Correct Answer - Option 1 : Duty
Duty: Relationship between volume of water and area of crop it matures . It is define as the area irrigated per cumec of discharge running for base period.
Crop period: It is the time in days, that a crop takes from The instant of its sowing to that of its harvesting.
Base period: The base period is the relation between he First watering and the last watering supplied to the land.
Delta: It is the total depth of water required by a crop during the entire base period.