Determination of crop coefficient has potential advantage for proper irrigation scheduling. This research was carried out to determine the single crop coefficient (Kc), basal crop coefficient (Kcb) and the ratio of transpiration to evapotranspiration of canola ((Brassica napus L.) based on lysimetric data in Research Farms of the Tabriz University, Iran. Relationships of the crop coefficients Kc or Kcb, and the parameters of days after planting (DAP), degree-growing days (GDD), leaf area index (LAI), ground cover percentage (GC %) and the ratio of transpiration to evapotranspiration (T/ET) with LAI and GC% were analyzed. The values of seasonal crop ET were 582 and 550 mm in the years of 2010 and 2011, respectively. The seasonal transpiration was calculated 467 and 410 for canola in the first and second years, respectively. The average, maximum, and minimum values of Kc were 1.03, 1.47 and 0.57 and of Kcb were 0.76, 1.37 and 0.0 in 2010; also these values in 2011 were 0.90, 1.24 and 0.41 for Kc and 0.64, 1.06 and 0.0 for Kcb, respectively. The value of T/ET ratio was 0.0 at the planting date and increased to 0.80 and 0.87 during the growth season in 2010 and 2011, respectively. The value of T/ET increased rapidly when LAI values were smaller than 3.0 and 2.5 in both experimental years. Finally, results obtained from the study can be used as reference data for irrigation scheduling and soil water modeling of canola.
