What are anion exchange sites in soil primarily responsible for?

The primary role of anion exchange sites in soil is to hold negatively charged ions. In soil chemistry, anions are negatively charged ions such as nitrate, phosphate, and sulfate. These anions, due to their charge, have a tendency to repel one another and are attracted to positively charged sites on soil particles, which are typically associated with cation exchange capacity.

The ability of soil to hold anions is influenced by several factors, including the soil's pH and the composition of soil mineral particles. Anion exchange capacity can vary widely among different soil types, with organic matter generally enhancing this capacity. A soil that effectively retains anions is crucial for plant nutrition as it determines the availability of essential nutrients.

While other aspects of soil health and function, such as cation exchange sites and microbial activity, are important for overall soil fertility and health, anion exchange sites specifically focus on the interaction and retention of negatively charged ions. This makes option B the most accurate choice in addressing the responsibility of anion exchange sites within the soil.