Estimation of Actual Evapotranspiration and Crop Coefficient of Transplanted Puddled Rice Using a Modified Non-Weighing

Abstract

A lysimeter and eddy covariance can be used to estimate actual evapotranspiration (AETc,) directly. However, these technologies are costly, making in-situ ET determination difficult, particularly in developing countries. In view of this, an attempt was made to determine AETc, and stage-wise crop coefficients (Kc) of transplanted puddled rice using a modified non-weighing paddy lysimeter. The results were compared to indirect methods using FAO Penman-Monteith and Pan Evaporation. Daily AETc, ranged from 1.9 to 8.2 mm/day, with a mean of 4.02? 1.35 mm/day, and their com-parison showed that the FAO Penman-Monteith equation performed well (R2:0.63; MSE: 0.64; RMSE: 0.80) and was highly correlated with AETc, throughout the crop season. However, the Pan evaporation approach was underestimated (R2=0.24; MSE=0.96; RMSE=0.98) due to a consistent pan coefficient (0.71), vegetation role and human error. In addition, Actual Kc values were de-termined to be 1.13, 1.27, 1.23, and 0.93, respectively, for the initial, crop development, mid-season and end season, higher than FAO Kc. Statistical analysis results revealed that the overall stage-wise derived Kc was in line with FAO values (R2= 0.97; p= 0.45) but different from derived pan Kc values (R2= 0.93; p= 0.33), although insignificant at 5% significance level. Therefore, such a methodology should be used without lysimeter availability. The derived regional Kc values may be utilized for precise irrigation scheduling to enhance paddy water productivity in similar agro-climatic regions worldwide.