What soil property influences nutrient availability and pH buffering?

• A. Soil pH and Cation Exchange Capacity (CEC)
• B. Soil moisture
• C. Soil texture
• D. Soil salinity

Answer: (A)

The important idea is that nutrient availability is governed by soil chemistry, especially how the soil holds and releases cations and how soluble those nutrients are at a given pH. Plant nutrients mainly exist as positively charged ions, and their solubility—and thus availability to roots—depends on the soil’s pH. At different pH levels, some nutrients become more soluble while others bind to soil particles and become less available. The soil’s Cation Exchange Capacity (CEC) measures how many positively charged sites on clay minerals and organic matter can hold nutrient cations. A higher CEC provides more exchange sites to hold nutrients and to swap in and out ions, which buffers or resists changes in soil pH. This buffering action helps keep nutrient availability relatively stable even when acids or bases are added to the soil. So, soil pH and CEC together best explain how nutrients are available to plants and how the soil buffers pH fluctuations. While moisture, texture, or salinity influence other aspects of nutrient dynamics, they don’t address both availability and buffering as directly as pH and CEC do.