Abstract
Water management of a subsurface-drainage and subirrigation system was simulated using a daily rainfall probability index ( rpi), to control the watertable depth ( wt) in the soil profile. Daily management of ‘free drainage’, controlled drainage, or subirrigation, was based upon the rpi value. The rpi was computed from the daily rainfall probability in forecasts issued by the U.S. National Weather Service. Climatic data and weather forecast records (1979–1985) for the lower Mississippi Valley were used in the DRAINMOD program to simulate daily fluctuations in the watertable. Various statistical and summation equations were used for computing the rpi. Management success was evaluated by conditions of excess and deficit soil water in the root zone, and by predicted crop yield. Using only the ‘today’ and ‘tonight’ segments of the morning (5:25 h) forecast, 75% of the significant rainfall events occurring during the growing season were successfully predicted when the rpi ≥ 0.60. Free drainage in advance of predicted storms significantly reduced the duration of excess soil water in the root zone and increased simulated maize yield 0 to 11%, when compared to controlled drainage where the water level at the drain outlet was maintained constant at a level above the drain.
Published Version
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