Design, Fabrication, and Operation of an In-Situ Microlysimeter for Estimating Soil Water Evaporation

Evapotranspiration (ET) or crop water use is the major consumptive use of irrigation and precipitation, commonly accounting for the largest component of the water balance. As water resources become scarce, agricultural research aims to increase water use efficiency by maintaining profitable crop yields while reducing ET. Advanced understanding of ET in the soil-plant-atmosphere continuum requires quantification of evaporation (E) and transpiration (T) components. However, the partitioning of E and T can be challenging even when using high quality ET data. Microlysimeters can be used to measure E from the soil surface and estimate T by subtraction using quality ET data. However, an understanding of the limitations of small, hydraulically isolated microlysimeters is required for meaningful interpretation of results. Proper design, fabrication, and operation of microlysimeters can yield reliable estimates of E from bare soil. Multiple microlysimeters and strategic placement may be required for accurate estimates of E in row crops, particularly during incomplete plant canopy conditions. Periodic weighing of lysimeter cores allows for time-averaged measurements of E but precludes E rate data at finer time scales. Design and testing of continuous weighing platforms to improve temporal density of microlysimeter measurements is needed. We present design and fabrication details of a compact, inexpensive, microlysimeter for field estimates of E in agricultural soils. Installation and operation techniques are also provided with discussion of example field data. Keywords: Evapotranspiration, Lysimetry, Microlysimeter, Soil evaporation.