The portion of a rainfall that infiltrates into the soil and is stored for plant use in the crop root zone. During a rainfall event, part of the rain will run off the surface of the soil, get trapped in the foliage, or percolate through the bottom of the root zone. This water is not available for plant growth and, therefore, is not considered to be effective rainfall. Effective rainfall is generally expressed as a depth of water over a unit area (e.g. in/acre).