Calcium is a common chemical element found in nature. It can be obtained through limestone, chalk, and marble mining as well as the manufacturing of fertilizers that use calcium for active ingredients to stimulate plant growth rates
The purpose behind liming soil with this nutrient? To provide an alkaline pH level that will help plants become healthier by providing nutrients more efficiently than they would without aid from minerals like magnesium or potassium within the soil.
Calcium in nature
The general knowledge is that calcium is essential for healthy bones and teeth. It can be found in many compounds we are familiar with, both natural and synthetic. Chalk to lime caves or ancient fossils that have lain silent beneath the earth’s surface since they were first formed millions of years ago – all contain calcium! Gypsum stones on breakaway cliffs along highways represent one more example of how nature provides us with minerals necessary to our daily lives as humans living on this planet
With the invention of calcium in the early 19th century, it wasn’t used much at first. But now this metal is fifth on our list for mined resources and its importance increases every year. Many calcium compounds are widely used in industry. But calcium ions themselves play a more important role than their mere presence as an additive component of the mixture. It’s calcium that regulates the life processes of plants and animals; calcium plays a key role in calcium metabolism. Calcium has numerous important physiological functions. In fact, the role of calcium is so great that it can easily be categorized as a macronutrient.
There are few minerals in nature more abundant than calcium. Calcium accounts for 3% of Earth’s crust. Pure calcium is almost never found in nature but is a part of various compounds. For example, gypsum, fluorite, or limestone. The element mostly enters natural waters by leaching from silicates of different rock formations and sedimentary rocks, as well as with sewage from industrial and agricultural facilities.
A large amount of the element in water is one of the signs of water hardness. In water, it occurs in the form of salts of strong and weak acids: carbonates and hydrocarbonates (CaCO3), sulfates and sulfites (CaSO4, CaSO3) fluorides (CaF2), phosphates (Ca5(PO4)3), and others.
Calcium mobility and uptake by plants
Calcium uptake by plants is a passive process and doesn’t require any additional energy input. The mobility of the nutrient in plants occurs mainly in the xylem along with water, so its absorption is directly related to the transpiration rate of plants.
High humidity, cold and low transpiration rates can lead to calcium deficiency. Salinity can also cause deficiency by reducing water uptake by the plants.
Since the mobility of the nutrient in plants is limited, shortage of the macronutrient occurs first on young leaves (they die off) and in fruits (bud rot, bud drop, and necrosis) because transpiration is low. Therefore, feeding plants with calcium is necessary for their stable and prolonged growth.
Role of calcium in plants
The impact of calcium on the quality and volume of the crop is most often associated with disorders during fruit ripening and storage. Meanwhile, the role of the element in plant nutrition is much broader and most often underestimated. As a rule, the application of fertilizers occurs only in a situation of acute deficiency, when there is already a decrease in plant productivity and fruit quality. This is an unacceptable practice since its role in managing various plant processes is much larger.
Calcium is involved in many metabolic processes inside the plant. It’s essential for the formation of proper cell wall structure, as well as for cell division. It affects the metabolism of carbohydrates and proteins. The need for this nutrient is evident in the earliest periods of growth. Lack of calcium inhibits the processing and assimilation of stored nutrients (starch, proteins), which are used by seedlings, young leaves, and growing shoots. Approximately 90% of the nutrient is found in the cell walls, where it serves as a binding factor.
Calcium controls water balance, binds soil acids, provides normal conditions for the development of the plant root system, improves the solubility of many compounds in the soil. It contributes to the absorption of important nutrition elements by plants, influences the availability of a number of macro- and microelements to plants. Increasing the amount of calcium in the soil increases the inflow of ammonium and molybdenum ions into the plant, but the mobility of manganese, zinc, boron decreases. Lack of calcium cations in the soil leads to increased acidity of the soil solution (unless the soil is saline and contains excessive sodium).
Calcium deficiency in plants
Lack of calcium in the soil leads to deformation of plant cells, poor formation of covering tissues, abundant development of intercellular tissues that are poorly filled with lignin. With a lack of this nutrient, root growth slows down, and roots become lysed and rotten. Decomposed roots attract soil phytopathogens and saprophytes, being a favorable substrate for them.
