Internal drainage under irrigation of two slowly permeable subsoils of the northern Great Plains.
Trooien T.P. | Reichman G.A.
Lack of water limits crop yield in the semiarid northern Great Plains but many soils of the northern Great Plains have been thought to be nonirrigable because of their slowly permeable subsoils. We measured the internal drainage in response to two levels of nitrogen fertility and three levels of irrigation or overirrigation--one, two, or three times the calculated evapotranspiration--of corn (Zea mays L.) at two sites for five and six years. Both of our sites had subsoils classified as slowly permeable; one site had alluvial subsoil, the other had glacial till subsoil. For sufficient nitrogen fertility (200 kg N/ha) at the glacial till site, drainage between 1 July and harvest from the 2ET treatment was 109 mm greater than from the 1 ET treatment; drainage from the 3ET treatment was 197 mm greater than from the 2ET treatment. Insufficient nitrogen fertility (100 kg N/ha) reduced crop water use and resulted in greater drainage. At the glacial till site, the average internal drainage between 1 July and harvest from all three irrigation treatments at 100 kg N/ha was 100 mm greater than at 200 kg N/ha. The maximum five-year average drainage amount between 1 July and harvest at the till site was 471 mm, more water than the average applied to the 1ET treatments during the same period. Tensiometer measurements occasionally indicated saturation at the 2.0-m depth at the alluvial site, but not at 0.9 or 1.35 m; saturation was never encountered at the till site at 0.9, 1.35, or 2.0 m. Based on the measured drainage rates and lack of perched water table development, the soils tested in this study can drain enough water to permit successful well-managed irrigation.
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