Which nutrient is represented by the first number on a typical N-P-K fertilizer label?

• A. Potash
• B. Nitrogen
• C. Phosphoric acid
• D. Lime

Answer: (B)

The key idea is that fertilizer labels show three numbers representing the percent by weight of the main plant nutrients, in the order nitrogen, phosphorus, and potassium. The first number specifically tells you how much nitrogen is in the mix. Nitrogen is the nutrient that drives leafy growth and dark green color because it’s a major building block of chlorophyll and amino acids. So, the first number indicates nitrogen content—the nutrient that promotes vigor in the foliage.

The middle number refers to phosphorus, which supports root development and energy transfer in plants, while the last number corresponds to potassium, which helps with overall plant health, water regulation, and stress resistance. Potash is another name often used for potassium, and lime is not part of the N-P-K trio; lime is a soil amendment used to adjust pH and is not listed as a nutrient on the N-P-K label.

So the nutrient represented by the first number is nitrogen.