Difficulty: Easy
Correct Answer: Evapotranspiration and capillary potential
Explanation:
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:
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.
Step-by-Step Solution:
Identify lysimeter purpose: quantify field ET directly.Identify tensiometer purpose: measure capillary (matric) potential for irrigation control.Match the correct pair to the instruments named.Verification / Alternative check:
Compare with psychrometers or gypsum blocks; these measure related potentials but not ET directly like lysimeters.Why Other Options Are Wrong:
Permeability is measured via permeameters; velocities via hydrometric or velocimetric methods; vapour pressure is not directly measured by tensiometers.Common Pitfalls:
Confusing soil moisture content with potential; ET cannot be inferred from tensiometer alone.Final Answer:
Evapotranspiration and capillary potential
Discussion & Comments