C. Salt.
Salinization refers to the buildup of salts in soil, which can have negative impacts on plant growth and soil fertility. This process occurs when water containing dissolved salts moves into the soil, either from natural sources such as seawater intrusion or irrigation water with high salt concentrations. Over time, this salt-rich water can accumulate in the soil, increasing the concentration of salts in the soil and leading to salinization. This can result in a decline in soil fertility, leading to reduced plant growth and crop yields. Additionally, high salt levels in the soil can also cause changes in the soil structure and texture, making it difficult for plants to absorb water and nutrients from the soil. Salinization is a major problem in many arid and semi-arid regions, where the limited amount of freshwater resources make it difficult to manage soil salinity levels.