NPK 15-15-15

NPK 15-15-15 is the most widely used balanced compound fertilizer in the world, and its appeal is operational rather than agronomic: one product, one pass, all three major nutrients.

Compound, not blend

This is a genuine compound — every granule contains nitrogen, phosphate and potash, chemically combined during manufacture. That matters more than it sounds. A physical blend of three separate materials can segregate during handling, shipping and spreading, so different parts of the field receive different ratios. A compound cannot.

For an importer, this also means the material survives a long sea voyage and multiple handling points without changing.

Where it fits

As a base dressing before or at sowing, when a soil test does not point strongly in any one direction. Most programmes then top-dress nitrogen separately during the season — urea is the usual choice — and, for fruiting crops, add potassium as demand rises.

What a balanced ratio is not good at is matching a crop’s changing requirement. Potassium demand climbs steeply during fruit fill while nitrogen demand often falls — see NPK 11-8-34 + TE for that stage.

Buying considerations

• Nitrogen form split. The balance between ammoniacal and nitrate nitrogen affects how quickly the crop responds and how the root-zone pH moves.
• Granule size and hardness, which determine spreading width and resistance to breakdown.
• Sulphur content, often present and increasingly valuable as atmospheric deposition has fallen.

Our guide to reading NPK ratios explains how to compare this against straight fertilizers on cost per unit of nutrient.