Bare-soil evaporation determined in situ by infrared thermometry

Bare-soil evaporation was measured in situ by infrared thermometry. Measurements were made at 25 sites on a 20 × 20-m plot. About 17 mm of water were added during the first test in March 1982 and 27 mm during a second experiment in May, both in a rainless and sunny period. The method requires measurement of wind speed, the maximum surface temperature of the test soil and a reference dry surface. Measured values of the evaporation were well correlated (r² = 0.7) with water added, and the amount of evaporation measured for a 1-week period was of the same order of magnitude as the added water. Supporting information of surface water content by gravimetric and neutron measurements helped to complete water-balance calculations on each site. The method is proposed as a tool for evaluating spatial variability for water-balance studies in large areas. Semi-variograms were prepared for evaporation on the site and fitted by assuming a linear drift.