NORTHERN GREAT PLAINS FIELD STATION, 1913-1922 5 
tionallydry. These were the driest consecutive six years during the 48- 
year period. 
The 48-year average annual precipitation was 17.04 inches. The 
average annual precipitation for the 10-year period 1913-1922 was 
15.83 inches. This is the period during which the field station has 
been in operation. For the 8-year period 1915-1922, for which 
crop yields are presented, the average annual precipitation was 15.20 
inches. The quantity of precipitation during September, October, 
and November very often determines crop production in the following 
year. A very dry fall is usually followed by a season of low crop pro- 
duction; that is, if the soil goes into the winter dry the chances for 
good crops the following season are greatly reduced. 
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Fic. 1—Diagram showing the annual precipitation at Bismarck and Mandan, N. Dak., for the 48-year 
period from 1875 to 1922, inclusive. The solid line indicates the average for the whole period. The broken 
line indicates the average for nine years at Mandan 
SOIL ° 
~The soil on the Mandan tract varies considerably, especially in 
texture. That on the plateau above the terrace on which the field- 
station buildings stand is a loam, the sand constituent being fine to 
very fine. On the experimental plats the soil is sandy loam. The 
experimental plats around the station buildings are located on a 
bench, consisting of a terrace, but the texture of the substratum is 
not light enough to affect the moisture relations in the soil horizons. 
The normal mature soil of the region has a profile in which the 
illuvial horizon universally characteristic of the subsoil in humid 
regions is absent. The subsoil has about the same texture as the 
soil except in those spots where the texture of the former horizon is 
determined by geological factors rather than the processes of soil 
development. This latter condition would apply only to the soils 
on the terraces and not those on the uplands. 
3 This brief description and analysis of the soil was furnished by C. F. Marbut, in charge of Soil-Survey 
Investigations, Bureau of Soils 
