Abstract
Wheat was grown on a plot with an artificial slope of 10%, the difference between top and bottom being 2.5 m. The lowest part corresponded with the bottom of a drainage ditch. The watertable depth varied along the slope; it was always near zero at the bottom. Near the top, groundwater depth, although variable in summer, ranged around 1.5 m. Grain yield was affected by watertable depth and waterlogging duration. The maximum was reached at an average depth of 125 cm, and at deeper water levels it declined slightly due to shortage of water. When the average watertable depth throughout the season was 12 cm, the yield was only 25% of this maximum and it reached 82% at an average depth of 25 cm. When the SEW index was calculated with threshold values ranging from 0 to 80 cm, the yield response curves fell sharply above a critical value for SEW that depends on the threshold chosen. At slightly higher values total yield loss occurred. With low threshold values the response curves drop rapidly at first, and then flex; with high thresholds these curves initially remain horizontal and then bend gradually downward. The 40-cm threshold gives a practically linear response, from 100% to 66% of yield; thereafter yield collapses.
Published Version
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