% BULLETIN 222, IT. S. DEPARTMENT OF AGRICULTURE. 
conducted at fourteen different stations in the Great Plains area. 
Barley has been grown to a minor extent in the rotations at all sta- 
tions, although it has not been considered as important a crop as 
either wheat or oats. 
At some of the stations the work has been continuous for ei°-ht 
years; at other stations it has been but recently started. The 
results of the first year's work at any station are not used, as the land 
is uniform in preparation for all plats. From the stations having the 
longer records the results are the most valuable, since they include 
a greater range of climatic conditions. Where a short record is given 
it can show only the effect of the different tillage methods under the 
particular combinations of climatic factors obtaining during that 
time. The crop on any series of plats having the same methods of 
tillage may behave quite differently under the combinations of 
climatic factors that may occur in succeeding years. The relative 
position assumed by the various methods in the first year's results 
may or may not .be changed from that arrangement by subsequent 
work. It is certain, however, that the range of difference between 
the methods will vary with changing climatic factors. Wide differ- 
ences in yields between methods that may be shown in a short record 
will tend to be narrowed as the length of the record is increased. 
The method of work adopted was that of raising the standard crops 
of each station both in rotations and by different methods of prepara- 
tion under systems of continuous cropping. In no case have rotations 
requiring more than six years been used. Those of even this length 
have been tried only when sod of tame-grass crops is included. 
More of the work has been done with 3-year and 4-year rotations. 
In this bulletin are shown only the crop immediately preceding 
and the tillage involved in preparing the seed bed for barley. In the 
present stage of development of the work the effect of the imme- 
diately preceding crop and of the method of handling its stubble 
in preparing the seed bed greatly overshadows the effects of the ro- 
tations considered as units. Some of the rotations are calculated to 
conserve or to accumulate fertility and organic matter in the soil, 
while others may perhaps deplete it, but on the naturally fertile 
soils of the Plains such results are not strongly shown in the first 
years of treatment. The controllable factors that exert the greatest 
influence on production are the water supply, the physical condition 
of the seed bed, and a recognized, if not understood, effect of the 
immediately preceding crop. The crop of a single year brings the 
land back to so near uniformity in these factors that their probable 
residual effect is not great enough with the work in hand to introduce 
serious error into the study here made. 
This bulletin, which deals with only one crop, does not afford any 
criterion by which to judge the agricultural possibilities of any sec- 
