The decision of when to irrigate is often determined by the degree of soil moisture depletion. The crop withdraws soil moisture to meet its evapotranspiration (ET) demands. It becomes more and more difficult for the crop to withdraw water as the soil becomes drier, until the plant can no longer withdraw soil moisture and dies (permanent wilting point).
Soils that can store greater amounts of available water (stored soil moisture available to the plant) 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).
|Soil Texture||Available Waterholding capacity
(in. of water/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|