Evapotranspiration estimates from heat‐budget measurements over a field crop

The heat‐transfer processes which occur at the Earth's surface have direct bearing on many of the physical problems in agriculture that relate to the plant environment. The evapotranspiration from a crop can be estimated from the disposition of solar and sensible energy available at the earth‐air interface. A suitable measurement of the heat budget, including net radiation, heat transfer by soil conduction, air‐temperature gradient above the crop, and vapor pressure gradient above the crop, will account for the fraction of solar energy used hourly or daily for evapotranspiration. The simple theory, a brief description of the experimental equipment, and some illustrative measurements are discussed.