Influence of Advection on Energy Balance in Canola Crop Evapotranspiration Process in Tabriz Region

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An experiment to study the effect of advection on energy balance in process of canola field evapotranspiration was designed and conducted at the Agricultural Research Station of Tabriz University in spring of 2010. For this research canola was planted in a lysimeter located in the middle of a 1.6 hectare experimental field. Evapotranspiration rate, leaf area index and plant height were determined inside the lysimeter. The advection phenomenon was investigated using the energy balance in the field surface, Priestley-Taylor coefficient  and the ratio of evapotranspiration obtained from advection energy to vegetation surface evapotranspiration . Bowen’s ratio (β), and ratio of lysimetric evapotranspiration to received net radiation in the fields  on different days after planting in the canola field were also determined. Negative values of sensible heat flux confirmed the  advection occurrence from 39 days after planting and values of  and  showed that advection affected evapotranspiration process as significantly in this region. The values of  reached more than 60 percent in some days of the growing season. This issue clearly proved the influence of advection energy on canola field evapotranspiration. In the study region except regional advection, local advection could occur across large fields due to the existance of small farms, different timings and amounts of irrigation and fallow duration of some farms. Results showed that, when leaf area index and plant height reached to 1 and 15 cm respectively, temperature gradient between the farm and the surrounding area were increased due to increment of LAI and plant height which increased the transpiration in turn. In this stage the resulted negative values of β and H confirmed the occurance of advection phenomenon

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