ABSTRACT
Abstract This paper presents the principle and methods of computerizing irrigation scheduling of cotton fields in the Jianghan Plain of China where the groundwater table is shallow. According to the changing patterns of daily reference evapotranspiration (ETo) estimated from the modified Penman Equation, models for forecasting daily ETo are introduced. Based on the experimental data from the Tianmen Irrigation and Drainage Experiment Station (TIDES) for many years, the methods for calculating crop coefficient and water stress coefficient are discussed. Another feature of the model concerns the accounting for the contribution from groundwater to the root zone of cotton. An empirical equation for estimating the capillary rise from groundwater table is suggested in line with the measured data. The computer program is compiled in Lotus 123 worksheets and is available as a menu-driven package. The application shows that the principle and mathematic models introduced in the paper are feasible and simple to use. Keywords: Cotton, evapotranspiration, groundwater, irrigation scheduling, modeling, realtime.
