Comparison of Penman-Monteith and Priestley-Taylor Evapotranspiration Methods for Crop Modeling in Oklahoma

Potential evapotranspiration (PET) is a key variable simulated by most crop simulation models using a variety of approaches. The objective of this study was to compare Priestley-Taylor (PT) and FAO-56 Penman-Monteith (FAO-56 PM) PET methods when simulating crop evapotranspiration (ET), yield, and aboveground biomass in Oklahoma. The study used data from 87 weather stations across nine climate divisions to simulate maize, sorghum, soybean, and wheat crop growth and development in Oklahoma for 1998 to 2017. Our results show that seasonal crop ET estimated by PT was lower than FAO-56 PM in most climate divisions and crops with average difference ranging from -10 to -1% for rainfed and from -21 to -1% for irrigated simulations. Differences in ET were greater for winter wheat than for maize, sorghum, and soybean. Additionally, differences in ET between methods were smaller in humid regions than in arid regions. Analysis of simulated rainfed yield and biomass showed higher values with PT for all crops except in the most humid climate divisions. However, under full irrigation, the yield differences between PT and FAO-56 PM were very low and ranged between 0-2% for all crops. In conclusion, this study confirmed that PT estimation of ET could be significantly different from FAO-56 PM especially in the arid and semiarid regions and during the winter under rainfed conditions. However, the differences in ET estimation did not affect yield and biomass simulation under full irrigation because the impact of soil water balance on the crop growth simulation was removed.