50 BULLETIN 1301, U. S. DEPARTMENT OF AGRICULTURE 
Rotations 1 to 9, inclusive, are repeated three times in the main 
field. Each of these rotations appears in series I, series II, and 
series III, and each block of 27 plats across the three series also 
contains each of the nine rotations. The results from these rotations 
show that if the yields of any one of the combinations were used, 
the conclusions would not be changed from those derived from any 
other set. 
The land upon which the rotations are located was broken during 
May and June, 1913, and backset in the fall. The yields of all crops 
were high in 1914 because of the very favorable season. The 1914 
yields are not included in any of the tables presented, because all 
crops were on land given uniform treatment. 
The yields following summer fallow in 1915 are not entirely com- 
parable with those following other tillage methods or those of other 
years, because the plats were not only fallow in 1914 but were semi- 
“ 
fallow in 1913. 
SPRING WHEAT 
The yields of sprmg wheat from the main and south fields for 
the years, 1915 to 1922, inclusive, are presented in Table 16. The 
wheat yields for the 3-year period, 1919-1921, inclusive, were low, be- 
cause of the dry seasons. While 1917 and 1918 were also dry, the 
yields under most of the cultural methods were not exceedingly low. 
In a comparison of wheat yields following different cultural treat- 
ments, disked potato ground has produced a yield equal to that on 
summer fallow. Disked potato ground is an excellent preparation 
for wheat. The one plat receiving this preparation is in a 4-year 
rotation which contains manured summer fallow in addition to the 
potatoes. That the high yield following potatoes is not due to the 
manure in the rotation is indicated by the results from a similar 
rotation containing manured fallow, in which the potatoes are re- 
placed by corn. The yield of wheat in this rotation is not above the ~ 
average on disked corn ground in rotations that receive no manure. 
In discussing the yields from summer-fallowed land, it should not be 
forgotten that twice as much land is required to produce the yields 
on fallow as on land continuously cropped. As much land is needed 
for a crop of wheat on fallow as is required to produce a crop of 
wheat and one of corn or potatoes. If the land is to produce equal 
values, the value of the crop after summer fallow should equal 
the combined values of the crop of wheat and the crop of corn or 
potatoes that take the place of the fallow. In the case of continuous 
cropping, the value of the crop on summer fallow should equal 
two continuous-cropping crops. 
The yields in Table 16 show the following points: Plowing corn 
eround, instead of disking it, for wheat has not increased the yield 
enough to pay for the labor of plowing. Spring plowing for wheat 
has been slightly better than fall plowing. Land manured before 
plowing for summer fallow has produced higher yields than unma- 
nured land. Crops turned under for green manure have not increased 
the yields over summer fallow. The yields indicate that the green 
manure, as compared with fallow, has a depressing effect on yields, 
but the reason for the difference may be found in the time of plowing 
under the green manure and the time of plowing for fallow. The sub- 
soiled plat, which is directly comparable to the fall-plowed plat after 
