The content of total phosphorus (P 2 O 5 ) in China's soil is in the range of 0.05% to 0.3%, and the distribution law is gradually increasing from south to north. The form of phosphorus in the soil is diverse and continuously transformed with each other, which has an effect on the fertilizer efficiency and phosphorus supply capacity of the phosphate fertilizer. First, the form of phosphorus in the soil Soil phosphorus is divided into organic phosphorus and inorganic phosphorus according to its chemical structure, accounting for 10%-30% and 70%-90% of total phosphorus content respectively; according to its solubility, it can be divided into water-soluble phosphorus, strontium-soluble phosphorus, and difficult. Soluble phosphorus. Figure 1 shows the dynamic changes in soil phosphorus form. Figure 1 Dynamic changes of phosphorus in soil Water-soluble phosphorus: such as phosphoric acid-calcium [Ca(H 2 PO 4 ) 2 ], potassium dihydrogen phosphate (KH 2 PO 4 ) and the like are soluble in water, and are easily absorbed and utilized by crops, but the amount is small and extremely unstable. Citrate soluble phosphorus: such as dicalcium phosphate (Ca 2 HPO 4), dicalcium phosphate, magnesium (Mg 2 HPO 4) was dissolved in 2% citric acid and the like or ammonium citrate solution, insoluble in water. They are mostly distributed in near-neutral soils and are easily dissolved by crop root secretions and converted into water-soluble phosphates. Insoluble phosphorus: The fluoroapatite [Ca 10 (PO 4) 6 · F], chlorine apatite [Ca (PO 4) · Cl 2], aluminum phosphate salt [AlPO 4 · Al (OH) 3 Inorganic phosphorus such as iron phosphate (FePO 4 ), and organic phosphorus such as inositol phosphate, inositol phosphate, phosphoinositide, and phospholipid. They are only soluble in strong acids and are difficult to absorb. Soil water-soluble phosphorus and strontium-soluble phosphorus, called soil availability phosphorus, also known as soil available phosphorus, accounts for about 1% of total phosphorus in soil. The higher the degree of soil ripening, the greater the amount of farmyard manure and phosphate fertilizer, and the more effective soil phosphorus content. Second, the conversion of phosphorus in the soil Under certain conditions, soil availability phosphorus can be converted into poorly soluble phosphorus, also known as phosphorus fixation, and its effectiveness is reduced; poorly soluble phosphorus can also be converted into effective phosphorus, called phosphorus release, and its effectiveness is improved. (I) Phosphorus fixation Phosphorus is fixed in alkaline soil, acid soil and neutral soil. 1. Fixation of phosphorus in alkaline soil Soil available phosphorus easily forms octacalcium phosphate [Ca 8 H 2 (PO 4 ) 6 ·5H 2 O] in calcareous alkaline soil, and crops are not easily absorbed. 2. Fixation of phosphorus in acid soil The water-soluble phosphorus is mainly fixed by iron and aluminum in the soil to form insoluble iron phosphate aluminum phosphate, which accounts for more than 70% of the inorganic phosphorus content. A considerable part of it is encapsulated by iron oxide film. "Closed-state phosphorus" with lower solubility. 3. Fixation of phosphorus in neutral soil Water-soluble phosphorus combines with calcium and magnesium ions in soil to form dicalcium phosphate and dimagnesium phosphate. It takes a long time for the dicalcium phosphate to gradually change to a slightly less soluble octacalcium phosphate and anhydrous dicalcium phosphate. In addition, part of the soil's available phosphorus is temporarily fixed by soil microorganisms. Soil available phosphorus is relatively stable in near-neutral calcareous soils. It is mainly fixed as dicalcium phosphate, adsorbed on the surface of soil particles, with high fineness, and is easily converted into monocalcium phosphate by acidic substances in the soil. (II) Release of phosphorus Soil organic matter, water content and pH have a great influence on the release of phosphorus. 