Fraction of Net Radiation Utilized in Evapotranspiration from a Corn Crop

Graham, W. G.; King, K. M.

Fraction of Net Radiation Utilized in Evapotranspiration from a Corn Crop

1961

Graham, W. G. | King, K. M.

The ratio of daily evapotranspiration to net radiation was determined at various stages in the development of a corn crop. Measurements, made near the center of a 266- by 340-foot corn plot near Guelph, Ontario are reported for 16 days of observation during the summer of 1958. Soil moisture in the plot was maintained at a level exceeding 75% available. There was good agreement between the daily evapotranspiration determined by a floating lysimeter and the daily evapotranspiration computed hourly from the vertical heat budget method. The ratio of evapotranspiration to net radiation (E/Rₙ) averaged 0.81 ± .09 for the daytime period on days following rain when a large area was equally moist. Low values of E/Rₙ were associated with days of heavy cloud and high humidity. Values of E/Rₙ greater than unity during the daytime were obtained on some days when the corn plot was irrigated and the surroundings were dry. Freezing of the crop reduced E/Rₙ to 0.52. The stage of crop development prior to freezing did not have any effect on E/Rₙ under the soil moisture conditions of this experiment.

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