THE EFFECTIVE ,USE OF LAND AS SHOWN BY YIELD 25 
TABLE 7.—Actual and theoretical total combined annual production of corn, 
wheat, oats, and potatoes (average 1920-1924) in selected regions 
[Millions—i. e., 000,000 omitted] 
NT 
Middle East N orthern Total for 
T section of 
Item Atlantic North South three 
: : Central : State 
States AH Atlantic 
States States groups 
Actual total annual production of four crops on average acreage | Bushels | Bushels | Bushels | Bushels 
utilized annually, 1920-1924. ___________________---_-__--.----- 289.9 | 1,388.9 226.6] 1,905.4 
Theoretical total annual production of four crops on average ‘ 
acreage utilized annually, 1920-1924, but at average acre-yield 
level prevailing in 1985-1889: 22. os = en pace noe, es a 199:-71- Bh tt63 127.8 1, 438.8 
Calculated increase in totalsupply available annually as aresult 
olinighortyieldS*> - 255s. t2 Sk fe ee er 25 Ese 90. 2 277.6 98. 8 466. 6 
From the foregoing it is apparent that the rise in yields in these 
three regions accounted for more than half of the total increase in 
productivity (because of higher yields of these four crops) in the 
United States as a whole. It will be noted also that the Middle At- 
lantic States, the northern section of the South Atlantic States, and 
a considerable portion of the East North Central States comprise a 
large part of the oldest cultivated portion of the United States. 
SUMMARY AND CONCLUSIONS 
Looking backward over the last 150 years we can see the effects 
of different methods brought into use in the course of the so-called 
agricultural revolution. In western Europe the period witnessed an 
enormous increase in productivity owing mainly to the rise in crop 
yields. As a result, first, of the revival in the use of soil-manage- 
ment methods known to the Romans and aiter the middle of the 
nineteenth century by the added developments in the field of agri- 
cultural chemistry resulting from the discoveries of Liebig and 
others, and improvements in technique following research in various 
branches of natural science, the productive capacity of the soils of 
northwestern Kurope was greatly increased. Wheat yields per acre 
rose gradually from a level ranging between 6 and 10 bushels per 
acre in the various countries to a level of 20 bushels per acre in 
France and over 32 bushels per acre in England and Germany. In 
the smaller countries such as Denmark, with relatively small areas 
in grain crops, even higher acre-yields were obtained. ‘The acre- 
yield of other crops in these countries was also increased considerably. 
In the United States, considered as a whole, the statistical record 
of crop yields per acre for our important food and feed crops dur- 
ing the last 40 years indicates a generally rising trend. Especially 
in the latter half of this period much of the expansion of our crop 
area, particularly that occurring in our wheat acreage, was on sem1- 
arid lands with relatively low average yields per acre. _ 
Analysis of the statistics of crop yields of the individual States 
indicates that the outstanding increase in yield per acre of crops 
have occurred in the northeastern portion of the United States, in- 
cluding the noftthern half of the South Atlantic States. It is in 
these States that, with the passing of the old-time pioneer methods 
and with an increasing widespread use of improved soil-management 
