4 BULLETIN 336, U. S. DEPARTMENT OF AGRICULTURE. 
variable depth.. It is known locally as brick clay. The general soil 
type in its natural condition is difficult to cultivate. The extensive 
and continued use of green-manuring crops, commercial fertilizers, 
and lime, with, the installation of a complete system of tile drainage, 
has greatly improved its physical condition as well as eliminated to 
a large degree the lack of uniformity in productiveness. The texture 
has been improved, thus rendering it easier to cultivate and more 
congenial to plant growth. This soil probably would be classed as 
Susquehanna clay, a type that usually is not well adapted to grain 
growing. 
CLIMATIC CONDITIONS. 
Rainfall in the eastern half of the United States is not usually an 
important limiting factor in crop production. Other general phys- 
ical phenomena, such as wind and evaporation, also are not of great 
importance; consequently they are not used so much as an index to 
crop production as in the semiarid areas. Soil fertility is one of the 
most important factors in crop production throughout all the older 
agricultural regions in the eastern United States. 
The most serious climatic condition encountered in the experi- 
mental work with cereals at College Park and Arlington has been 
the occurrence of hot, humid, showery weather during the ripening 
period, causing the rapid development of rust, scab, and other dis- 
eases. This has been more particularly true with reference to winter 
wheat, as winter oats and barley usually escape because of earlier 
maturity. In some years short periods of drought undoubtedly affect 
these crops, but in general they are not of serious consequence. 
In the pages which follow, data are given on the rainfall and tem- 
perature for the period from 1905 to 1914. These data were recorded 
at the Weather Bureau station in Washington, D. C, about 10 miles 
west of College Park and about 2 miles north of the Arlington Farm. 
RAINFALL. 
The annual and average precipitation by months at Washington, 
D. C, for the 10 crop years from July, 1904, to June, 1914, inclusive, 
are shown in Table I. Weather data are now recorded at Arlington 
Farm, but as these data are available only since October, 1910, it 
was deemed advisable to use the data in full from the Weather 
Bureau station in Washington. 
The average annual precipitation at Washington for the 10 crop 
years from July, 1904, to June, 1914, inclusive, as shown in Table I, 
was 42.33 inches. For this period the maximum annual precipi- 
tation was 53.47 inches (1906-7), and the minimum, 33.22 inches 
(1910-11). 
Table I shows that August is usually the wettest month, while 
November is the driest. The average annual precipitation at College 
