EFFECT OF FALL IRRIGATION" ON CROP YIELDS. 13 
There were no significant differences between the average yields 
secured on the fall-irrigated plats and those on the check plats. 
Soil-moisture determinations were made in the spring and early 
summer each year. In 1914 they disclosed no significant differ- 
ences in the moisture content of the soil resulting from fall irriga- 
tion except that in the first two of the three samplings more moisture 
was found in the first 3 feet of the fall-irrigated plats than in the cor- 
responding depths of the check plats. No effect was noted beyond 
the third foot. The difference found in the upper 3 feet existed 
at a time when all the plats contained abundant moisture, and it 
disappeared before the end of June. No significant differences were 
found in 1915 or 1916. 
The failure of fall irrigation to increase crop yields in these ex- 
periments seems to be attributable to the character of the soil at 
Belle Fourche. This soil is a heavy clay, which will absorb water 
only when dry and which expands rapidly when moisture is added 
to it. This expansion so compacts the soil as to make it imper- 
vious, so that the storage of water in the lower depths for the use of 
crops is not practicable. 
