Urea Phosphate: Combining N–P Nutrition with Acidification

As fertigation, drip irrigation, and precision nutrient management continue to develop, the value of fertilizer raw materials is no longer determined solely by how much nutrient they provide. Solubility, pH regulation, compatibility, and adaptability to irrigation systems have become equally important.

Urea Phosphate (UP) is a representative example of this type of functional fertilizer ingredient.

Formed from urea and phosphoric acid, it is commonly expressed as 17-44-0 in terms of nutrient analysis. It provides both nitrogen and phosphorus while offering strong acidifying capacity. Thanks to its high water solubility and low solution pH, Urea Phosphate is particularly suitable for alkaline soils, hard-water irrigation areas, high-value horticultural crops, and modern drip fertigation systems.

1. Basic Information on Urea Phosphate

Item	Typical Specification / Description
Chemical Name	Urea Phosphate
Molecular Formula	CO(NH₂)₂·H₃PO₄
Molecular Weight	158.06 g/mol
Appearance	White or colorless crystals
Nitrogen (N)	Approx. 17–18%
Phosphorus (P₂O₅)	≥44%
Water Solubility	Highly soluble in water
pH (1% aqueous solution)	Approx. 1.6–2.0
Relative Density	Approx. 1.62
Thermal Stability	Gradually decomposes upon heating
Biuret	A key quality parameter for agricultural grades; low-biuret grades are available
Key Characteristics	High solubility, strong acidity, integrated N and P supply

The key differentiation of Urea Phosphate is not simply its N + P content, but its ability to provide:

Nitrogen supply + phosphorus supply + acidification + improved irrigation/fertigation conditions.

It is therefore better understood as a functional phosphorus source, rather than merely a conventional phosphate fertilizer.

2. How Is Urea Phosphate Produced?

Urea Phosphate is primarily produced through the reaction of urea with phosphoric acid:

CO(NH₂)₂ + H₃PO₄ → CO(NH₂)₂·H₃PO₄

A typical production process includes:

Raw material preparation → reaction → concentration/adjustment → cooling crystallization → solid-liquid separation → drying → screening → packaging

Although the overall production process is relatively straightforward, several critical parameters must be carefully controlled to obtain a product suitable for premium water-soluble fertilizers, drip irrigation, or even foliar formulations.

1. Raw Material Purity

Biuret in urea, as well as metal ions and suspended impurities in phosphoric acid, can directly affect the quality of the finished product.

2. Reaction Temperature

Reaction and concentration temperatures must be properly controlled. Excessively high temperatures or prolonged exposure to heat may promote urea condensation and increase biuret formation.

3. Raw Material Ratio

Proper control of the urea-to-phosphoric-acid ratio helps improve reaction efficiency, minimize residual free acid or unreacted urea, and improve crystallization quality.

4. Crystallization Control

Cooling rate, concentration, and crystallization conditions influence crystal size, flowability, moisture content, and subsequent storage stability.

5. Mother Liquor Recycling

Recycling mother liquor can improve raw material utilization, but impurity accumulation must be carefully managed to avoid affecting final product quality and consistency.

3. Why Is Low Biuret Important?

For Urea Phosphate, biuret is one of the important quality indicators for agricultural applications.

Biuret is a by-product formed when urea undergoes condensation under elevated temperatures. Excessive biuret levels may increase the risk of phytotoxicity, particularly in foliar applications, concentrated fertilizer solutions, or sensitive crops.

Typical symptoms may include:

• Leaf yellowing or scorching;

• Damage to leaf tips and margins;

• Suppressed seedling growth;

• Physiological injury in sensitive crops.

For this reason, different customers may specify different biuret limits depending on whether the product is intended for fertigation, water-soluble fertilizer production, or foliar application.

Typical commercial positioning may be summarized as follows:

Product Grade	Biuret Control	Main Applications
Standard Agricultural Grade	≤0.9%	Water-soluble fertilizers, fertigation, general agricultural use
Low-Biuret Grade	≤0.5%	High-value crops, foliar fertilizers, premium liquid fertilizers
High-Purity Specialty Grade	≤0.3–0.5%	Specialized formulations with stricter impurity and safety requirements

Specific limits should always follow the regulations of the destination market, registration requirements, and individual customer specifications. There is no single universal biuret limit applicable to all markets.

4. Core Agricultural Value of Urea Phosphate

1. Simultaneous Nitrogen and Phosphorus Supply

Urea Phosphate typically provides approximately:

17% N + 44% P₂O₅

The nitrogen is mainly present in urea form, while phosphorus is supplied in a highly water-soluble form.

This nutrient combination is particularly suitable for:

• Seedling stages;

• Root establishment;

• Flower bud differentiation;

• Transplant recovery;

• Growth stages with high phosphorus demand.

2. Strong Acidifying Capacity

A 1% Urea Phosphate solution generally has a pH of approximately 1.6–2.0.

This gives the product particular value in alkaline soils and irrigation systems supplied with high-alkalinity water.

Proper reduction of root-zone or nutrient-solution pH can help:

• Improve the availability of certain forms of phosphorus;

• Improve the availability of micronutrients such as Fe, Zn, and Mn;

• Improve fertilizer performance under alkaline irrigation conditions;

• Reduce the risk of certain carbonate deposits;

• Improve the operating environment of drip fertigation systems.

For this reason, the Middle East, South Asia, and other regions with hard-water irrigation conditions are representative markets for Urea Phosphate applications.

5. Typical Agricultural Applications

Urea Phosphate is particularly suitable for:

Grapes, citrus, tomatoes, peppers, melons, berries, flowers, nursery plants, and other high-value horticultural crops.

