Urea vs Ammonium Sulphate: Which Nitrogen Fertilizer Is Right for Your Crop?

Urea and ammonium sulphate (AS) are two of the most widely used nitrogen fertilizers for oil palm, rubber, paddy, vegetables and fruit crops in Malaysia. Both supply nitrogen, but they behave differently in the field. Understanding the differences helps you get more from every ringgit spent on fertilizer.

Quick comparison

• Nitrogen content: urea contains 46% N; ammonium sulphate contains about 21% N.
• Sulphur: ammonium sulphate also supplies about 24% sulphur; urea contains none.
• Nitrogen loss: urea is more prone to losing nitrogen to the air (volatilisation) when spread on the surface; AS is much less prone to this.
• Effect on soil pH: both acidify soil over time, but AS has a stronger acidifying effect.
• Handling: urea absorbs moisture readily and must be kept dry; AS is less hygroscopic.

Urea: the most nitrogen for the money

At 46% N, urea delivers more than twice the nitrogen of AS per bag, which usually makes it the cheapest source per kilogram of nitrogen and reduces transport and labour costs. Its weakness is volatilisation: when urea sits on warm, moist soil surfaces, a significant share of the nitrogen can escape as ammonia gas. Losses are generally higher on alkaline soils and in hot, humid conditions, which are common in the tropics.

Ways to reduce urea losses: incorporate it into the soil where practical, apply before light rain rather than onto wet surfaces in hot sun, split the total amount into smaller, more frequent applications, and avoid applying on soils with high pH.

Ammonium sulphate: nitrogen plus sulphur

AS supplies nitrogen in a form that is much less prone to volatilisation, so more of what you apply stays available to the crop. It also supplies sulphur, which many crops need for protein formation and which is increasingly deficient in intensively farmed soils. The trade-offs are a higher cost per kilogram of nitrogen and a stronger acidifying effect, which may require liming on soils that are already acidic.

How to decide

• Choose urea when cost per unit of nitrogen matters most and you can apply it in ways that limit losses.
• Choose ammonium sulphate when your soil is low in sulphur, when volatilisation losses are a concern, or on alkaline soils.
• Use both: many growers combine them, using urea for the bulk of nitrogen and AS to supply sulphur.

The best choice always depends on your soil, crop and local conditions. A soil and leaf analysis, together with advice from an agronomist or agricultural extension officer, is the most reliable way to set rates and timing.

Don’t forget potassium

Nitrogen is only part of the picture. Crops such as oil palm, fruits and vegetables also need potassium for yield and quality. Potassium sulphate supplies potassium and sulphur without chloride, which suits chloride-sensitive crops.

Buy fertilizers in bulk in Malaysia

MDNR Resources supplies urea fertilizer N46, ammonium sulphate and potassium sulphate for plantations, farms and distributors across Malaysia. Send your quantities and delivery location through our Request a Quote form.