Urea phosphate (CO(NH2)2·H3PO4), also known as urea phosphate or phosphoric urea, is a phosphoric acid complex salt with an amino acid structure formed by equimolar reaction of phosphoric acid and urea. Urea phosphate appears as colorless transparent prismatic crystals with a parallel layered structure. It has a molecular weight of 158.06, density of 1.74g/cm3, melting point of 115–117℃, nitrogen content of 17.7%, phosphorus content (P2O5) of 44.9%, and a pH value of 1.89 for a 1% aqueous solution.
Urea phosphate is produced through the reaction of urea and phosphoric acid, expressed by the equation: H3PO4+CO(NH2)2→CO(NH2)2·H3PO4.
The production process can be categorized into thermal phosphoric acid method and wet phosphoric acid method based on the source of raw materials. The former has higher phosphoric acid concentration with fewer impurities but is more expensive, resulting in higher costs for producing phosphoric enzyme. The latter has lower phosphoric acid concentration with more impurities but is cost-effective. Currently, foreign producers generally use the wet phosphoric acid method, while Chinese manufacturers use both methods, with the former being more prevalent.
One of the crucial applications of urea phosphate in China is as a non-protein nitrogen feed additive for ruminant animals like cattle and sheep. The common phenomenon of "strong cattle and sheep" in the current market is often associated with urea phosphate used as a feed additive.
Additionally, urea phosphate serves as a novel and efficient nitrogen-phosphorus compound fertilizer, demonstrating significant effects on increasing crop yields and improving soil quality.
Effect of Urea Phosphate Application on Soil:
pH Control:
Urea phosphate can regulate soil pH. In acidic red soil and alkaline loamy soil, the hydrolysis of conventional urea under urease action results in an increase in soil pH. In acidic soils, the pH increase is beneficial for reducing aluminum toxicity to plants. However, in calcareous soils, especially alkaline soils, the pH increase is detrimental to soil physicochemical properties, structure, plant growth, and agricultural production. With a pH of 1.89 for a 1% aqueous solution, urea phosphate, when applied as a soil conditioner and fertilizer, can moderately reduce the pH of the soil or soil microzones, altering the soil acid-base balance and thereby improving soil physicochemical properties, structure, and promoting crop growth.
Reduction of Ammonia Volatilization:
Urea phosphate can decrease soil ammonia volatilization. Ammonia volatilization is a major pathway for nitrogen loss in soil. Reducing ammonia volatilization is crucial for improving nitrogen fertilizer utilization. Urea phosphate, as an acid fertilizer, can effectively reduce soil pH, thereby reducing ammonia volatilization and enhancing fertilizer efficiency. Moreover, urea phosphate can lower the hydrolysis rate of urea, decreasing the ammonium nitrogen content in the soil and effectively reducing soil ammonia volatilization.
Activation of Calcium and Magnesium in Soil, Enhancing the Effect of Trace Elements:
Calcium, magnesium, manganese, and zinc are essential nutrients for plant growth and development. In calcareous soils, these elements may exist in large quantities, but their availability is limited due to the high pH and the presence of OH- ions, leading to the formation of insoluble precipitates. Urea phosphate, as an acidic chelating nitrogen-phosphorus compound fertilizer, can increase the hydrogen ion concentration in soil, reducing soil pH and enhancing the solubility of calcium, magnesium, zinc, manganese, and other elements. Additionally, urea phosphate can form soluble phosphate complexes with calcium and magnesium in the soil, promoting the absorption of phosphorus and trace elements by plants and increasing their bioavailability.
Urea Phosphate Effects in Other Agricultural Aspects:
Benefits on Agricultural Production:
The primary purpose of applying fertilizers in agriculture, especially chemical fertilizers, is to increase yield and income. Compared to other conventional nitrogen-phosphorus fertilizers and their compound fertilizers, urea phosphate can significantly increase the economic benefits of fertilization. According to relevant experiments, it was found that cotton application of urea phosphate compared with the customary fertilizer, not only can reduce cotton boll shedding, increase the weight of a single boll, so that the yield is greatly improved, the economic benefits of a significant increase.
Impact of Urea Phosphate on Soil Microorganisms from the Application of Farmyard Manure:
The application of farmyard manure and other organic substances to the soil effectively improves soil physicochemical properties and nutrient levels. However, these organic materials may contain harmful microorganisms to humans or plants. Because urea phosphate can improve the sanitary conditions of fertilized soil, enhancing the community structure and biological activity of ammonia-oxidizing bacteria, nitrite-oxidizing bacteria, decomposing bacteria, and nitrogen-fixing bacteria, urea phosphate can be used as a soil disinfectant in fertilized soils.
Effect of Urea Phosphate on Drip Irrigation Facilities:
Drip irrigation is a major solution to address water scarcity. For hard water with a pH exceeding 7.5, dissolved substances such as calcium and magnesium in the water may precipitate, posing a risk of clogging drip irrigation facilities at locations such as filters, pipes, and filter cartridges. Urea phosphate, being acidic in aqueous solution, increases the solubility of calcium and magnesium ions. Simultaneously, urea phosphate interacts with calcium and magnesium ions in aqueous solution, forming soluble urea phosphate calcium and urea phosphate magnesium, reducing, or preventing the precipitation of calcium and magnesium. This lowers scaling and clogging in drip irrigation systems, thereby extending the system's lifespan.
In conclusion, urea phosphate is an excellent nitrogen-phosphorus compound fertilizer with chelating properties, soil calcium-magnesium activation, and alkaline soil structure improvement effects. Therefore, using urea phosphate as the basic fertilizer source for drip irrigation can bring significant ecological and economic benefits.
With the adoption of wet urea phosphate production technology and continuous production methods, the cost of urea phosphate products will significantly decrease, making it more competitive and feasible in soil improvement for agricultural production. Urea phosphate, as a basic fertilizer, can be used in conjunction with other organic, inorganic, organic-inorganic compound fertilizers, and trace element fertilizers, making it widely applied and promoted.
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