ISHS Acta Horticulturae 278: Symposium on Scheduling of Irrigation for Vegetable Crops under Field Condition
A SIMPLE EQUATION TO CALCULATE CROP EVAPOTRANSPIRATION: RESULTS OF SEVERAL YEARS OF EXPERIMENTATION |
| Authors: | N. Katerji, I. Ferreira, N. Mastrorilli, N. Losavio |
| Abstract:
In order to take direct measurements of crop evapotranspiration (ET), different methods can be used. However, these methods require high-tech supports. Usually, ET calculation is based on some coefficients which are determined statistically. In this paper, a simple formulation to estimate ET is presented. The formulation is suggested after the theoretical analysis of the expression for calculating ET and after the experimental verification of the relationship linking crop resistance measures to climatic factors. The proposed formulation is: ET = C [P'/ (P'+ where C is a parameter which has the same characteristics of a crop coefficient. For well-watered crops (corn, wheat, grass, alfalfa, potato, tomato) ET was measured in France, Portugal and Italy, by means of a weighing lysimeter or by the energy balance methods (Bowen ratio and simplified aerodynamic methods) along with the meteorological inputs required by the formula [1]. Values of coefficient C for actively growing crops are similar (1.2 to 1.4) in all investigated localities. From the results, it appears that the C term is capable of being modified by the crop's phenological stage and soil water content. The calculated C values in this trial were compared with those obtained by other authors in different crops and under quite different climate and soil conditions. The results of the comparison suggest that the C coefficient appears to be rather constant (C=1.3 on the average) if the soil water status is good and measurements are not affected by advective energy sources. | |
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