What is the Cation Exchange Capacity of a soil?

The Cation Exchange Capacity (CEC) of soil refers to its ability to hold and exchange positively charged ions, known as cations, such as calcium, magnesium, potassium, and sodium. This capacity is crucial for maintaining soil fertility, as it allows for the retention and availability of essential nutrients for plant uptake. Soils with higher CEC can retain more nutrients and provide a more stable supply for plants, enhancing their growth and health.

In contrast, the other options either describe types of ions or processes that are not directly related to the capacity of the soil in holding and exchanging nutrients. Positive-charged ions and negative-charged ions pertain to the types of charges present in the soil but do not capture the essence of CEC. The removal of bases by water percolation speaks to nutrient leaching, which is an aspect of soil management but not the definition of CEC itself. Thus, understanding CEC is fundamental in soil science and agronomy as it directly influences nutrient availability for crops.