What term refers to the basic measurement of irrigation water use?

The term "acre-inch" is indeed recognized as the basic measurement of irrigation water use. It quantifies the volume of water required to irrigate one acre of land to a depth of one inch. This measurement is particularly important in agriculture, as it helps farmers and agronomists determine how much water is needed for effective irrigation practices, allowing them to manage their water resources efficiently. Knowing the acre-inch can aid in calculating total water requirements for crops, scheduling irrigation events, and ensuring optimal growth conditions.

In contrast, while other options like water depth and water usage rate are related to measuring water, they do not capture the entirety of irrigation water use as clearly as the acre-inch. Water depth alone measures how deep the water sits after application, without providing a volume metric over an area. The water usage rate refers to the speed at which water is consumed or applied, which can vary and may not directly reflect total water use over a defined area. Irrigation efficiency relates to how effectively water is applied and utilized by the plants, but it too does not encapsulate the basic measurement of water use in the same unequivocal manner as an acre-inch does.