16 BULLETIN 133, U. S. DEPARTMENT OF AGRICULTURE. 



land than on the land that was not fall irrigated. The difference was 

 about 7 per cent on March 30 and May 15, about 3 per cent on May 28, 

 more than 8 per cent on June 13, 4 per cent on June 27, 1 per cent on 

 July 10, and 4 per cent on September 28. That these differences in 

 the average moisture content of the first 6 feet were due mainly to the 

 relative dryness of the lower portion of the 6-foot zone of soil on the 

 land not fall irrigated can be seen by an examination of figures 3, 4, 

 and 5. 



Figure 3 shows the average moisture content of the first 3 feet on 

 the two series. It is seen that the fall-irrigated land had more mois- 

 ture in the upper 3 feet of soil than the land not fall irrigated, but the 

 differences were decidedly less than those obtained where the upper 6 

 feet were considered, except on March 30, when the difference was 

 nearly as great as that shown in figure 2. 



As shown in figure 4, the moisture content of the upper foot of soil 

 was very nearly the same on both series throughout the season, but 

 the fall-irrigated land contained somewhat more moisture on all the 

 sampling dates except July 10. 



Figure 5 shows the moisture content of the sixth foot of soil during 

 the season of 1911. It is seen that the sixth foot of soil on the land 

 not fall irrigated was comparatively dry throughout the season. It 

 contained about 5 per cent of moisture on March 30, and tins moisture 

 content increased to about 9 per cent by September 28. The sixth 

 foot of soil on the fall-irrigated land contained nearly 12 per cent of 

 moisture on March 30, and about the same on September 28. 



A study of these four figures leads to the following conclusions: 

 (1) The irrigation water applied in the fall supplied abundant moisture 

 to the soil to a depth of at least 6 feet, while the land not fall irrigated 

 remained relatively dry during the following winter. (2) The irriga- 

 tion water applied during the season of 1911 percolated to the lower 

 depths in the moist soil of the fall irrigated land more rapidly than in 

 the relatively dry soil of the land not fall-irrigated. (3) The more 

 favorable soil-moisture conditions on the fall irrigated land during 

 the growing season were due chiefly to the fact that on that land the 

 soil was well supplied with moisture at the beginning of the season. 



SUMMARY. 



(1) In many sections of the Great Plains area a comparatively 

 small proportion of the annual precipitation comes during the period 

 from October to March, inclusive, and the result is that the soil is fre- 

 quently too dry at planting time in the spring to promote germina- 

 tion and support an early growth of spring-planted crops. 



(2) Experiments were started in the fall of 1910 at the Scottsbluff 

 Experiment Farm to determine whether fall irrigation of the land 

 would improve the soil-moisture conditions and result in better yields 

 of field crops. 



