Certified Crop Advisor Practice Exam

Which anion is most likely to leach from the soil?

1. Phosphate

2. NO3-

3. Sulfate

4. Chloride

The correct answer is: NO3-

Nitrate (NO3-) is the anion most likely to leach from the soil due to its chemical properties and behavior in the soil-water system. Nitrate is highly soluble in water and does not readily bind to soil particles because it carries a negative charge. This solubility means that when heavy rainfall or irrigation occurs, nitrate can easily move with the water through the soil profile and into deeper soil layers or surface water bodies. In agricultural settings, the application of nitrogen fertilizers often increases nitrate concentrations in the soil, making it particularly susceptible to leaching. This characteristic can lead to environmental concerns, such as groundwater contamination and the potential for eutrophication in aquatic ecosystems, highlighting the importance of managing nitrate applications carefully. Other anions such as phosphate tend to bind to soil particles and are less mobile, while sulfate and chloride can also leach but are generally less prominent than nitrate in terms of agricultural runoff and water quality issues. Nitrate's solubility and lack of strong binding to the soil matrix are key factors that contribute to its status as the most likely anion to leach from the soil.