Water Saturation Limits of Soil

Testing

• Pick up a large handful of soil and close your fist tight around it. If water comes out through your fingers, the soil is saturated. All of the available air space in the soil has been taken up by water.

Moisture-Holding Capacity

• The moisture-holding capacity of a field is how much water the soil is able to hold before it becomes saturated. Water beyond that point is called gravitational water because it simply travels through the soil to the water table. Plants do get some of the gravitational water as it moves past their roots, but generally speaking the moisture-holding capacity of soil is the key to understanding how much water is available to plant life. Moisture-holding capacity is expressed in terms of inches of water available per foot of soil.

Saturation Points

• The amount of water that soil can absorb is based on how much air space is available in that particular soil type. Because soil types vary based on depth, you have to think about the different layers throughout the root depth to understand how much water is actually available. Sand reaches its total saturation point at 5.2 inches per foot of water, while loam can absorb 5.8 inches per foot before saturation occurs.

Results of Saturation

• The result of ongoing soil saturation is not positive for plants growing in that soil. Plant roots need air as well as water in order to thrive. When all the available air space is taken up by water, the roots can actually suffocate. Also, harmful gasses that normally pass through the soil become trapped around roots, causing plant damage. Salt may also accumulate on the surface and increase the salinity of the soil, which is deadly to certain plants.