Calcium concentration is more cost effective

Recently, some farmers' letters were reflected in vegetables, green corn, pineapples and other economic crop plots. It was found that there were obvious gray-white powder residue on the soil surface of the plant roots. It was originally a residue of phosphate fertilizer called “Pu-calcium”. . Why are there so many residues left? How to apply calcium can not leave a lot of residue and other problems. This magazine invites experts to give answers.

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 not a single water-soluble phosphate, but a mixture of one type. The main component, calcium dihydrogen phosphate, is soluble in water and easily absorbed by crops. It is a quick-acting phosphate fertilizer. However, the effective phosphorus content is not high, and the P2O5 is 14% to 18%. In addition to the water-soluble phosphorus, the calcium contains 40% to 50% of water-insoluble calcium sulfate (common name gypsum), and also contains 2% to 4%. Various water-insoluble sulfates such as magnesium sulfate and iron aluminum sulfate. It can be seen that the crown is called water-soluble phosphate fertilizer. Most of its components are medium-sized nutrients such as sulfur and calcium, which are mostly 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 materials such as water-insoluble gypsum become residues and remain in the farmland surface.

Therefore, these residues are some of the micronutrient elements necessary for the growth of some crops. It is unreasonable to cause pollution in the field of farmland by weathering and raining for a long time. However, in the fields of vegetables, fruits, pineapples and various economic crops, with high yields in successive years, the crops have taken away a lot of calcium, sulfur and other micronutrients. Elements, and people only emphasize the supplement of nitrogen, phosphorus and potassium in the fertilization in production, and often ignore the balance supplement of medium and micro nutrient elements. In fact, calcium is a good source of fertilizer for this task.

Comprehensive understanding of the nature, master the principle of scientific application From the appearance and physical and chemical properties, calcium is a gray-white powder or granular form, often acidic due to a small amount of free acid, and slightly acid smell, corrosive to the packaging. 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. Since the monocalcium phosphate in the fertilizer is easily fixed by the soil, the behavior of the calcium in the soil has the characteristics of being easily fixed and having little mobility and being difficult to migrate. 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, and to prevent the water-soluble phosphate from being fixed. It is necessary to apply the phosphate fertilizer to the soil layer with dense roots, which is beneficial to the absorption of calcium and root. This suggests that the application of calcium and fertilization should be relatively concentrated (such as ditch application and acupoint application); the base fertilizer and the seed fertilizer should be applied in layers; the technical principle that the top dressing should not be applied to the surface and the corresponding depth must be applied. Agricultural production experience has proved that the concentrated application of superphosphate is the most cost-effective method of fertilization. If the utilization rate is only 13%, the sapling 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. In fact, the preparation of granules has the same meaning as the concentrated application. The particle size of the granular phosphate fertilizer should not be too large, and it is generally 2 to 3 mm. Especially for soils with high phosphorus fixation capacity, the effect of granular phosphate fertilizer is more obvious. At the same time, the granules are also convenient for mechanized fertilization.

From the characteristics of phosphorus nutrition of crops, the application period of calcium phosphate should be used as base fertilizer, seed fertilizer and topdressing. The seedling stage is the critical period of phosphorus nutrition, and the use of appropriate amount of calcium as a seed fertilizer can play the role of four or two. It is an economical and effective method of application. However, it should be noted that the fertilization position is 3 to 5 cm below the seed.

Calcium as a root top dressing is also a cost-effective application method, which can avoid the fixation of soil application and is beneficial to the rapid absorption of crop flowering results. At this time, the ability of roots to absorb nutrients generally declines. Spraying phosphate fertilizer can increase the 1000-grain weight of rice and wheat, the weight of cotton and the fruit set rate of fruit trees. However, since the calcium contains a large amount of non-water-soluble complex components, the mother liquor should be prepared in advance, and after a certain period of time to be clarified, the supernatant liquid is taken for spraying, and the sediment of the mother liquid bottom layer is used as a base fertilizer or mixed into a circle fertilizer. Avoid waste and pollution.

In short, we should change our mindset, re-evaluate calcium, and help farmers to use calcium to serve China's double-high agriculture.

(Senior Consultant of Sinofert, Professor of China Agricultural University Cao Yiping)
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