1. Calcium content and distribution in plants
Generally, the calcium content (Ca) of plants accounts for 0.1% to 5% of the dry weight of plants, and its content varies depending on the plant species and organs. According to the amount of calcium in plants, they are divided into two categories, namely calcium-loving plants and calcium-hating plants.
Calcium-loving plants are generally dicotyledonous plants, such as legumes, cotton, alfalfa, beets, cabbage, tomatoes, etc. The plants have a high calcium content and require a lot of calcium. The aboveground calcium content is 1% to 5%. Calcium-loving plants are mainly distributed in calcareous soil areas with high calcium carbonate (CaCO3) content, but are prone to iron and manganese deficiency symptoms.
Calcium-hating plants are generally monocotyledonous plants. The plant calcium content is low and the calcium requirement is also low. The aboveground calcium content is 0.25% to 0.5%. Calcium-hating plants grow well on acidic soils with less calcium, can tolerate high concentrations of Al3+, and are not prone to iron and manganese deficiency symptoms.
2. The role of calcium
1. Calcium is an important component of the cell wall
Most of the calcium in plants is a pectin structural component of the cell wall. It forms calcium pectate with pectin acid and is fixed between two adjacent cell walls, that is, in the middle gelatin layer, to maintain the structure and function of the cell wall. When calcium is deficient, the adhesion between calcium and pectin in the middle gelatin layer is affected, and plant tissues are vulnerable to pathogens. Therefore, calcium can enhance the disease resistance of plants, making crops resistant to storage, transportation and not easy to rot.
2. Calcium can stabilize the cell membrane
Calcium acts as a link between phosphate and protein carboxyl in the cell membrane. It is reported that calcium can increase the activity of superoxide dismutase and reduce the content of membrane lipid malondialdehyde, thereby protecting the integrity of the cell membrane structure.
3. Calcium acts as a second messenger
Calcium can bind to calmodulin (CaM) in plant cells to regulate enzyme activity and act as a second messenger for hormone and environmental signal transduction. At present, it is believed that CaM is closely related to cell division and differentiation, cytoskeleton and cell movement, photosynthesis, germination of spores, seeds and pollen, response to hormones, nuclear enzyme system and gene expression.
4. Calcium has a physiological regulatory effect
Calcium can neutralize organic acids generated by plant metabolism, form insoluble organic calcium such as calcium oxalate, calcium citrate and calcium malate, adjust pH value and stabilize the intracellular environment. Calcium ions can reduce the dispersion of protoplasm, adjust the colloidal state of protoplasm, and make the cell water filling, viscosity, elasticity and permeability suitable for crop growth.
5. Calcium and plant cold resistance
Low temperature stress causes a large number of free radicals to be produced in plants, causing damage to the membrane system and causing low temperature damage. Calcium can slow down the reduction rate of superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) in plants under low temperature stress. These three enzymes are important protective enzymes in plants, play an important role in scavenging free radicals, and are closely related to plant stress resistance. Therefore, calcium can effectively improve the cold resistance of plants.
6. Calcium and drought resistance of plants
Calcium can regulate the activity of certain enzymes, transmit and induce the expression of drought signals, and improve the water retention capacity of plants.
7. Calcium and salt tolerance of plants
Calcium can regulate the ion balance in plant cells and reduce the absorption of sodium ions. Recent studies have shown that calcium can promote the selective absorption, transportation and distribution of ions.
3. Calcium deficiency
Calcium has poor mobility in crops and mainly moves upward through the transpiration of crop leaves. Once there is insufficient calcium in the soil, it is easy to show symptoms of deficiency. I have talked about the role of calcium on crops above. When calcium is deficient, the following symptoms will be mainly manifested.
1. Cause the occurrence of diseases
After crops are calcium deficient, the most common is cracked fruit, such as grapes, pomegranates, tomatoes, etc., in the middle and late stages of growth, the peels of fruits crack. At the same time, it weakens the resistance of crops to diseases, leading to the occurrence of various diseases. Common bitter pit disease on apples, leaf scorch on vegetables, and navel rot on tomatoes are all diseases caused by calcium deficiency.
2. Slow growth of crops
Calcium has poor mobility in crops, so it is easy to show symptoms of deficiency in new leaves. Once new leaves lack calcium, they will grow slowly, turn yellow and curl, and in severe cases, dry and fall off. Since crop growth requires the growth hormone secreted by new leaves to regulate the absorption of nutrients by the roots, when new leaves grow abnormally, it affects the absorption of nutrients by the roots, thus causing the problem of slow growth of crops.
3. Decrease in crop yield and quality
Calcium deficiency affects the photosynthesis of crops and inhibits the ability of roots to absorb nutrients, resulting in weak growth and premature aging of crops. Moreover, calcium is an important component of fruit epidermal cells. Calcium deficiency can cause thin stems and weak seeds of crops. For fruit trees, it causes the tree to weaken, the conversion rate of various nutrients in the fruit slows down, the fruit is prone to cracking and falling, and the commercial rate is greatly reduced.
4. Excessive calcium
The soil is prone to become neutral or alkaline, causing a lack of trace elements (iron, manganese, zinc), the color of the leaf flesh becomes lighter, and red spots or stripes appear on the leaf tips
- Root tip dieback: Excessive calcium will cause the soil acidity to decrease, hindering the root system from absorbing nutrients. At the same time, high concentrations of calcium ions will also cause poisoning, leading to necrosis at the root tip.
