Date of Award:

1976

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Plants, Soils, and Climate

Advisor/Chair:

R. J. Hanks

Abstract

An estimate of potential evapotranspiration is acquired to implement an irrigation scheduling program. Four equations, which estimate potential evapotranspiration (evaporation) were evaluated for prediction of Class "A" Pan evaporation. The equations used were Penman's combination equation, the Jensen-Haise temperature and radiation equation, and two of the Christiansen-Hargreaves polynomial regression type equations. Measured and calculated radiation was used together with two values of albedo. Four years of daily climate data from Rhodesia was evaluated by general linear regression methods.

Despite the significant variations between the four annual regression lines of each equation, the use of confidence intervals indicate that the Penman and Christiansen-Hargreaves equation adequately predict Class "A" pan evaporation for irrigation control purposes.

Using class "A" pan evaporation as the measure of potential evapotranspiration for sugarcane, a computerized irrigation scheduling model was developed.

Controlled plant moisture stress was incorporated in the program with an irrigation coefficient related to the limiting effects of low soil moisture on plant transpiration. Five soil moisture regimes and two levels of irrigation were studied.

Within the limits of the defined soil moisture assumptions, the program exhibited considerable flexibility in computation and the control of desired plant moisture stress.

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