What does it mean when all air spaces between soil particles are filled with water?

The scenario described, where all air spaces between soil particles are filled with water, is referred to as saturation. When saturation occurs, the soil is unable to hold any more water, which can affect the growth of plants and the activity of soil organisms. In a saturated state, the oxygen that is typically held in the soil voids is displaced by water, potentially leading to anaerobic conditions that can hinder root respiration and overall soil health.

This concept distinguishes itself from aeration, which refers to the presence of air in the soil. Drainage pertains to the process of removing excess water from soil, while hydration generally refers to the addition of water to a substance, not specifically the state of the soil in terms of air space and water content. Therefore, saturation is the most accurate term for the condition described, as it captures the idea of the soil being fully occupied by water at the expense of air.