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. 



