What Is SA Fertilizer? Benefits, How to Apply and Precautions

SA fertilizer is a nitrogen fertilizer that many farmers in the Mekong Delta use for rice and vegetables, especially on sulfur-deficient soil. This article explains what SA fertilizer is, its benefits, how to apply it correctly and what to watch out for so the soil does not become acidic.

What is SA fertilizer?

SA fertilizer (ammonium sulfate, formula (NH4)2SO4) is a crystalline nitrogen fertilizer, usually white or slightly off-white. It contains about 20–21% nitrogen (N) and 23–24% sulfur (S). The nitrogen in SA is in ammonium form, so plants absorb it quickly and less of it volatilizes than urea when spread on the field surface.

Benefits of SA fertilizer for crops

• Supplies nitrogen: keeps leaves green and supports tillering and stem and leaf growth.
• Supplies sulfur: sulfur helps the plant build protein, keeps leaves evenly green and improves crop quality. Brassicas, onions, garlic, rice and oil crops need a lot of sulfur.
• Suits alkaline and low-sulfur soil: the fertilizer is mildly acidifying, so it helps improve slightly alkaline soil.

How to apply SA fertilizer correctly

• Rice: use it as a top-dressing at tillering, replacing part of the urea. See the stage-by-stage schedule in the article Nutrient management for rice by growth stage.
• Vegetables: top-dress once the plants have rooted, split into several small doses; it can be dissolved in irrigation water.
• Fruit trees: use it when new shoots emerge, together with potash and phosphate fertilizer.

The exact rate depends on the soil type, variety and crop stage. Farmers should ask an agronomist or a nearby dealer for a rate that suits their own field.

Precautions when using SA fertilizer

• Do not apply it season after season on acid sulfate or acidic soil: SA makes the soil more acidic. Combine it with lime or organic fertilizer to balance the pH. See the article Which fertilizers can make soil acidic.
• Do not mix it with lime or alkaline fertilizers before applying, because the nitrogen will volatilize.
• Store it in a dry place: SA absorbs moisture easily and cakes.

How is SA fertilizer different from urea?

Because its nitrogen content is lower, farmers need to apply roughly twice as much SA as urea to supply the same amount of nitrogen.

SA as a raw material for NPK production

Besides direct application, SA is also a raw material for blending NPK fertilizer. Factories and producers that need a stable supply of SA can see the Imported fertilizer raw materials page of Viet Nga Fertilizer.