Certified Crop Advisor Practice Exam

If a soil has an EC of 0.6 siemens per meter and contains 20 percent sodium on the CEC, it is a ______ soil.

1. saline

2. sodic

3. saline-sodic

4. acid

The correct answer is: saline-sodic

A soil characterized by an electrical conductivity (EC) of 0.6 siemens per meter and containing 20 percent sodium on the cation exchange capacity (CEC) is classified as saline-sodic. This classification is important because it indicates that the soil has excess sodium as well as elevated salts. Saline soils typically have a higher EC, generally above 4 decisiemens per meter, which is not the case here. On the other hand, sodic soils usually have less soluble salts, evidenced by a low EC, and a high percentage of sodium relative to the total cations in the soil. While this soil does have a significant percentage of sodium, its EC indicates that it also contains salts, hence it does not fit the purely sodic category. The combination of having a moderate EC and a notable amount of sodium leads to the classification of this soil as saline-sodic. This classification implies that while there are soluble salts present, which are contributing to the salinity, there is also a considerable amount of sodium that could affect the soil's physical properties and fertility. Recognizing this distinction is critical for managing soil health and crop productivity effectively.