What is duty of water in irrigation?

Duty of water is the area of land that can be irrigated with a unit discharge of water. Expressed in hectares per cumec (ha/m3/s). Higher duty means water is used more efficiently. Factors affecting duty: climate (evaporation losses), soil type (percolation), crop type (water requirement), conveyance efficiency, and irrigation method. Delta of water is total depth of water required by crop during growing season. Relationship: Duty = 8.64 * crop period (days) / Delta (cm).