12 BULLETIN 546, U. S. DEPARTMENT OF AGRICULTURE. 
dition of the soil near the surface. Alter the layer of easily pene- 
trated soil becomes wet, it becomes so swollen and compact that it 
is nearly impervious, and further water movement is very slow." 
The results secured in the fall-irrigation experiments at Belle 
Fourche are in accord with these observations. The application of 
irrigation water in the autumn filled the surface soil to its moisture- 
carrying capacity, but apparently had no effect beyond the third 
foot. Irrigation water applied uniformly to all plats during the 
growing season, together with the natural precipitation, equalized 
the moisture content of the soil in these plats, irrespective of their 
treatment the previous fall. It is important to note also that an 
abundance of moisture was present in all the plats at the time of 
sampling in the spring and early summer and that after this time 
moisture was supplied by irrigation. 
These facts account for the absence of significant differences be- 
tween the average yields of crops on the fall-irrigated plats and 
those secured on the check plats. It is possible that if an adequate 
supply of moisture had not been maintained by irrigation during 
the growing season the soil-moisture content of the fall-irrigated 
land would have been higher in the spring than that of the check 
plats. It seems certain, however, that where crops are properly 
irrigated during the growing season fall irrigation on this soil will 
have no material effect. 
SUMMARY. 
The fight precipitation received during the winter months in the 
Great Plains area commonly causes soil to remain dry from the time 
crops are harvested until the rainy season the following year. In 
some soils this deficiency of moisture may have an unfavorable in- 
fluence on the growth of crops, both by hindering the germination 
of spring-sown seed and by retarding or preventing the desired 
movement of the water received as precipitation or applied in irri- 
gation during the growing season. 
Fall irrigation has been advocated as a corrective of this condi- 
tion in irrigated regions. It has been found efficacious on sandy 
loam soil in western Nebraska, where it resulted in increased soil 
moisture in the spring and in greater moisture absorption by the 
soil throughout the irrigation season. 
In order to test the practice of fall irrigation on a heav}^ clay soil, 
experiments were conducted at the Belle Fourche Experiment 
Farm, in western South Dakota, in 1914, 1915, and 1916. These 
experiments included wheat, oats, barley, flax, potatoes, sugar 
beets, and corn, each crop being grown each year in duplicate tenth- 
acre plats both on fall-irrigated land and on land which received no 
fall irrigation. 
