Define soil salinity.

Soil salinity is defined as the concentration of soluble salts in the soil. This measure is crucial in understanding the soil’s ability to support plant growth, as high salt concentrations can lead to osmotic stress in plants, making it difficult for them to absorb water. Salinity can impact the availability of nutrients and can lead to issues such as soil structure degradation and reduced biological activity. It is commonly measured in terms of electrical conductivity, which indicates the amount of dissolved ions present in the soil solution.

Understanding soil salinity is particularly important in agricultural practices, as it informs decisions regarding irrigation practices, crop selection, and soil management strategies to mitigate salinity-related issues. The other options deal with different soil properties: moisture retention refers to the soil's ability to hold water, organic matter concerns the decomposed material that enriches the soil, and pH level indicates the acidity or alkalinity of the soil. Each of these properties plays a significant role in soil health, but they are distinct from the specific definition of soil salinity.