16 CIRCULAR 421, U. S. DEPARTMENT OF AGRICULTURE 



duction program that will permit the best use of barley as a feed 

 are steps forward in establishing a well-balanced farm program. 



COMPARISON OF SMAIX GRAINS GROWN CONTINUOUSLY WITH SMALL GRAINS FOLLOW- 

 ING SMALL GRAIN IN 3-YEAR ROTATIONS CONTAINING A CULTIVATED CROP 



The 20-year average yields of grains following grains in 3-year 

 rotations containing a cultivated crop were more than 20 percent 

 higher than those of grains produced under continuous cropping. 

 This difference did not appear during the early years of the experi- 

 ments, but was in evidence from 1916 to 1932. The extent of the 

 difference varied with the character of the season. In the produc- 

 tive year of 1927, the yields of grains grown continuously on the same 

 land were materially higher than those of grains after grain in the 

 3-year rotations. The same relation appeared for some crops in 

 1915 and 1918, but the differences were smaller. In general, the 

 yield of grain after grain in the 3-year rotations showed the greatest 

 increase over continuous cropping in years in which drought injury 

 was above the average but not severe enough to cause a nearly com- 

 plete failure. In productive years the difference was generally 

 small. 



The fact that the same condition was true for all crops makes it 

 appear positive that the benefit derived from growing a cultivated 

 crop extends to the second crop following. The carry-over is suffi- 

 cient to increase yields materially in years of drought injury. 



COMPARISON OF Y IELD S OF CORN AND SORGO IN DIFFERENT CROP SEQUENCES 



The effect of sequence on the yields of corn and sorgo is shown 

 in table 7. As with small grains, the effect of plot variation is re- 

 duced by the inclusion of as many plots as possible. For example, 

 the yield of corn after small grain represents the average }deld ob- 

 tained from all plots where corn followed small grain, regardless 

 of the length of the rotation, the grain crop, or the method of cultiva- 

 tion under which the corn was grown. Corn was grown after corn 

 only under a continuous cropping system, and only one plot was 

 grown on fallowed land. Sorgo was grown after sorgo only under a 

 continuous cropping system. Only one plot of sorgo was grown on 

 fallowed land. 



