What is "lysimeter"

Lysimeter \Ly*sim"e*ter\ (l[-i]*s[i^]m"[-e]*t[~e]r), n. [Gr. ly`sis a loosing + -meter.] An instrument for measuring the water that percolates through a certain depth of soil.
--Knight.

n. an instrument that measures the percolation of water through soil

A lysimeter (from Greek λύσις (loosening) and the suffix -meter) is a measuring device which can be used to measure the amount of actual evapotranspiration which is released by plants (usually crops or trees). By recording the amount of precipitation that an area receives and the amount lost through the soil, the amount of water lost to evapotranspiration can be calculated. Lysimeters are of two types: weighing and non-weighing.