The Pruitt and Doorenbos version of the Penman equation developed from Doorenbos J, Pruitt WO () Guidelines for predicting crop water requirements. Doorenbos, J. and W.O. Pruitt. Crop water requirements. FAO Irrigation and Drainage Paper No. Food and Agric. Organiz. of the U.N. Rome. Fereres. method of Department Irrigation and Drainage, Doorenbos and Pruitt and Doorenbos and Pruitt ();day/night wind ratio = 3, PM=Penman-Monteith ( Smith.

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The values of Kp were calculated by the relationship between ETo, from the lysimeter, and ECA, and estimated from the following methods: Table 2 presents the statistical analysis of ETo estimates using different Kp methods.

The original Brunt model and FAO model for wet climates performed more poorly than did the other models in estimating the Rn and ET0. Revista Brasileira de Agrometeorologia, Santa Maria, v. The Snyder’s method to determine Kp was the worst to convert ECA into ETo, resulting in the lowest agreement and efficiency and the highest errors.

In addition to the sensor readings Rnmeasuredfive different models were used in order to obtain the Rnestimated. Operational estimates of reference evapotranspiration. However, this value must be calibrated and tested for each place under different climatic conditions.

According to Pereira et al. The use of an arbitrary and constant Kp 0.


It can be seen that Kp predicted by all methods remained between 0. The same routine was adopted to evaluate ETo estimates with the different Kp values. A model for the class A pan coefficient.

Scientific Research An Academic Publisher. Journal of Geophysical Research, Ottawa, v. The grass was clipped whenever necessary to keep its height between 0.

There are several methods to determine Kp values, using wind speed, relative humidity and fetch length and conditions. Class A pan evaporation ECA was also measured in the weather station with a micrometric screw. Services on Demand Journal.

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Agricultural and Forest Meteorology, Amsterdam, v. Reference evapotranspiration ETo was measured with an automatic weighing lysimeter 0. The class A pan coefficient Kp has been roorenbos to convert pan evaporation ECA to grass-reference evapotranspiration EToan important component in water management of irrigated crops. The Rnestimated obtained with the fifth model has a relatively high error.

Report on expert consultation on procedures for revision doorenhos FAO methodologies for crop water requirements.

Evapotranspiration as a function of leaf area index and class A pan evaporation. Converting from pan evaporation to evapotranspiration. Four of those models consider the effects of cloud cover: Then, Snyder presented another equation to predict Kp using the same variables in a multiple linear regression.

Agronomy Journal, Madison, v.

This fixed value is a practical and simple option to convert ECA into Doorebnos, but this value must be calibrated for each place under different climatic conditions. We used meteorological data collected between August and Juneon a daily basis and on a seasonal basis wet vs.


Class A pan coefficients (Kp) to estimate daily reference evapotranspiration (ETo)

This paper analyses the following methods to estimate Kp values: The best Kp methods to estimate ETo were Pereira et al. The fifth was a linear regression model based on Rs. The atmospheric pressure was determined by aneroid barograph, and sunshine duration was quantified with a Campbell-Stokes recorder.

Equation for evaporation pan to evapotranspiration conversion. Class A pan coefficients Kp to estimate daily reference evapotranspiration ETo. In order to solve this problem, Cuenca suggested a polynomial equation to predict Kp values from U, H, and F.

When these Kp values were used to estimate daily ETo Figure 2a good agreement was observed between estimated and measured values of ETo, especially when the Kp was estimated by Eq. When a constant value of Kp 0.