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difference between DAP and urea

In the process of promoting crop growth, nitrogen (N) and phosphorus (P) are two key nutrients required by plants. Among various types of fertilizers, DAP (diammonium phosphate) and urea are the two most commonly used and crucial nitrogen-phosphorus compound fertilizers, as well as nitrogen fertilizers.

If you are a farmer, gardening enthusiast, or agricultural practitioner, understanding the difference between diammonium phosphate (DAP) and urea is crucial for optimizing soil health, increasing crop yields, and improving nutrient utilization efficiency.

What is urea?

Urea, with the chemical formula CO(NH₂)₂, is a high-concentration nitrogen fertilizer typically containing 46% pure nitrogen (N). It is currently one of the largest and most widely used nitrogen fertilizers in the world, usually in the form of white granules or small balls.

Main features:

High nitrogen content: Urea has the highest nitrogen content among all solid nitrogen fertilizers, which means that with the same amount of nitrogen transported and stored, the volume and weight of urea are smaller, thereby reducing costs.
Good water solubility: Urea is easily soluble in water, and after dissolution, it will be hydrolyzed into ammonium nitrogen (NH ₄⁺) by urease in the soil, and then further converted into nitrate nitrogen (NO ∝⁻) for plant absorption.
Mechanism of action: After urea is applied to the soil, it takes some time to transform into a form that can be absorbed by plants. This transformation process is influenced by soil temperature, moisture, and microbial activity.
Applicable crops and application methods: Suitable for all crops, this product can be used as a base fertilizer, topdressing, or foliar spray.

Advantages:High nitrogen content, good cost-effectiveness, and convenient application.

Disadvantages: Easy to evaporate (especially if the surface is not covered with soil or irrigated in a timely manner), risk of leaching (nitrate nitrogen is easily lost through water movement), and minimal impact on soil pH.

What is diammonium phosphate (DAP)?

DAP (diammonium phosphate), chemical formula (NH₄)₂HPO₄, is an efficient compound fertilizer that provides both nitrogen and phosphorus, two essential macro elements for plants. Its typical nutrient content is 18% nitrogen (N) and 46% phosphorus pentoxide (P₂O₅), usually appearing as gray-white particles.

Main features:

Dual nutrient: DAP provides both nitrogen and phosphorus, with phosphorus being a key element for plant root development, flowering, fruiting, and energy conversion.
Water solubility: DAP is also a water-soluble fertilizer, which releases ammonium nitrogen and phosphate ions (HPO ₄² ⁻ and H ₂ PO ₄⁻) for plant absorption after dissolution.
Mechanism of action: Nitrogen in diammonium phosphate exists in ammonium form and is not easily volatile, but phosphorus is easily fixed in soil, and its effectiveness is affected by soil pH and minerals.
Applicable crops and application methods: It is particularly suitable as a base fertilizer and seed fertilizer for crops, especially during the sowing period or early stages of crop growth, to promote root development and seedling growth.

Advantages: Simultaneously providing nitrogen and phosphorus, with high effectiveness of phosphorus and low volatility of ammonium nitrogen.

Disadvantages: The nitrogen content is lower than that of urea, the cost is relatively high, and it is not suitable as the only topdressing (unless the crop also requires a large amount of phosphorus).

The core difference between DAP and urea

1.Nutrient composition (most critical difference)

The core difference lies in the different types of nutrients provided by the two fertilizers:

Urea: can be regarded as a “nitrogen fortifier”. It contains pure nitrogen elements and is suitable for crops that require rapid nitrogen supplementation, such as leafy vegetables like spinach or wheat in their vegetative growth stage.

Diammonium phosphate (DAP): It is a “dual nutrient versatile”. Simultaneously providing nitrogen (for branch and leaf growth) and phosphorus (for root and reproductive development), suitable for crops with high phosphorus requirements (such as corn, soybeans, or fruit trees during planting and flowering periods).

2.Effects on plant growth

Due to different nutrient compositions, there are significant differences in the effects of diammonium phosphate (DAP) and urea on plant growth:

The function of urea

Promoting branch and leaf development: Nitrogen is the core component of chlorophyll, which is a key pigment in photosynthesis. Urea can make crop leaves appear more lush and have a darker green color, which is crucial for crops harvested from leaves (such as lettuce and cabbage) or herbaceous plants (including lawns and grasses).
Supporting nutritional growth period: The best application effect occurs during the early to middle stages of crop nutritional growth, when plants primarily focus on leaf and stem development (such as before wheat heading and before tomato flowering).

The role of diammonium phosphate (DAP)

Promoting root establishment: Phosphorus is an essential nutrient for root growth, especially crucial for the development of seedling roots. Applying diammonium phosphate during sowing can help seedlings grow strong roots and enhance their ability to absorb water and nutrients (such as when sowing corn or transplanting tomatoes).
Supporting reproductive growth period: Phosphorus can provide energy for flowering, pollination, and the development of fruits and seeds. Ammonium phosphate is suitable for crops such as cotton, chili, and mango that require phosphorus to increase yield and quality.
Synergistic supply of nitrogen and phosphorus: The nitrogen in diammonium phosphate provides energy for plants to absorb phosphorus (which requires energy consumption), avoiding the problem of “phosphorus fixation” (i.e., phosphorus exists in the soil but cannot be absorbed by plants).

