CEREAL EXPERIMENTS AT THE WILLISTON SUBSTATION. 3 
PHYSICAL FACTORS. 
A summary of crop yields for a series of years should be accom- 
panied by a statement of the physical factors that influence crop 
production. The most important physical factors are (1) the soil; 
(2) the seasonal and annual rainfall; (8) the seasonal evaporation; 
(4) the wind, with special reference to that which passes directly over 
the ground surface during the growth of the crop; and (5) the tem- 
perature, especially the killing frosts of spring and autumn that limit 
the growing season. The data on these factors, which follow, have 
been recorded at the Williston substation and at the station of the 
United States Weather Bureau in Williston. 
sotu.! 
The soil of the Williston substation is of an alluvial character, but 
it is variable in type. It is not typical of most of the best farming 
land outside of the valley. The creek-bottom flat consists of a heavy 
clay of the type described by the Bureau of Soils as Laurel clay. 
The larger portion of the substation consists of level or rolling land 
somewhat higher than the creek bottom. The somewhat variable 
soil on this portion is of the type known as Williston sandy loam. 
Water for irrigation is available on this part of the station farm. 
- That portion of the substation where the cereal experiments are 
conducted consists of a fairly level upland area, on which irrigation 
water is not available. The soil, which is fairly uniform in type, is 
classed as Laurel fine sandy loam. 
NATIVE VEGETATION. 
A biological survey was made of the Williston area in 1906.2, The 
most important native vegetation found prevailing on the prairie 
included grama grass (Bouteloua oligostachya), buffalo grass (Bul- 
bulis dactyloides), western wheat-grass (Agropyron occidentale), slender 
wheat-grass (Agropyron tenerum), and needle grass (Stipa comata 
and Stipa viridula). The grama grass grows abundantly over the 
prairie and makes a very nutritious pasture and excellent hay. The 
buffalo grass is just as nutritious, but is found more in spots and is 
never tall enough for hay. The western and slender wheat-grasses 
are found in the wild state and will replace the other native grasses 
when the sod is broken. They are grown extensively for the produc- 
tion of hay. 
RAINFALL. 
Table I shows the precipitation record for the Williston locality 
for a period of 36 years, from 1879 to 1914, inclusive. Previous to 
1893 the weather records were kept at Fort Buford, N. Dak., 20 
1 For a full report on the soils of the Williston locality, see Rice, T. D., Willard, R. E.,and Weaver, J. suas 
Soil survey of the Williston area, North Dakota, In U.S. Dept. Agr. Bur. Soils Field Oper. 1906, 8th Rpt., 
p. 999-1022, fig. 34, 1908. . 
*Bell, W. B. Report of the biological survey of North Dakota. In 4th Bien. Rpt. Agr. Col. Sur- 
vey N. Dak., p. 28-51, 1910. 
