Soil–water measurement devices: a lysimeter and a tensiometer are used to measure which quantities, respectively, in irrigation and soil physics practice?

Introduction / Context:
Efficient water management requires measuring both how much water crops consume and how strongly soil holds water. Two classic tools are the lysimeter, which quantifies evapotranspiration (ET), and the tensiometer, which gauges soil water tension (capillary potential) to aid irrigation scheduling.

Given Data / Assumptions:

• Lysimeter: a controlled soil–plant system with measured inflows/outflows to compute ET.
• Tensiometer: a porous cup connected to a vacuum gauge equilibrating with soil matric suction (low to moderate ranges).
• Focus is on routine agricultural engineering applications.

Concept / Approach:
Lysimeters determine ET by mass balance: ET = Inflows − Outflows ± Storage change. Tensiometers measure soil water potential (negative pressure relative to atmosphere) in the suction range where water columns can be maintained (typically up to ~80 kPa), indicating plant availability.

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