Measuring and modeling ammonium adsorption by calcareous soils

Area of Science:

• Soil Science
• Environmental Chemistry
• Agricultural Science

Background:

• Ammonium (NH4+) is a key nutrient in agriculture but can be lost from soils.
• Understanding ammonium adsorption is crucial for efficient fertilizer use and environmental protection.
• Calcareous soils present unique challenges for nutrient retention due to their chemical properties.

Purpose of the Study:

• To assess ammonium (NH4+) adsorption isotherms in agricultural calcareous soils.
• To model NH4+ adsorption using a mechanistic exchange model.
• To identify factors influencing NH4+ adsorption in these soils.

Main Methods:

• Collected ten surface soil samples from Hamedan, Iran.
• Conducted batch adsorption experiments using varying NH4+ concentrations (0-150 mg NH4+ L-1) with 0.01 M CaCl2.
• Fitted empirical models (e.g., Freundlich) and used the PHREEQC program with a cation-exchange model for simulation.

Main Results:

• Adsorbed NH4+ amounts ranged from 8.95% to 35.23%.
• Adsorption correlated positively with soil pH, cation-exchange capacity (CEC), calcium carbonate, and clay content.
• Adsorption correlated negatively with sand content.

Conclusions:

• The cation-exchange model accurately simulated NH4+ adsorption in the studied soils.
• Cation-exchange capacity (CEC) was the dominant factor controlling NH4+ adsorption.
• Cation exchange is the primary mechanism governing NH4+ adsorption in these calcareous soils.