Final answer:
After a rainstorm, water that the soil retains against the force of gravity is known as field capacity. This level is crucial for plants because it indicates the usable water storage within the soil, with sandy soils having lower and clay soils having higher field capacities.
Step-by-step explanation:
After a rain, some of the water in soil drains by gravity. The amount of water left is called field capacity. Field capacity is the amount of water soil can hold against the force of gravity. The water between field capacity and the permanent wilting point is critical for plants, as it represents the useful storage capacity of the soil. Sandy soils have larger pores, allowing gravity to pull more water out and therefore have a lower field capacity compared to clay soils, which retain more water due to smaller pore sizes. The ideal agricultural soils are typically loams, which contain both sand and clay, providing a balance between water retention and drainage.