3.Impact On Soil pH Value

Both fertilizers can affect soil pH, but in opposite directions – this is a key factor to consider in soil health management:

Urea

Long-term neutral to slightly acidic: Urea itself is neutral (pH value is about 7), but it will release ammonia through urease decomposition in soil, which is then converted into nitrate by soil bacteria. This nitrification process produces a small amount of acidic substances, and long-term application can cause a slight decrease in soil pH (more pronounced in sandy and weakly buffering soils).
Suitable for most soils: not prone to causing drastic fluctuations in soil pH, suitable for neutral, slightly acidic, or slightly alkaline soils.

Diammonium phosphate (DAP)

Alkaline: diammonium phosphate contains ammonium ions and phosphate ions. When ammonium ions are absorbed or converted into nitrate by plants, the remaining phosphate ions will react with soil moisture to release hydroxide ions. Long-term application can lead to an increase in soil pH.
Suitable for acidic soil: The alkaline action of diammonium phosphate can neutralize acidic soil (pH<6.0) and enhance nutrient availability (such as in acidic soil areas, such as red soil). However, caution should be exercised when using alkaline soil (pH > 8.0), as it will further increase the pH value and reduce the effectiveness of trace elements such as iron and zinc.

4.Risk of nitrogen loss

The nitrogen loss risk of urea is higher than that of diammonium phosphate, which affects its nutrient utilization efficiency:

Urea: If not plowed into the soil, there is a high risk of volatilization loss (ammonia loss); In sandy soil, there is also a higher risk of nitrogen leaching and loss (nitrate loss with water) caused by rainfall or irrigation.

Ammonium phosphate (DAP): Low risk of nitrogen loss. The ammonium ions it contains are easily adsorbed by soil clay particles (reducing leaching), and the volatilization loss is minimal when applied correctly (such as buried in soil).

5.Cost and availability

Urea: The unit nitrogen cost is typically lower due to its high nitrogen content and large-scale production. Global supply is abundant, making it the preferred nitrogen fertilizer for small and large-scale agriculture.

DAP: The unit nitrogen cost is relatively high, but when the soil is deficient in both nitrogen and phosphorus, using DAP is more cost-effective (without the need to purchase two different fertilizers separately). In areas with an insufficient supply of phosphoric acid raw materials, its availability may be limited; however, it remains a widely circulated fertilizer in the international market.

When to choose urea and when to choose DAP?

Refer to the following guidelines and choose the appropriate fertilizer based on actual needs:

The situation of choosing urea:

The soil lacks nitrogen but has sufficient phosphorus content (to be confirmed through soil testing).
Planting crops that require a large amount of nitrogen (leafy vegetables, wheat, lawns, grasses).
We need to choose cost-effective nitrogen sources for large-scale farmland.
The soil is alkaline (the slightly acidic effect of urea does not exacerbate pH issues).
When pursuing the lowest unit nitrogen cost.

When choosing diammonium phosphate (DAP):

Soil is simultaneously deficient in nitrogen and phosphorus (this is common in newly cultivated soil or nutrient depleted soil).
In the sowing or transplanting stage, DAP can promote root growth.
Planting crops that require phosphorus to support flowering and fruiting (corn, soybeans, cotton, fruit trees).
The soil is acidic (the alkaline effect of DAP can balance the pH value).

conclusion

In summary, DAP and urea are both indispensable fertilizers in agricultural production, but their respective characteristics determine their optimal application scenarios. Urea is the preferred nitrogen supplement due to its high nitrogen content and cost-effectiveness, while DAP plays a crucial role in early crop growth and phosphorus management, providing a dual supply of nitrogen and phosphorus.

By conducting soil testing to understand the soil’s nutrient status, identifying crop requirements, and considering factors such as pH value and application timing, appropriate fertilizers can be selected to improve yield while maintaining soil health.

fAQ DAP AND UREA

Can diammonium phosphate (DAP) and urea be mixed for application?
Sure, but apply immediately after mixing (long-term mixing can cause clumping and nutrient loss). It is recommended to apply separately according to the growth period of crops (such as DAP during sowing and urea during tillering).

What kind of fertilizer is suitable for rice fields?
Priority should be given to urea (rice requires a large amount of nitrogen), but DAP can be applied during transplantation to promote root growth and development.

Does diammonium phosphate (DAP) contain potassium?
Not included. If the soil lacks potassium (K), nitrogen, phosphorus, potassium compound fertilizer (such as 10-20-20 NPK fertilizer) should be selected.

Can urea be used for flowering plants?
If the soil phosphorus content is sufficient, a small amount can be applied. If you need to promote flowering, it is recommended to use urea in combination with superphosphate (a phosphate source) or choose DAP directly.

Tech Blog

difference between DAP and urea

What is urea?

What is diammonium phosphate (DAP)?

The core difference between DAP and urea