1. Influence of soil organic matter High organic matter content can provide sufficient "food" for microorganisms, promote the proliferation of phosphorus bacteria, and strengthen the decomposition of poorly soluble phosphorus in soil; carbon dioxide and organic acids produced during the decomposition of organic matter are beneficial to the release of phosphorus. The organic acid can also form a complex [Fe(OH) 2 · organic acid] with active iron (or aluminum) in the soil to reduce the fixation of phosphorus. 2, the impact of soil moisture Soil moisture is suitable for the diffusion, hydrolysis of phosphate, easy to be absorbed by crops. In the flooded state, the acidic soil is weakened and the reducing property is enhanced. Some of the "closed-storing iron phosphate" is reduced to "non-closed storage iron phosphate", and the effectiveness of phosphorus is increased. In the opposite period, the soil available phosphorus is decreased. . 3, the impact of soil acidity Near neutral soil not only effective phosphorus is relatively stable, but also a good environment for soil microbial growth. Therefore, the acidic soil is added with an appropriate amount of lime, and the alkaline soil is added with an acidic substance such as phosphogypsum , which can reduce the fixation of the available phosphorus in the soil and facilitate the release of the poorly soluble phosphorus. Considering fertilization, although the moderate fixation of phosphate fertilizer reduces the fertilizer efficiency in the current season, it also has a positive side, namely, reducing the loss of phosphorus leaching and maintaining its strong aftereffect. We should prevent excessive fixation of phosphorus and affect the normal growth of crops. Therefore, increasing the application of farmyard manure and improving the physical and chemical properties of soil is one of the effective ways to improve the efficiency of phosphate fertilizer. However, it is not possible to blindly and heavily apply phosphate fertilizer because the soil has a large buffering effect on phosphorus. This is because: on the one hand, too much phosphorus in the soil will reduce the effectiveness of some trace elements such as zinc , on the other hand, excessive accumulation of phosphorus in the soil will also be lost into the water pollution environment. Some foreign studies have suggested that the effective phosphorus in the soil (phosphorus measured by the Olsen method) is little lost within 60 mg/kg. The loss of forest in the soil beyond this turning point increases sharply with the increase of soil available phosphorus. It is estimated that about 3 million to 4 million tons of phosphorus (P 2 O 5 ) are transferred from the soil to the water every year. Third, the relationship between soil phosphorus and phosphorus application The insoluble phosphorus in the soil can only be used as the “phosphorus reservoir†of the soil, that is, the potential fertility, and the crop cannot be absorbed. Soil available phosphorus accounts for only about 1% of total phosphorus and can be absorbed by crops. Roughly calculated, the soil available for 667 square meters of ploughed soil can provide about 0.8-0.4 kg of available phosphorus (P 2 O 5 ). The higher the soil available phosphorus, the greater the phosphorus supply capacity for crops. Under the same conditions of other production conditions, the soil available phosphorus content is negatively correlated with the fertilizer efficiency of the phosphate fertilizer: the higher the soil available phosphorus content, the lower the fertilizer application efficiency. When 667 square meters of grain is produced from 350 to 400 kilograms, it is necessary to absorb phosphate fertilizer (P 2 O 5 ) of about 4.2 to 4.8 kilograms. Most of this production level is 5 to 7 kg of phosphate fertilizer (P 2 O 5 ). The utilization rate of phosphate fertilizer in the season is about 15%, and the phosphate fertilizer (P 2 O 5 ) absorbed by crops is about 0.9 kg. At this time, about 20% of all the phosphorus absorbed by the crop comes from fertilization, and 80% comes from the soil. Therefore, the application of phosphate fertilizer is of great significance for high yield and maintaining soil phosphorus supply capacity. HbA1C Analyzer,POCT HbA1C Analyser,HbA1C POCT Analyzer,Automated HbA1C Analyzer ZSL MED , https://www.zslmed.com