At deeper depths in ridge soils where there is less organic matter, field capacity values can be as low as four to six percent. Permanent wilting point is the soil water content at which plants remain wilted overnight or in a humid atmosphere. It is considered to be the point where plants cannot extract more water from the soil. Hence, plants remain wilted and will not recover from the wilt unless water is added. Average permanent wilting point values in the rooting zone for ridge sands range from 0.4 to 2.5 percent and 1.5 to five percent for flatwoods soils.
Available water is the amount of water between field capacity and the permanent wilting point.
The relationships among field capacity, permanent wilting point and available water for sand, loam and clay soils are shown in Figure 1. Notice that the darkened area, which represents available water, is very small in sands and much larger in loams and clays. Figure 1 illustrates how notoriously low the amount of available water is in Florida sands. Part of the reason for the low available water in Florida sands is the very low amount of organic matter and clay that sands contain. Citrus is grown in Texas and California on loam and clay soils that have two to three times the water holding capacity of Florida sands.