64 BULLETIN 1377, U. S. DEPARTMENT OF AGRICULTURE 
a 1-crop system of farming, the average crop yields of a farm or 
community or of the whole country can be greatly increased if to 
cultivation is added crop rotation, and can be further increased if to 
cultivation and rotation, in turn, is added the use of fertilizers. 
If conditions were such as to make possible the application of so 
simple a productivity program, the food-production problem of the 
Nation would not prove a serious one for many years to come. The 
general conditions as they exist, however, call for a very different 
interpretation or application of the facts brought forth as a result of 
this study. 
Cultivation is generally practiced. Rotation of some description 
is practiced by most farmers, though the rotation may consist in 
merely a change of crops without any definite system or any degree of 
regularity. Manure, wherever it is produced, is usually disposed of 
for the good of the land; and commercial fertilizers are coming more 
and more into use, either specially in single or incomplete forms to 
correct certain soil deficiencies or to meet the requirements of special 
crops, or generall} T in mixed or complete forms. 
From the point of view of the country at large, any increase in the 
average crop yields as effected by cultivation is possible only when a 
general improvement is made in tillage methods or practices. Such 
effects can be realized only to the extent that each individual farmer 
masters the fundamental principles of tillage and studies his soils, 
crops, and machinery so as to enable him to make the proper appli- 
cation of the tillage principles to the conditions on his farm through 
the means at his command. 
Farm manure and commercial fertilizers seem to be regarded as 
possessing the greatest possibilities with reference to maintaining 
soil productivity and in effecting increases in crop yields. Judging 
from the experiences of farmers who have used such materials as 
dung, seaweed ashes, wood ashes, street refuse, and certain kinds of 
marl during pre-Roman and Roman times, and from the profound 
effects that manufactured or commercial fertilizers have had, since 
1840, on the agriculture of the leading nations of the world, the basis 
for the recognition of great possibilities in fertilizers is well grounded. 
Generall} 7 speaking, over against the great possibilities of the use 
of fertilizers in maintaining and increasing soil productivity are to 
be placed the possibilities of crop rotation, which have been found to 
exceed very often those of the use of manure or chemical fertilizers. 
Though it is true that most farmers alternate their crops in one 
manner or another, the maximum effects of crop rotation certainly 
are not reflected in the average crop yields of the agricultural regions 
of the United States, or of the United States as a whole. There can 
be little doubt that rotation can be made much more effective in 
increasing as well as in maintaining crop yields, not only in sections 
in which fertilizer practices have become more or less permanently 
established, but as well in sections in which commercial fertilizers 
are sparingly used, or are still practically unknown. 
Since it has been found that rigid or fixed rotations are very often 
more effective than the use of fertilizers in increasing the yields of 
such crops as wheat, corn, and oats, it seems reasonable to assume that 
properly planned, flexible rotations would prove even more effective 
in practical farming, both from the productivity and economic points 
of view. 
