Evaluation Of Evapotranspiration Methodsand Development Of Crop Coefficient For Maize And Wheat In Yangling

Knowledge of crop water requirement is an important practical consideration to improve water use efficiency in irrigated agriculture.Rotational crop of winter wheat and summer maize using Gravimetric lysimeter is practice large scale in arid region of North-western China.It is necessary to find a simpler method in different climatic regions to calculate reference crop evapotranspiration(ETo)since the application of the FAO-56 Penman-Monteith method is often restricted due to the unavailability of a comprehensive weather dataset.In this study,five of the most commonly used reference ET methods were applied to assess the relationship between them.The FAO56-Penman Monteith(FAO56 PM),Penman Monteith(PM),Priestley Taylor(PT),Hargreaves(HG)and Makkink(MK)methods were used to predict ETo,with the aim of predicting the amount of reference evaporation for this purpose.The FAO-PM and PM methods necessarily require meteorological data to process their ETo calculations,while MK and PT require some of them for estimation.Therefore,in this study,the five were compared and their importance was statistically analyzed and recommended for use in semi-arid environments.The aim of the study was to evaluate the most reliable ETo estimation models and crop coefficients for winter and summer maize crops to estimate the water requirements of wheat in a semi-arid environment.Determining the priority of the ETo estimation method based on its performance,especially for semi-arid areas with high evaporation requirements,will enable users to choose the next best alternative with limited weather data availability.In this study,a field experiment was carried out during 2013-2017 growing season to examine water used and the correlation between ET measurement and ET estimations with its factor included temperature,solar radiation,relative humidity,and wind speed in an arid environment.Analysis of the standard scores of ET and meteorological variables showed that ET measurements and estimations by both methods highly depended on solar radiation and temperature,but were less related to relative humidity and wind speed.The Comparison was made between the FAO-56 Penman-Monteith and other four simple alternative methods,using the standard error of estimation(SSE)and the coefficient of determination R~2.This is directly related to accurate estimation of crop evapotrasnpiration(ETc)which depends on crop characteristics and development stage,weather parameters,environmental conditions,and management practices.The five reference ET methods(i.e.FAO-56 Penman–Monteith(FAO56PM),Penman-Monteith(PM),Priestly-Taylor(PT),Mankink(MK)and Hargreaves(HG)were evaluated for their capabilities to predict ETo using daily weather data.Statistical analysis showed that the Penman-Monteith(PM)may be instead of the FAO-56 Penman–Monteith method in predicting ETo value in this region.