Agronomy Degree Practice Exam

In a guaranteed analysis of fertilizer labeled 13-13-13, what does the first number represent?

1. Nitrogen

2. Sulfur

3. Phosphorus

4. Potassium

The correct answer is: Nitrogen

In a guaranteed analysis of fertilizer labeled 13-13-13, the first number represents the percentage of nitrogen present in the fertilizer formulation. Nitrogen is a crucial nutrient for plant growth, as it is a key component of amino acids, proteins, and chlorophyll, which are vital for photosynthesis. The balanced formulation of 13-13-13 indicates that this fertilizer contains an equal ratio of nitrogen, phosphorus, and potassium, which are the three primary macronutrients essential for plant health. Each number refers to the nitrogen, phosphorus (as P2O5), and potassium (as K2O) content, respectively. Understanding the roles of these nutrients helps in selecting appropriate fertilizers for different plant stages and types, ensuring optimal growth and yield.