4 BULLETIN 1155, U. S. DEPARTMENT OF AGRICULTURE. 
cated by color is quite high. It is probably the most pronounced 
adobe soil in the Sacramento Valley and but for its adobe structure 
would be almost impossible to till. The dark-colored surface soil 
grades into lighter colored buff, light-brown, brownish yellow, or 
yellowish clays at depths varying from 18 to 36 inches. 
The subsoil is distinctly calcareous and between the soil and subsoil 
there is usually a well-defined impervious calcareous hardpan. The 
soil holds water well, but cracks and checks badly when thoroughly 
dry and is very difficult to work when either too wet or too dry. 
When plowed wet and exposed to rain and sunshine, this soil breaks 
down into a mass of pea-sized particles. 
The principal soils on which rice is grown in the Sacramento Valley 
are the clays and clay adobes of the Stockton. Willows, Sacramento, 
Capay, and Yolo series. The soil at the station is representative of 
a large part of the area on which rice is grown in California. The 
Fig. 1.— Buildings at the Biggs Rice Field Station, Biggs, Calif. 
results obtained at the Biggs Rice Field Station are applicable in a 
general way to other sections of the Sacramento Valley in which rice 
is grown. However, on the lighter soils and in sections where alkali 
is much in evidence, a slightly different method of irrigation may be 
necessarv to secure the best results. 4 
TEMPERATURE. 
The Sacramento Valley is subject to wide ranges of temperature. 
The winters are comparatively cool, but temperatures below 20° F. 
are seldom recorded, and freezing weather is infrequent. The springs 
are warm and the summers are hot, though the summer nights are 
usually comparatively cool. The fall is usually warm but seldom hot. 
Table 2 presents data showing the maximum, minimum, and great- 
est range in temperature from April 1 to October 31 in the 9-year 
period from 1913 to 1921, inclusive. 
* Adams, Frank. Rice irrigation measurements and experiments in Sacramento Valley, 1914-1919. 
Calif. Agr. Exp. Sta. Bui. 325, p. 45-69, 4 fig. 1920. 
