff in its chemical and granulometric composition. At humidity of 15-20% it contains up to 75-80% СаСО3 with admixtures of mineral and organic substances.
Deposits are more often found in dried up reservoirs, also collected by cleaning the bottom of existing reservoirs with subsequent drying. Lake lime has a fine-grained texture, easily scattered. It is a highly effective lime fertilizer.
Peat-tuffs are lowland peats containing from 10-20% to 50% CaCO3. They are a valuable lime-organic fertilizer. Effective on soils poor in organic matter and in need of liming.
The disadvantage of this type of lime fertilizer is the low profitability of their application, so it is advisable to use them at a small distance from the fields.
Marl contains 25-75% CaCO3, more than 1% MgCO3, and 20-40% sand and clay admixtures. Deposits occur as loose and dense masses. The action is slow.
Dense marl for the winter is advisable to remove to the fields, placing in small piles, which under the influence of changing temperatures and humidity in the spring scatter into small particles. After embedding in the soil in terms of efficiency, they are not inferior to lime meal. More often used on light soils.
Chalk contains 90-100% CaCO3 (up to 55% in terms of CaO) with an admixture of up to 0.6% MgO. The effect is superior to limestone, especially in the first years after application, in finely ground form is a good lime fertilizer.
Dolomite natural flour
Dolomite natural flour at moisture content up to 12% consists of 80% or more of calcium and magnesium carbonates in terms of CaCO3 with impurities.
According to its size distribution is a mass, 50-70% of which – particles smaller than 0.25 mm, up to 85% – less than 5 mm. It is a valuable lime fertilizer, and due to the magnesium it contains, it may be more effective than limestone meal on soils with light granulometric composition. Works slower than lime tuff.
Yagodin B.A., Zhukov Y.P., Kobzarenko V.I. Agrochemistry / Edited by B.A. Yagodin. – Moscow: 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 and Research Institute named after D.N. Pryanishnikov, 2017. – 854 с.