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THE POPULAR SCIENCE MONTHLY.
It follows that the prevention of surface evaporation, to the utmost extent possible, is of the first importance.
Now, the simplest, cheapest, and most universally practicable mode of diminishing evaporation from a bare land surface is to
![](http://upload.wikimedia.org/wikipedia/commons/thumb/a/a7/PSM_V48_D682_Alkali_salt_content_chart_of_irrigated_land.jpg/500px-PSM_V48_D682_Alkali_salt_content_chart_of_irrigated_land.jpg)
keep it constantly in loose, fine tilth, to a depth which varies with soil and climate. In humid climates four inches has been found