Calcium enters plants during the entire period of active growth. Its penetration into plants increases with the presence of nitrate-nitrogen and decreases with the presence of ammonia nitrogen. In the case of a high concentration of calcium in the soil, hydrogen ions and other cations interfere with the nutrient uptake. It gradually passes from the soil to plants, and the soil is depleted. Calcium has rather low mobility in soil and plant tissues, where it’s mobilized almost exclusively by transpiration flux. It’s absorbed by the tips of the roots, and after entering the plant, it moves to the parts most actively involved in evaporation, namely the mature leaves.
Because of this limited mobility, the nutrient isn’t redistributed in the plant, so it can’t move from older to younger leaves as nitrogen does. Fruits and young leaves evaporate less or no water, and symptoms of deficiency appear on them first:
- The growth of young leaves is retarded;
- Small irregularly shaped leaves appear;
- The appearance of chlorotic spots;
- The tips of young leaves turn white;
- The edges of leaves curl downward, turn yellow and die off prematurely;
- The middle veins of leaves break;
- In case of severe deficiency, the plant top and flower stems die off, the stems grow weak;
- Brownish coloration or brown necrotic spots may appear on the edges of chlorotic leaves.
Calcium excess
Calcium toxicity is much more harmful than its deficiency: it binds iron compounds and makes them unavailable to the plant, leading to impaired absorption of nitrogen, potassium, and boron, causing mesic leaf chlorosis and the appearance of light shapeless spots of dying leaf tissue.
An overabundance of the nutrient can be a consequence of watering with very hard water. So it’s better to always know in advance the hardness of the water you are going to use, for example by having it tested for calcium.
If the soil experiences calcium toxicity, the best thing to do is to change the substrate, at least partially. In hydroponics, excess of the nutrient, like any other excess, is solved by changing the solution. Just make sure that the problem is not in the hardness of the water you use because otherwise, the problem will occur again.
Calcium fertilizers
Lime fertilizers are the main source of the nutrient for plants. These fertilizers can be classified into the following groups:
- Hard lime rocks;
- Soft lime rocks;
- Industrial wastes with a high lime content.
Hard lime rocks are subdivided according to the content of CaO and MgO into:
- lime fertilizers (55-56% CaO and up to 0.9% MgO);
- dolomitized lime fertilizers (42-55% СаО and up to 9% MgO);
- dolomites (32-30 % СаО and 18-20 % MgO).
Common calcium-containing fertilizers
Agricultural limestone
This is the most common lime fertilizer. It contains 75-100% Ca and Mg oxides in terms of CaCO3.
Dolomitized lime compounds
These contain 79-100% of the active substance in terms of CaCO3. Recommended in crop rotations with potatoes, legumes, flax, root crops, as well as strongly podzol soil types.
Mergel
Contains up to 25-15 % СаСО3 and impurities in the form of clay with sand up to 20-40 %. It works slowly. Recommended for use on light soils.
Chalk
Contains 90-100% СаСО3. Acts faster than agricultural lime. A valuable, finely ground lime fertilizer.
Burnt lime (CaO)
The content of CaCO3 is more than 70 %. Characterized as a strong and fast-acting material for liming.
Quicklime (Ca(OH)2)
The content of CaCO3 is 35 % and more. It’s also a strong and fast-acting lime fertilizer.
Dolomite meal
CaCO3 and MgCO3 content is about 100 %. Acts slower than lime tuff. Usually used where magnesium is required.
Calcareous tuffs
The content of CaCO3 is 15-96%, impurities – up to 25% of clay and sand, 0.1% P2O5. Acts faster than agricultural lime.
Defecation mud (defecate)
This one consists of CaCO3 and Ca(OH)2. The content of lime on CaO is up to 40%. It also contains nitrogen – 0.5% and P2O5 – 1-2%. This is a waste product of sugar beet factories. It’s recommended for use not only to reduce the acidity of soils but also in areas of beet-sowing on chernozem soils.
Shale Cyclone Ash
Dry dust-like material. The content of the active ingredient is about 60-70%. Relates to industrial wastes category.
