Application issues with ammonium nitrate:\nWhy is ammonium nitrate commonly mixed with limestone (e.g., as CAN) and not used “as-is” as a straight fertilizer?

Introduction / Context:
Ammonium nitrate (AN) is a high-nitrogen fertilizer with desirable agronomic properties, but it presents handling and safety challenges. Many markets offer it as calcium ammonium nitrate (CAN), where limestone or dolomite reduces caking, hygroscopicity, and explosive potential. Understanding the reason for blending clarifies logistics and regulatory practices.

Given Data / Assumptions:

• Considering bulk storage, transport, and field application at ambient temperature.
• Fertilizer-grade AN vs. stabilized/conditioned forms.
• Standard safety and moisture conditions encountered in warehouses.

Concept / Approach:
Pure ammonium nitrate readily absorbs moisture (hygroscopic), leading to caking and handling difficulties. More critically, under certain confinement and contamination conditions it can undergo rapid decomposition and detonation; blending with limestone dilutes AN, reduces sensitivity, and improves physical stability. The blend also buffers acidity upon soil application. AN is a solid at room temperature, and its nitrogen content is actually high (about 33–35%); therefore, low content or “liquid” state are not the governing issues.

Step-by-Step Solution:

Verification / Alternative check:
Industry guidance and regulations often restrict pure AN storage; CAN is widely permitted due to reduced hazard classification and better physical properties.

Why Other Options Are Wrong:

• “Highly acidic”: AN solutions are mildly acidic, but acidity is not the primary reason for not using AN straight.
• “Liquid at room temperature”: false; AN is a crystalline solid.
• “Very low nitrogen content”: incorrect; AN is ~35% N.
• “Phytotoxic at any dose”: untrue when applied at recommended rates.

Common Pitfalls:
Confusing agronomic considerations with safety/handling realities; overlooking national regulations that target pure AN due to security and accident history.

Final Answer:
It is hygroscopic and explosive in nature, creating storage and safety hazards.