Variation of Priestley-Taylor Model Parameter in Rain Fed Spring Maize Field

The study on Priestley-Taylor (PT) reference crop evapotranspiration model coefficient (α) in local area is of great significance in semi-arid agricultural water resources efficient use and precision irrigation in corn. Here, based on the FAO (1998)-recommended Penman-Monteith (PM) reference crop evapotranspiration as a standard method, we determined the water and heat exchange and its estimated parameters by the eddy covariance technique and Priestley-Taylor model under local climatic conditions. The results indicated that the estimated values of reference crop evapotranspiration (ET 0-PT 1.26 ) gained from PT model-recommended coefficient (α = 1.26) lowed by 21.2% on an average during non-growth stages (from November to April next year), and reached an average of 5.5% higher than those from PM model reference crop evapotranspiration (ET 0-PM ) from May to September. The local PT model coefficient α value was 1.15 ± 0.06. The average PT model coefficient at noon during growth stages showed a single peak changing trend with the highest value of 0.67 ± 0.08 from tasseling to flowering stage and with the lowest value of 0.26 ± 0.13 at seedling stage. In conclusion, if the reference crop evapotranspiration is necissery to be estimated accurately by PT model in the semiarid climate area, the local PT parameters should be studied firstly.