20 BULLETIN 1458, U. S. DEPARTMENT OF AGRICULTURE 
Tn the States where the crop area spread into the semiarid region 
the effect of this expansion can be seen in the lower crop yield level, 
which, as already suggested, exerted considerable influence in de- 
pressing or holding down the average yields for the Nation as a 
whole. 
The record of the past four decades indicates that the great out- 
standing changes have occurred in the North and South Atlantic 
States and lesser changes in the East North Central States. Like 
changes have also occurred in many portions of the West North 
Central States, where pioneer agricultural methods have disap- 
peared. In the case of corn yields especially a marked rise has taken 
place in the northern portion of the South Atlantic States. In a 
general way these sections comprise the oldest farming regions in 
the United States. In these regions the soils have already entered 
or are now entering the period of permanent use, and the pioneer 
methods of the last century are largely memories only. 
The averages for the various States during the last 40 years show 
the following increases for corn yields: In the North Atlantic States 
from 6 to 10 bushels per acre; in the Kast. North Central group from 
6 to 12 bushels; and in the northern section of the South Atlantic 
States (comprising Delaware, Maryland, Virginia, West Virginia, 
and North Carolina) from 9 to 14 bushels per acre. The averages 
of the quinquennial period of 1885-1889 compared with the averages 
during the half decade of 1920-1924 in Iowa and Minnesota show, 
respectively, increases of 8 bushels and 6 bushels per acre. Sarle, 
formerly of Iowa, has pointed out the consistent and state-wide 
rising trend of corn yields in that State (70). In each of the nine 
crop-reporting districts during a period of 33 years (1890-1923) the 
trend of acre-yields has been upward. 
The record of wheat yields for the several States shows a rise 
during the period of from 5 to 6 bushels per acre in the northeastern 
portion of the United States. In Ohio and other States in the Ohio 
Valley a marked decrease occurred in the average wheat yields for 
the period 1920-1924. This was largely the result of unfavorable 
weather conditions during the years 1920-1922, inclusive. The de- 
crease is probably only temporary, and with normal weather condi- 
tions a recovery to the higher level of yields will probably take place. 
In Kansas, in spite of the expansion of the wheat area into the semi- 
arid portion of the State, yields have remained practically stationary 
for the entire period. In Missouri, on a considerably expanded 
wheat area, yields of that crop have remained lew and practically 
stationary. Statistics of yield per acre seem to suggest that the 
southern part of the Corn Belt, as represented by Missouri and 
eastern Kansas, has lagged behind the northern portion, as repre- 
sented by Iowa and Illinois, in the development of agricultural prac- 
tices and soil-management methods that tended to raise the acre- 
yields of the important crops. 
In the spring-wheat region the continuance of pioneer methods 
and the continued expansion of wheat production into drier areas 
has prevented a rise in the State averages of acre-yields. Since mois- 
ture is commonly the limiting factor in crop production in the semi- 
arid portions of the Plains States, it appears probable that this part 
of the United States will not experience—at least, in equal degree— 
ia 
