REAL-TIME FORECASTING OF IRRIGATION WATER REQUIREMENTS OF PADDY FIELDS

This paper presents the principle and methods of computerising irrigat ion scheduling of paddy fields under intermittent submerged conditions . Models for forecasting daily evapotranspiration of rice are discusse d, Under intermittent submerged conditions, there is no ponded water l ayer for most days after the rice turns green, so slight water stress occurs occasionally, The physiological mechanism and ecological charac teristics of rice under limited water supply are quite different from those under submerged conditions; therefore, in estimating the evapotr anspiration of rice, both lag and overshoot are considered in the mode l. Another feature of the model concerns the accounting for the contri bution from the slow drainage of mobile water after the disappearance of the water layer in the paddy field. The model is compiled in Lotus 123 worksheets and is available as a menu-driven package.