What is the residue?
The calcium salt of the title is water-soluble phosphate fertilizer, which belongs to the low-concentration phosphate fertilizer variety. Its composition is complex, not a single water-soluble phosphate, but a mixture of one type. The main component is calcium dihydrogen phosphate, which is soluble in water and easily absorbed by crops. It is a quick-acting phosphate fertilizer, but the effective phosphorus content is not high, and the P2O5 is 14% to 18%. In addition to water-soluble phosphorus, the calcium contains 40% to 50% of water-insoluble calcium sulfate (common name gypsum), and contains 2% to 4% of various water-insoluble sulfates such as magnesium sulfate and iron aluminum sulfate. It can be seen that the calcium salt, which is called water-soluble phosphate fertilizer, is mostly composed of medium-sized nutrients such as sulfur and calcium. These are water-insoluble components. When a large amount of calcium is applied to the soil surface, a small amount of water-soluble phosphorus dissolves in the irrigation or rain and migrates to the soil, and most of the water-insoluble gypsum becomes a residue and remains on the farmland surface. It is important to know that these residues are intermediate micronutrients necessary for crop growth. On the plots of vegetables, fruits, pineapples and various economic crops, with high yields in successive years, the crops have taken away a lot of micronutrients such as calcium and sulfur, but the fertilization in production now only emphasizes the supplement of nitrogen, phosphorus and potassium, which is often ignored. A balanced supplement of micronutrients. Calcium can take on the task of supplementing micronutrients. Unfortunately, many first-line producers do not realize it, so there is a misunderstanding in the use of calcium.
The nature and application of calcium
From the appearance and physical and chemical properties, calcium is a grayish white powder or granular form, often acidic due to a small amount of free acid, and slightly acid smell, corrosive to the packaging bag. The presence of free acid also makes the fertilizer easy to absorb moisture and agglomerate. Serious moisture absorption causes chemical changes in the fertilizer, which causes some water-soluble monocalcium phosphate to be converted into insoluble iron phosphate and aluminum phosphate, which reduces the content of available phosphorus. It is called the degeneration of superphosphate. This effect mainly occurs during the storage process before the application of the fertilizer. For this reason, it should be strictly protected from moisture during storage and transportation, and the storage time should not be too long.
The agrochemical properties of calcium from the performance of soil application: water-soluble calcium is very unstable in the soil, is easily affected by various conditions and is fixed, and becomes a water-soluble phosphate to reduce fertilizer efficiency. . This poor fixation can occur in both calcareous and acidic soils, which is the main reason for the low utilization of phosphate fertilizer (generally only 10% to 25%). This common feature of calcium and other phosphate fertilizers is exactly the opposite of the nature of nitrogen fertilizer. Therefore, it is decided that in the scientific fertilization of farmland, the application position of common calcium should be particularly particular. The principle is: to reduce the contact between fertilizer and soil, to avoid the fixation of water-soluble phosphate, and to apply the phosphate fertilizer to the soil layer with dense roots, and to increase the contact between calcium and roots, which is beneficial to absorption. Calcium fertilization should be applied in a relatively concentrated manner (such as ditch application and acupoint application); the base fertilizer and the seed fertilizer should be applied in layers; the top dressing should not be applied to the surface and must be applied to the corresponding depth. Agricultural production experience has proved that the concentrated application of superphosphate is the most cost-effective method of fertilization. If the utilization rate of application is only 13%, the semen root is 38%, and the root can reach 48%. Therefore, centralized application of phosphate fertilizer can significantly improve the utilization rate of phosphate fertilizer resources. In addition, the use of calcium into granules can reduce the contact surface of phosphate fertilizer with the soil, thereby reducing the adsorption and fixation of available phosphorus by the soil. The particle size of granular phosphate fertilizer should not be too large, generally 2-3 mm is preferred.
From the nutritional characteristics of crop phosphorus, the application period of calcium phosphate can be used as base fertilizer, seed fertilizer and top dressing.
Phosphate fertilizer can improve the nutrition of crop seedlings. The top dressing can avoid the fixation of soil application, which is beneficial to the rapid absorption of crops and can save fertilizer.
Today, for the calcium phosphate of China's unit phosphate fertilizer, there should be an overall evaluation: although it has low concentration, it has many nutrient-containing varieties and low prices, and the resources for producing calcium in China are rich, and the production and application of calcium can not only improve. The utilization efficiency of phosphorus nutrient resources will also develop and utilize valuable medium-weight element nutrients to reduce the piles of waste residue from the production of high-concentration phosphate fertilizer. Therefore, re-evaluation of calcium is of great significance to China's agricultural development.
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