It is especially suitable under the following conditions:

• Neutral to alkaline soils;

• Irrigation water with relatively high bicarbonate levels;

• Drip and micro-irrigation systems;

• Protected cultivation;

• High-value cash crops;

• Production systems where micronutrient-use efficiency is important.

Reference Application Methods

Application Method	Reference Concentration / Rate	Notes
Drip Fertigation	0.05–0.3%	Adjust according to water quality, crop requirements, and EC
Micro-sprinkler / Sprinkler Irrigation	0.1–0.2%	Ensure irrigation equipment has adequate acid resistance
Foliar Application	0.1–0.2%	Conduct a small-scale crop safety test before broad application
Root-Zone Application	2–5 kg/mu	Dilute sufficiently and adjust according to soil conditions
Water-Soluble Fertilizer Formulation	According to formulation design	Can serve as both a phosphorus source and an acidifying component

These figures are intended only as general technical references. Actual application rates should be adjusted according to crop species, growth stage, water quality, EC, temperature, and local agronomic conditions.

6. What Is the Difference Between Urea Phosphate and MAP?

Monoammonium Phosphate (MAP) and Urea Phosphate are both concentrated nitrogen-phosphorus fertilizers, but their application logic is not identical.

Comparison	Urea Phosphate (UP)	MAP
Typical Grade	17-44-0	12-61-0
Nitrogen Form	Urea-N	Ammonium-N
Solution Acidity	Strongly acidic	Mildly acidic
pH Adjustment Capacity	Strong	Relatively limited
Phosphorus Concentration	High	Higher
Suitability for Hard-Water Systems	Generally better	Requires attention to water quality and compatibility
Synergy with Micronutrients	More pronounced	Moderate
Main Advantage	Acidification + N/P supply	High-concentration phosphorus source
Typical Positioning	Precision fertigation and high-value agriculture	General water-soluble fertilizers and high-phosphorus formulations

Therefore, Urea Phosphate should not simply be viewed as a replacement for MAP.

Where higher phosphorus concentration and cost efficiency are the main priorities, MAP often has an advantage. Where the formulation also requires phosphorus, nitrogen, lower nutrient-solution pH, and improved performance under hard-water irrigation conditions, Urea Phosphate provides greater functional value.

The two products are better understood as functionally complementary phosphorus sources.

7. Formulation and Compatibility Value

Urea Phosphate can be used as a functional ingredient in water-soluble fertilizers, liquid fertilizers, and concentrated fertilizer formulations.

It can generally be incorporated into formulations containing:

• Potassium nitrate;

• Monopotassium phosphate;

• Potassium sulfate;

• Magnesium sulfate;

• EDTA/EDDHA-chelated micronutrients;

• Selected water-soluble micronutrients.

However, special attention is required when formulating with calcium and magnesium.

Calcium and Magnesium Systems

Although Urea Phosphate has strong acidifying properties, it is still fundamentally a phosphate-containing system.

At high concentrations, phosphate ions may react with Ca²⁺ and Mg²⁺ to form poorly soluble phosphate salts.

Therefore, it is incorrect to assume that:

“Because Urea Phosphate is acidic, it can be freely mixed with calcium fertilizers.”

Compatibility should instead be evaluated according to concentration, pH, water quality, temperature, and mother-solution composition.

8. Applications in Animal Feed

Feed-grade Urea Phosphate that complies with the relevant feed regulations and quality standards may be used in certain ruminant nutrition systems to provide both:

• Phosphorus;

• Non-protein nitrogen (NPN).

Rumen microorganisms can utilize non-protein nitrogen for microbial protein synthesis, giving Urea Phosphate potential value in certain cattle, sheep, and other ruminant feeding systems.

However, an important distinction must be made:

Agricultural-grade Urea Phosphate must not automatically be considered equivalent to feed-grade Urea Phosphate.

When used in animal feed, the product must comply with the applicable market requirements governing:

• Heavy metals;

• Fluorine;

• Biuret;

• Harmful impurities;

• Feed additive registration and permitted inclusion rates.

9. Storage and Handling Precautions

Because Urea Phosphate is strongly acidic, the following precautions should be observed during storage and use:

• Store in sealed, moisture-resistant packaging;

• Avoid prolonged exposure to high temperature and humidity;

• Ensure fertilizer preparation equipment has appropriate acid resistance;

• Conduct compatibility testing before preparing concentrated mother solutions;

• Avoid direct high-concentration mixing with strongly alkaline materials;

• Carefully evaluate precipitation risks when mixing with calcium- or magnesium-containing products;

• Control foliar concentrations carefully and conduct small-scale trials before full application.

Transport classification and hazard status should be determined according to the specific product SDS, packaging configuration, and applicable transport regulations in the destination country.

Conclusion

The value of Urea Phosphate goes far beyond simply providing 17% nitrogen and 44% phosphorus.

Its real competitive advantage lies in combining:

N–P nutrition, acidification management, high water solubility, and compatibility with modern irrigation systems within a single functional raw material.

For conventional broad-acre agriculture, MAP, DAP, and other phosphate fertilizers continue to offer clear advantages in terms of cost and nutrient concentration. However, in drip irrigation, protected cultivation, high-value horticulture, hard-water irrigation, and sophisticated water-soluble fertilizer formulations, Urea Phosphate offers a distinctly different functional profile.

As global agriculture continues to move from conventional fertilization toward precision water and nutrient management, Urea Phosphate is evolving from a simple nitrogen-phosphorus fertilizer into a functional phosphorus source and formulation tool for modern fertigation systems.

Urea Phosphate: Combining N–P Nutrition with Acidification