Under the humid-temperate climatic conditions of Illinois, the high Na content of natric horizons can be reduced and corn yields on natric soils can be increased greatly by mixing high rates of gypsum with the soil to a depth of 90 cm and installing tile at the 90-cm depth with no more than about 9 or 10 m spacing to carry the sodium out of the profile in drainage water. From the results obtained with the treatment in this article, it is estimated that about 13 to

15 years are needed to remove enough of the extractable Na from the Huey profile to a depth of 90 cm to reduce it to noninjurious levels.

Mixing gypsum only in the plow layer had no effect with or without tile, probably because the gypsum was not effectively moved downward into the very slowly permeable natric horizon. Chiseling gypsum to a depth of 60 cm at 60 cm intervals in two directions increased corn yields slightly but not significantly over check plots.

Mixing the natric horizon with the total soil to the 90-cm depth without gypsum resulted in reduced corn yields, very poor soil physical condition in the plow layer, and intensified naturally severe drainage problems.

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