The technical term used to relate the volume of water and the area of crop it matures is
Show Hint
Important irrigation terms:
\[
\boxed{
\begin{aligned}
\text{Duty} &\rightarrow \text{Area irrigated per unit discharge}\\
\Delta &\rightarrow \text{Total depth of water required}
\end{aligned}
}
\]
Step 1: Recall the definition of duty of water.
Duty is the area of land that can be irrigated by a unit discharge of water flowing continuously during the crop's base period.
Step 2: Identify the correct term.
Thus, the quantity relating the volume (or discharge) of irrigation water to the area of crop matured is called
\[
\boxed{\text{Duty}.}
\]
Hence,
\[
\boxed{(A)}
\]
is the correct answer.