38 BULLETIN 1421, U. S. DEPARTMENT OF AGRICULTURE 
alfalfa occupied the land two years in a 4-year rotation and about 
one and one-half times as great as when the alfalfa occupied the land 
three years in a 6-year rotation. The alfalfa in these rotations is 
seeded alone in the spring. Troublesome weeds make it necessary 
to clip the young alfalfa two or three times and as a consequence little 
or no hay is made the first year. This materially reduces the average 
yield for the rotation period. The yield of oats was also about 3 
bushels less per acre when grown in a 2-year rotation with wheat 
than when grown continuously on the same land. 
The yield of wheat, corn, potatoes, sugar beets, and oats was 
increased in each case, except as noted above, by the rotation of crops — 
when compared with the yield of each crop grown continuously on 
the same land. The increase in the yield of each crop was striking 
in each case, where alfalfa had a place in the rotation (rotations 40, 
42,44, 48,60, and 62). The increase was not very great, on the other 
hand, in the rotations not containing alfalfa (rotations 16, 18, 20, 
22, 24, 26, 28, and 30) with the exception of potatoes. In all cases the 
rotation of crops materially increased the yield of this crop. 
Table 18 also shows that there is considerable variation in the 
influence that the respective crops have on the yield of other crops 
in the rotation with which they are grown. For example the average 
yields of sugar beets when grown in 2-year rotations were 8.9 tons per 
acre when grown with wheat, 10 tons per acre when grown with oats, 
and 10.7 tons per acre when grown with potatoes. The yields of oats 
were 37, 45, 48, and 52 bushels per acre, respectively, when grown in 
2-year rotations with wheat, corn, potatoes, and beets. The yields 
of potatoes grown in 2-year rotations were 104 bushels per acre after 
corn, 111 bushels after sugar beets, and 123 bushels after oats. A 
study of the yields of the crops grown in the alfalfa rotations indicates 
that potatoes are by far the best crop to plant on alfalfa sod when 
measured by the increase in the yield obtained. 
Effect of adding alfalfa to the rotation on crop yrelds.—A comparison 
of the yields obtained from (1) rotations 28 and 48, (2) rotations 22. 
and 42, (3) rotations 20 and 40, (4) rotations 24 and 44, (5) rotations 
32 and 62, and (6) rotations 30 and 60 show the effect on crop yields 
of adding alfalfa to the rotation. The addition of two years of alfalfa 
(1) to rotation 28 increased the yield of wheat 9 bushels per acre 
and that of oats 25 bushels; (2) to rotation 22 increased the yield of 
oats 13 bushels per acre and that of sugar beets 6.7 tons; (3) to rota- 
tion 20 increased the yield of potatoes 135 bushels per acre, and that 
of sugar beets 7.2 tons; and (4) to rotation 24 increased the yield of 
potatoes 103 bushels per acre, and that of oats 17 bushels. Likewise 
the addition of three years of alfalfa (1) to rotation 32 increased the 
yield of corn 22 bushels per acre, that of oats 19 bushels, and that 
of sugar beets 4.8 tons; and (2) to rotation 30 increased the yield of 
potatoes 125 bushels per acre, that of oats 11 bushels, and that of 
sugar beets 5 tons. 
Effect of barnyard manure on crop yields——A comparison of the 
yields obtained from (1) rotations 22 and 23, (2) rotations 20 and 21, 
(3) rotations 24 and 25, and (4) rotations 30 and 31 shows the effect 
of the manure applied in these experiments on the yields of the crops 
in the respective rotations. The application of 12 tons of manure 
per acre once in the rotation period (1) to rotation 23 increased the 
average yield of oats 12 bushels per acre and that of sugar beets 
