Birara Gebeyhu*, Samuel Dagalo and Mekuanent Muluneh
Crop coefficients are very important to manage irrigation water throughout the irrigation period and that will depend on crop growth stage. In most irrigation practice, the recommended crop coefficients in food and agricultural organization irrigation and drainage paper manual used to fix crop water requirement. Therefore, this research was to develop crop coefficient model from growing degree days for wheat, maize, pepper and onion crops. To estimate crop coefficients, crop evapotranspiration was measured by using soil water balance Equation after measuring of soil water content before and after irrigation and reference evapotranspiration also observed from automatic climate station that install near the experimental area through the crop growth stage.
Total seasonal crop evapotranspiration and reference evapotranspiration of the wheat, maize, pepper and onion crops were 412.6 and 537.5 mm, 473.2 and 581 mm, 392.9 and 512 mm and 321.8 and 501 mm respectively. Polynomial degree four, three, five and three are the best fit Equation to predict crop coefficients from daily basis growth degree days with R2 are 0.93, 0.92, 0.96 and 0.94 for wheat, maize, pepper and onion crops respectively.
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