- Inhibit microbial activity: Excessive calcium ions will inhibit the activity of microorganisms in the soil, affecting the nutrient absorption and growth and development of the root system.
- Destroy soil structure: When calcium ions combine with other elements in the soil, they will form salts that are difficult to decompose, thereby destroying the soil structure, making it dense, and affecting the supply of water and oxygen to plants.
- Promote leaf fall and withering: Excessive calcium ions may cause leaves to lose green pigment, thereby promoting yellowing, withering and leaf fall of plant leaves.
5. Reasons why it is difficult to supplement calcium in crops
1. Calcium is an inert element. In nature, calcium ions easily combine with various anions to produce precipitates that are difficult to dissolve in water, which are then fixed and not absorbed by crops; in plants, the parts that need calcium are mostly located at the top of the crop’s growth (such as leaf buds, tender shoots, etc.) and fruits. After calcium is absorbed by the roots, it is easy to combine with organic acids during the upward transportation process through transpiration, resulting in the formation of organic acid calcium that is difficult to transport and cannot reach the parts that really need calcium.
2. Calcium and various elements will have antagonism, such as potassium, iron, zinc, boron, etc., and calcium is the most inert element. That is: when multiple elements exist at the same time, plants will give priority to absorbing other elements instead of calcium. For example, during the fruit expansion period, when potassium is used in large quantities, fruit trees will only absorb potassium and refuse calcium. If crops are likened to picky children, then calcium is undoubtedly the most unpopular food.
6. When crops need calcium supplementation, it is best to supplement boron at the same time
When plants are calcium deficient, they first show symptoms in new roots, apical buds, fruits and other parts that are growing vigorously and tender, with symptoms ranging from wilting to necrosis.
Calcium deficiency can increase the permeability of plant cell membranes and can also cause the cross-linking and disintegration of cell walls, seriously affecting the appearance and quality of agricultural products. Generally, fruits and storage organs have very poor calcium supply, and fruits and vegetables are often judged to be calcium deficient by the deformation of storage tissues.
After calcium is absorbed into the roots, it is basically transported upward through the xylem. Calcium is difficult to transport in the phloem, so it is difficult to transfer downward. Therefore, all organs supplied by phloem sap, such as seeds and fruits, have low calcium content. Therefore, some people say that “regardless of whether there is calcium deficiency in the soil, plant fruits must be calcium deficient.” In addition, calcium is easy to form insoluble calcium salt precipitation and fix in the plant body, so it cannot be moved and reused.
7. What should be paid attention to when applying calcium fertilizer?
1. Choose appropriate calcium fertilizer and use reasonable application methods
Traditional calcium fertilizers applied to the soil mainly include lime, calcium nitrate, calcium chloride, calcium carbonate, superphosphate and calcium magnesium phosphate fertilizer. Calcium fertilizers with high solubility such as calcium nitrate and calcium chloride can be dissolved and sprayed, or watered immediately after applying calcium fertilizer to the soil to improve fertilizer utilization. Superphosphate should be applied after composting with organic fertilizer. Calcium chloride can easily cause soil salinization and is rarely used in production. Large-scale application of lime can easily cause soil pH to rise, affecting the soil microbial environment.
At present, it is recommended to apply liquid calcium fertilizer on facility vegetables and fruit trees. Liquid calcium fertilizer mostly uses chelating agents to increase the stability of calcium, such as amino acid calcium, humic acid calcium and sugar alcohol chelated calcium. The most advanced and efficient technology is sugar alcohol chelation technology. This type of sugar alcohol chelated calcium can not only improve the absorption rate of calcium, but also absorb it through the leaves and fruit surfaces, and can be used after bagging.
2. Pay attention to the calcium supplementation period
The first peak period: the spring shoot budding period, mainly to meet the root growth.
The second peak period (May-August): the young fruit expansion period, mainly used to promote the formation of fruit cell walls.
The third peak period (September-November): the autumn shoot period, mainly for root growth, fruit expansion, and shoot extraction.
The peak of calcium demand for general crops is in the young fruit period. During this period, attention should be paid to direct calcium supplementation of fruits in small amounts and multiple times.
3. When supplementing calcium, pay attention to supplementing boron at the same time
In order to increase the application effect of liquid calcium fertilizer, elements such as boron and zinc are added to liquid calcium fertilizer. Boron fertilizer plays a key role in the growth and development period of fruits. It can promote flower bud differentiation and increase fruit setting rate and fruiting rate. Boron has a more significant effect, which is its strong transportation capacity. Boron can make carbohydrates in plants work, which is equivalent to the commander-in-chief. It can quickly deliver the elements and nutrients needed by various organs, which is conducive to leaf absorption, so that crops can grow normally.
The calcium-boron liquid fertilizer provided by Wellyou Tech is based on the principles of plant nutrition physiology, with multiple nutrients such as amino acids, fulvic acid, chitosan, organic matter, protein, vitamins, etc., organically chelating large, medium and trace elements such as nitrogen, potassium, calcium, and boron required by plants. It adopts the latest bioengineering technology and is developed by scientific formula.
It has the following characteristics:
- Strong activity, high regulatory power, can be absorbed quickly without hoarding, and the crop nutrients are efficiently absorbed to ensure the healthy growth of crops;
- Rapidly supplement calcium elements, effectively prevent nutrient deficiency, increase production and quality;
- Strengthen disease prevention and resistance functions, and have obvious effects on the recovery of crops and weak plants after disasters;
- Improve crop quality, prevent fruit cracking, deformity, etc., with significant effects.
