Evapotranspiration measurement and estimation using modified Priestley–Taylor model in an irrigated maize field with mulching

Accurate measurement or estimation of crop evapotranspiration (ET) is important to develop exact irrigation scheduling and reasonably use water resources. ET of an irrigated maize field mulched with plastic film was measured using eddy covariance technique over two growing seasons in an arid region of northwest China. A modified Priestley–Taylor (PT) model was developed, incorporating the effect of leaf area, soil moisture, mulching fraction and leaf senescence on ET. The model was parameterized by field measurements in 2008 and validated by those in 2009. Results indicate that diurnal variation of ET was bell-shaped curve for all the growing stages. During the two growing seasons, total ET was 503.1 and 562.4 mm, and mean daily ET 3.47 and 3.54 mm d−1, respectively. ET was mainly controlled by solar radiation, and significantly affected by influential factors below the thresholds, which were leaf area index of 3.0 m2 m−2, and soil relative extractable water of 0.5, and canopy conductance of 20 mm s−1, respectively. A good agreement was found between ET estimated by the modified PT model with observations, with linear slope of 0.99 and R2 of 0.94 and 0.96 for half-hourly and daily time scale, respectively. Thus the modified PT model can be used to estimate ET or quantify the effect of controlling factors on ET in similar agricultural fields.