Consumptive use (evapotranspiration) of water by a crop: Which statements correctly describe consumptive use for irrigation planning?

Introduction / Context:
Consumptive use (evapotranspiration) is the total water used by the crop for transpiration and soil evaporation. It is core to water requirement estimation and canal capacity planning in irrigation engineering.

Given Data / Assumptions:

• Agronomic and hydrologic perspectives are both acceptable.
• We consider units and sources of supply.

Concept / Approach:
Consumptive use can be communicated either as a depth (mm or cm) over a field or as a volume per unit area (m^3/ha). Effective rainfall contributes to consumptive use, reducing irrigation demand; the balance is provided by irrigation application and possibly stored soil moisture.

Step-by-Step Solution:
Recognize that ET can be represented in multiple equivalent forms (depth or volume/area).Acknowledge that rainfall offsets part of the irrigation requirement.Thus, all listed descriptions are correct.

Verification / Alternative check:
Water balance methods (e.g., FAO-56) compute ET as a depth, then convert to volumes by multiplying by area; effective rainfall explicitly enters the balance.

Why Other Options Are Wrong:
Each individual statement is correct; therefore the combined option “All the above” is the best.

Common Pitfalls:

• Confusing gross irrigation depth with consumptive use; gross depth includes application and conveyance losses.
• Ignoring effective rainfall, leading to overestimation of required canal discharge.

Final Answer:
All the above