SOIL AS WATER RESERVOIR 37 



the percentage of water in the soil in the fall. If the soil 

 went into the winter in a dry condition, practically all 

 of the winter precipitation was found in the spring in the 

 upper 8 feet. If, on the other hand, the soil was well 

 filled with water in the fall, from fallowing or fall irriga- 

 tion, a relatively small quantity of the winter precipita- 

 tion was found in the upper 8 feet of soil, when spring 

 opened. In both cases the soils were saturated in the 

 spring. That is, the upper foot was fully saturated; the 

 percentage diminished steadily with each succeeding 

 foot in accordance with the law of distribution already 

 explained. It was clear that when the soil was fairly 

 completely saturated in the fall, the winter precipitation 

 soaked down below the 8-foot limit. During six years, 

 1902 to 1907, the percentage of the total winter pre- 

 cipitation found stored in the soils that went into the 

 winter in the driest condition varied from 63 to 96 per 

 cent. 



This teaches, incidentally that, when the soil is sat- 

 urated to a depth of 10 to 12 feet, there is not an advan- 

 tage in adding more water. Therefore, in districts where 

 the precipitation comes in winter, early spring irrigations 

 may have little value. On the other hand, where the 

 winters are dry and the summers wet, early spring irriga- 

 tions should prove very profitable. 



At the North Platte substation of the Nebraska 

 Station, where the precipitation comes chiefly in early 

 summer, a similar series of experiments were conducted. 

 It was found that, in spite of the water-dissipating con- 

 ditions of summer, from 40 to 50 per cent of the rain 

 which fell from May 1 to September 1 was stored in the 

 soil to a depth of 6 feet at the end of the period. Since it 

 was evident that the water passed below the 6-foot limit, 



