Water by feel - click to enlarge
Soil water definitions
Field capacity (FC) is the amount of soil moisture held in soil after excess water has drained away and the rate of downward movement has materially decreased, which usually takes place within 2–3 days after a rain or irrigation in previous soils of uniform structure and texture.
Permanent wilting point (PWP) is defined as the soil moisture level below which moisture is unavailable to the plant (Sunflower used as the reference)
Available moisture (AM) is the soil moisture held between FC and PWP.
Available moisture before stress. This value varies with plant species, but is typically approximately half total available moisture
Video - When should I irrigate?
Laboratory methods. : The American Society of Agronomy have a series of excellent publications outlining laboratory methods for soil analysis Link