Dust from kilns and cement plants
The content of CaCO3 must exceed 60%. Most commonly used on farms located in the vicinity of cement plants.
Organic fertilizers
The content of Ca in terms of CaCO3 is 0.32-0.40 %.
Phosphate meal
The content of calcium is 22% of CaCO3.
Importance of fertilizer application
Lime fertilizers are not only used to provide calcium to the soil and plants. The main purpose of their use is to lime the soil. This is a method of chemical reclamation. It’s aimed at neutralizing excessive soil acidity, improving its agrophysical, agrochemical, and biological properties, supplying plants with magnesium and calcium, mobilization and immobilization of macroelements and microelements, and creating optimal water-physical, physical, and air conditions for cultivated plants.
Effectiveness of soil liming
Along with meeting the needs of plants in calcium as a mineral nutrient, liming leads to multiple positive changes in the soil.
Calcium helps to coagulate soil colloids and prevent their leaching. This leads to easier tillage of the soil, improving its aeration.
As a result of liming:
- Sandy humus soils increase their water-absorbing capacity;
- Soil aggregates and clods are formed on heavy clayey soils, improving water permeability.
Impact of liming on the cationic composition of soil
In particular, the result of liming is that organic acids get neutralized and hydrogen ions are displaced from the absorbing complex. This leads to the elimination of exchange acidity and reduction of hydrolytic acidity of the soil. At the same time, there is an improvement of the cationic composition of the soil absorbing complex that occurs due to the replacement of hydrogen and aluminum ions by calcium and magnesium cations. This increases the degree of saturation of soils with bases and increases the absorption capacity.
Influence of liming on the nitrogen supply to plants
After liming, the positive agrochemical properties of the soil and its structure can be maintained for several years. It helps to create favorable conditions for strengthening useful microbiological processes of nutrient mobilization. The activity of ammonificators, nitrifiers, nitrogen-fixing bacteria freely living in the soil is enhanced.
Liming contributes to strengthening the reproduction of nodule bacteria and improving the supply of nitrogen to the host plant. It has been found that bacterial fertilizers lose their effectiveness in acidic soils.
Influence of liming on the supply of ash elements to plants
Liming contributes to the supply of ash elements to plants as the activity of bacteria increases, decomposing organic phosphorus compounds of soil and facilitating the transition of iron phosphate and aluminum into available plants phosphorus calcium salts. Liming of acidic soils enhances microbiological and biochemical processes, which in turn increases the number of nitrates as well as assimilable forms of phosphorus and potassium.
Effect of liming on the form and availability of macronutrients and trace elements
Liming increases the amount of calcium, and, when using dolomite meal, magnesium. At the same time, toxic forms of manganese and aluminum become insoluble and pass into the precipitated form. Availability of such elements as iron, copper, zinc, manganese decreases. Nitrogen, sulfur, potassium, calcium, magnesium, phosphorus, and molybdenum become more available.
Effect of liming on the action of physiologically acidic fertilizers
Liming increases the effectiveness of physiologically acidic mineral fertilizers, especially ammonium and potassium fertilizers.
The positive effect of physiologically acid fertilizers without the addition of lime fades, and over time can turn negative. So yields from fertilized plots are even less than from unfertilized ones. The combination of lime and fertilizer increases their effectiveness by 25-50%.
Lime activates enzymatic processes in the soil, which is indirectly judged on its fertility.
Conclusion
Along with soil humus, calcium is directly and indirectly involved in the formation of fertility, as it’s not only a supplier of nutrients. Exchangeable calcium is retained by the soil stronger than other cations (Mg and K) and occupies 75-85% of the total cation exchange capacity in non-acidic soils. This means that this nutrient impacts the pH balance of the soil, as well as multiple processes occurring in it, manifested through the physical, chemical, and biological effects.
Without sufficient saturation soil with calcium, the soil profile develops firm particles, which subsequently stick together, forming a cohesive, dense structure that is poorly permeable to water and air.
By stabilizing the soil with calcium-containing fertilizers, you reduce the risk of over-compaction of the soil.
