Field capacity is reached 24–48 hours after heavy rain or irrigation, when gravitational water has drained and only capillary-held water remains in soil pores. Clay soils retain more (35–40% by volume) than sandy soils (10–15%).
Between field capacity and the permanent wilting point (where plants can no longer extract water) lies the plant-available water. The agricultural water balance calculates when soil falls below field capacity to schedule irrigation.