U. S. DEPARTMENT OF AGRICULTURE 
rains, of which a large proportion is stored in the soil. A larger per- 
centage of the average precipitation is lost in the Plains region owing 
to the larger amount of evaporation in the summer than in the 
mountains west. 
During the seven years of these experiments there were many crop 
failures in the northern Great Plains. These failures were not only 
on land that was cropped each year but also On land that was fal- 
lowed the previous year. The history of these fallow fields shows 
that the methods of managing fallow have varied greatly, no definite 
plan being generally followed in this region. 
SOIL ON WHICH THE EXPERIMENTS WERE MADE 
The soil on which the experiments were conducted is unirrigated 
bench land with an altitude of approximately 2,600 feet and is 
representative in general of that portion of central northern Montana 
having an altitude of 2,000 to 3,000 feet. 
This soil is classed as sandy clay loam and is of glacial origin. 
While it has a tendency to puddle when wet it does not crack when 
dry, as do the heavier soils. In the native state this soil is very 
compact and requires more than the usual power for breaking sod. 
It becomes rather impervious to moisture when the surface is too 
finely cultivated, but when not too fine it absorbs water readily. 
To the depth of 4 feet it will retain when fallow about 16 per cent of 
its dry weight of water, about half of which is available to wheat. 
This means approximately 5 inches of water. 
CLIMATIC DATA 
PRECIPITATION 
The precipitation for each of the 5 months from April to August, 
the total precipitation for that period, and the annual precipitation 
for each of the 7 years from 1917 to 1923, inclusive, are shown in 
Table 1. The precipitation during the 7 years under study was 
below normal. The average precipitation for the 44 years from 
1880 to 1923, inclusive, was 13.33 inches, but for the 7 years it was 
only 11.26 inches. The 44-year normal for the 5 months from April 
to August was 8.58 inches, whereas the average for these months 
for the 7-year period from 1917 to 1923, inclusive, was 7.17 inches. 
In each of the years 1917, 1918, and 1919 the total for the 5 months 
was less than 5 inches. In 1920, 1921, and 1922 the total was more 
nearly normal, and in 1923 it was 4.13 inches above the normal. 
The 7-year monthly averages were below the 44-year normals for all 
months except April, for which it was 0.03 inch above the normal. 
It is recognized that the distribution of precipitation during the 
growing season is an important factor in crop production. Yields of 
grain are strongly influenced by the amount and distribution of the 
June rainfall. In each of the 7 years under study except 1923 the 
precipitation in June was below the 44-year normal for that month. 
In 1922 the seasonal precipitation was about normal, but the June 
precipitation was much below normal, and the resulting injury to 
crops was severe. 
