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Water Balance Study of Tonle Bati Irrigation Project, Cambodia
Thesis Abstract:
This study on water balance in the paddy field was done to determine crop evapotranspiration and water use efficiency. The experiment was conducted during the main season for three rice varieties, namely: Phcar Khney, Kung Sor, and IR 66. All varieties were nursed and transplanted in three adjacent plots. Three plots, 100 m2 each, were prepared in a large paddy field. The transplanting spacing in the experimental plot was 20 x 20 cm and the number of seedlings per hill was three. The results obtained on seasonal water requirement for evapotranspiration varied with varieties. They were 680, 771, and 454 mm for Phcar Khney, Kung Sor, and IR 66, respectively. Daily average evapotranspiration was 6.1 mm/day throughout the season for all varieties.
Water use efficiency was calculated by using the equation (Etc + S&P)/(IR + RF). The results obtained ranged from 50 to 71 percent or an average of 63 percent for the three plots. For an area where lateral seepage is negligible, the water use efficiency should be 60 percent for wet season rice.
The cumulative seepage and percolation were -59, 156, and 232 mm for 1st, 2nd, and 3rd plot, respectively. Daily average percolation was about 1 mm/day throughout the wet season. Water depth of 368-484 mm was recorded as supplementary irrigation water requirement at the early part of the season. Drainage water ranged from 282 to 753 mm based on the difference in duration of rice growing periods.
In addition, pan evaporation and effective rainfall were also recorded and calculated. Daily average evaporation was 4.15 mm/day, and for the effective rainfall it was about 55 percent throughout the wet season.