Understanding Soil Water Holding Characteristics
Understanding Soil Water Holding Characteristicsz
The table below shows the plant available water held by different textured soils when they are fully wet.
Deciding when to irrigate should be based largely on soil moisture depletion by plants. Plants withdraw soil moisture to meet their evapotranspiration (ET) demands. Thus, the ET rate determines how much and how fast water is taken up from the soil by plants. It becomes more and more difficult for plants to withdraw water as the soil becomes drier, until the plants can no longer withdraw soil moisture and then they die (permanent wilting point is reached). Water must be added to the soil before it dries to this point in order to keep plants performing well.
Soils that can store greater amounts of moisture available to plants do not need to be irrigated as frequently as soils that store less. In general, sandier (light textured) soils need to be irrigated more frequently than soils with a greater clay content (heavier textured). A given plant will use water at the same rate in either soil but it will run out of water sooner in a sandier textured soil.
Plant-available water holding capacities of various textured soil.
| | Plant-Available Water Holding Capacity (inches of water per foot of soil) |
| Very coarse sands | 0.4 - 0.75 |
| Coarse sands, fine sands, loamy sands | 0.75 - 1.25 |
| Sandy loams, fine sandy loams | 1.25 - 1.75 |
| Very fine sandy loams, loams, silt loams | 1.50 - 2.30 |
| Clay loams, silty clay loams, sandy clay loams | 1.75 - 2.50 |
| Sandy clays, silty clays, clays | 1.60 - 2.50 |
zAdapted from:
Schwankl, L.J. and T. Prichard. 2009. University of California Drought Management Web Site. http://UCManageDrought.ucdavis.edu. Viewed Aug. 13, 2009.