ARS | Publication request: MEASURED AND MODELED PLANT AND SOIL WATER EVAPORATION OF COTTON

Submitted to: Agronomy Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: October 21, 2001
Publication Date: October 21, 2001

Technical Abstract: Modeling transpiration (T, mm) and soil water evaporation (E, mm) separately often improves the prediction of evapotranspiration (ET, mm). The FAO-56 methodology for the prediction of crop water use uses dual crop coefficients for separate calculations of T and E. We measured ET of irrigated cotton (Gossypium hirsutum L.) at full vegetative cover that was grown in a weighing lysimeter containing Amarillo sandy loam (fine-loamy, mixed thermic Aridic Paleustalf). Concurrent measurements of T were made using heat balance sap flow gauges on all cotton plants growing on the lysimeter to determine E as a residual of the measured components, or E=ET-T. Daily ET modeled by the dual crop coefficient methodology was compared with measured ET determined by mass change of the lysimeter, as well as modeled to residually determined E. For the 22-day measurement period, total measured ET was 173 mm and modeled ET was 168 mm. Residually ydetermined E was 18 mm and modeled E was 26 mm. Errors in modeling E were due to the tendency of the FA0-56 methodology to overestimate E following an irrigation, but overall the dual crop coefficient methodology in FAO-56 modeled both E and ET adequately.