The main basic substances in alkaline soils are calcium, magnesium, sodium carbonates and bicarbonates, as well as exchangeable sodium adsorbed on alternate surfaces. Sodium carbonate and sodium bicarbonate are water-soluble, so the concentration of sodium ions in the soil solution is kept constant, in other words, the ability to affect the root system is also fixed. However, carbonates or bicarbonates such as calcium, magnesium, iron, etc. are all water-insoluble strong base weak acid salts, which are insoluble in water and are difficult to be directly absorbed by crops, but in the case of more acidic acids. At that time, for example, urea phosphate, carbonate and bicarbonate will release carbon dioxide and calcium, magnesium, iron, etc., lowering the soil pH and activating beneficial elements such as calcium, magnesium and iron. The released calcium ions can inhibit the absorption of sodium ions by plant roots. For example, Xie Taiyun and others believe that the use of urea urea fertilizer, the formation of a lower pH environment around the fertilization point, reducing ammonia volatilization; Li Yanting and other use of pH=1.0-2.0 acidic rhizosphere fertilizer around the root, the diffusion radius in the soil is 6cm, The effective distance to soil pH reduction is 2 cm. Within 28 days of fertilization, the soil pH was reduced by 0.9 units 2 cm from the fertilizer. Soil iron availability (DTPA leaching) increased by 5.9 mg/kg, significantly increasing the absorption of iron by peanuts. Zhang Li et al. studied the effects of urea phosphate on soil pH, plant growth and leaf physiological characteristics under alkaline stress conditions. The treatment with alkali-free stress reduced 2.69 units, plant height and leaf area. The whole plant dry matter increased by 23.55%, 21.03% and 33.84% compared with alkali stress treatment. Liu Jian et al. applied the drip irrigation of cotton under the urea film in the Shihezi area of Xinjiang. It showed that the urea phosphate can exert the controllable advantages of drip irrigation technology, improve the fertilizer utilization rate, promote the growth of cotton, improve the quality of cotton, and increase the yield of lint by 7.4%-10.8. %, fertilizer efficiency is better than other drip irrigation.
Domestic and foreign research
Create a urea phosphate high-efficiency fertilizer
Urea phosphate was first applied for patents by BASF in Germany in 1914. Subsequently, countries followed up the research and formed industrial production in the 1970s. They were mainly used as feed additives and nitrogen-reducing ability and high-efficiency compound fertilizer. Urea phosphate has many advantages, such as strong solid acid, high nutrient, good water solubility, ability to prevent precipitation of calcium and magnesium, high processing performance and low cost. It has become the preferred raw material for the development of alkaline soil high-efficiency fertilizer and development of calcium-containing magnesium fertilizer.
In foreign countries, in 1992, American Omers Investment Company applied for solid blended fertilizer. The product contained phosphorus and calcium. It was mainly composed of urea phosphate and calcium nitrate. The solid product was not precipitated by the acidity of urea phosphate. In 1996, Kemira applied for a patent for suspension fertilizer containing phosphate and calcium magnesium in China, mainly through acid regulation (pH=0.5-2.0) and grinding to form a high concentration of suspended fertilizer. In 2009-2010, the French company Frimers applied for a patent for instant water-soluble fertilizer products in many countries. The product is stable in the dry state, dissolves quickly, has no precipitation, and the acidic substance contains urea phosphate.
Domestically, in 2002, Zhang Xiaoyong of the Institute of Process Engineering of the Chinese Academy of Sciences applied for a patent for drip irrigation of acidic liquid fertilizer for Xinjiang soil. This solution solves the water solubility of monoammonium phosphate and solves the problem of drip irrigation clogging. In 2003, Liu Jian and others also applied for the patent of high-efficiency compound fertilizer using urea phosphate as raw material. The product is powdery and has strong acidity. Nubefeng Company has launched a water-soluble composting partner to solve the problem of fertilizer precipitation caused by hard water in Shanxi and Xinjiang, and blocking the drip irrigation pipeline. The main component of this product is urea phosphate. The method is to use the water-soluble fertilizer urea urea in a ratio of 1:5-10. The effect is remarkable. Yunnan Evergreen Company has launched “Liaolingling”, whose core component is also urea phosphate, which is mainly promoted in Xinjiang and other regions. Phosphoric acid urea is used alone or as a raw material for water-soluble fertilizer, which is used as a standard, and the pH is diluted between 1:6.5 times and the pH is between 6.5 and 7.0. This pH range ensures crop safety while achieving high nutrient availability and prevents precipitation of calcium and magnesium in the drip irrigation line.
The urea phosphate product can reduce the pH of alkaline soil, inhibit the volatilization of ammonia nitrogen, increase the activity of calcium, magnesium and iron, and improve the utilization of nutrients, which is called a tool for chemically improving saline soil. Many research institutes and manufacturers at home and abroad are using the urea phosphate as a functional raw material to construct high-efficiency fertilizer for the transformation of alkaline soil. This high-efficiency fertilizer may be solid water soluble fertilizer, liquid water soluble fertilizer, or solid compound fertilizer. Phosphate urea fertilizer will become a new force in chemical methods to improve alkaline soils.