The sodium absorption rate (SAR) is a comparison of the concentration of sodium ions (Na⁺) to that of calcium ions (Ca⁺²) and magnesium ions (Mg⁺²) and is considered with the electroconductivity measurement of salinity when assessing the potential effects of water quality on soil water penetration.

soil horizon

an approximately horizontal layer of soil differing from adjacent layers in physical, chemical, or biological properties such as color, structure, texture, consistence, kinds and numbers of organisms present, or degree of acidity or alkalinity.

solum

the upper horizons of the soil profile in which the natural processes of soil formation take place; true soil. The solum is where most plant roots grow.

tailwater

irrigation water that reaches the lower end of a field. Tailwater ratio is an indication of irrigation water application systems; tailwater return systems increase efficiency of surface water irrigation systems.

turgor

the normal state of turgidity and tension in plant cells caused by water pressure when plant cells are full of water. This pressure keeps stems upright and leaves expanded to receive sunlight.

turgor pressure

the pressure developed as the result of fluid in a turgid (swollen) plant cell caused by the osmotic diffusion toward the inside of a cell. Saline soil environments can affect the necessary plant cell turgor pressure by disrupting the osmotic balance.

vadose zone

the unsaturated zone of the soil above the permanent groundwater level. The vadose zone is of concern in considering the potential contamination, transport, degradation, and mobilization of nutrients, pesticides, salts, and trace elements.

water-holding capacity

the capability of soils to store and release available water to plants. Estimation of water-holding capacities are made using regression models from parameters such as particle size distributions, organic matter content, and bulk density.