Date of Award:


Document Type:


Degree Name:

Doctor of Philosophy (PhD)


Plants, Soils, and Climate

Department name when degree awarded

Soil Science and Biometeorology

Committee Chair(s)

R. J. Hanks


R. J. Hanks


L. G. King


J. E. Christiansen


H. H. Wiebe


D. W. James


A mathematical model was developed to predict water content profiles, evapotranspiration, water flow from or to the water table, root extraction and root water potential at the surface as functions of time under unsteady state conditions.

The model was tested in the field at The Hullinger Farm near Vernal, Utah, in 1970 and 1971. Comparison of water content-depth profiles show excellent agreement at the end of a 9- day run in 1970 on oats seeded to alfalfa. In 1971 with alfalfa as the crop, the data show best agreement, between predicted and computed water content-depth profiles, 48 hours after any water addition. The poorest agreement for both crops was right after irrigation.

The computed cumulative ET was 4.9 em which was 0.4 em less than actual (measured) ET, during the 9- day period in 1970. In 1971, the actual and measured ET were the same for the whole season. This agreement may be partially due to the "forcing" of the water removal by ET to be the same as measured.

In 1970, the computed cumulative upward flow from the water table was 2.20 em which was 0.1 em greater than the actual for the 9-day period. In 1971, the cumulative upward water flow from the water table was 4.80 em which was 3.20 em greater than the calculated for the whole season of 116 days.