High and low duty are terms used in the field of irrigation to describe the water requirement of crops. The term "duty" refers to the amount of water needed for a specific area of land, usually measured in hectares. It is an important parameter in irrigation design as it helps determine the size of irrigation systems and the amount of water that needs to be supplied.

The units used to define high and low duty are hectares/cumec. Let's understand what this means:

1. Hectares: Hectare is a unit of area commonly used in agriculture and land measurement. It is equal to 10,000 square meters or 2.47 acres. In irrigation, the duty is expressed in terms of the area of land being irrigated.

2. Cumec: Cumec is short for cubic meter per second. It is a unit of flow rate commonly used in hydrology and irrigation engineering. It represents the volume of water flowing per second.

3. Hectares/cumec: This unit represents the ratio of the area of land being irrigated to the volume of water required per second. It indicates how much land can be irrigated with a given flow rate of water.

- High duty: When the duty is high, it means that a relatively small area of land can be irrigated with a given flow rate of water. This implies that the water requirement per unit area is low, and the irrigation system can cover a larger area.

- Low duty: Conversely, when the duty is low, it means that a larger area of land requires a higher flow rate of water for irrigation. This indicates that the water requirement per unit area is high, and the irrigation system can cover a smaller area.

In summary, the units hectares/cumec are used to define high and low duty in irrigation. High duty means a smaller area of land can be irrigated with a given flow rate, while low duty means a larger area requires a higher flow rate for irrigation. These units help in designing efficient irrigation systems and ensuring adequate water supply for crops.