The soil's physical and chemical properties determine its ability to transport as well store water and nutrients. In the next few paragraphs we will try to explain the soil and water relationship, and the mechanisms by which moisture is transported and stored within the soil. Capillary moisture is the primary force in spreading the water horizontally and it is a primary source of water to the plant. Gravitational water is free water in the soil which will move downward under the influence of gravity. After the soil is saturated, the gravitational water will percolate downwards, leaving the soil at field capacity.
Field capacity is a measure of the water held by the soil against the influence of gravity.
If soil is saturated by rainfall or irrigation and then allowed to drain freely for 24 hours, the soil is usually at field capacity. For most plants, a soil moisture content near field capacity is the ideal moisture level for vegetative growth, because there is a good balance between soil moisture tension and aeration. The soil will lose very little water after it has drained to field capacity if there are no plants growing in it. Plants will remove water by transpiration and reduce the soil moisture. On hot days, the plants may use water faster than the soil can supply the roots, or faster than the roots can supply the rest of the plant and the plant will wilt.