14 BEXLETIX 991, TJ. S. DEPARTMENT OE AGRICrTTTTBE. 
of wheat has been four-tenths of a bushel less on fallow than on disked 
corn ground. The yield of corn in rotation No. 19, which shows the 
greater yield of both oats and wheat, is also slightly higher than in 
rotation No. IS. 
In section 9 the oats on fallow have averaged 2.7 bushels more than 
on corn ground, and the wheat 3.4 bushels more. 
MANURED COMPARED WITH UNMANURED FALLOW. 
Xos. IS. 19. 71. and 72 are 4-year rotations. The first two were 
started in 1907 and the others in 1908. Nos. IS and 72 are fallow, 
wheat, corn, and oats. Xos. 19 and 71 are fallow, oats. corn, and 
wheat. The fallow in Xos. 71 and 72 receives 10 tons of rotted barn- 
yard manure per acre before plowing. In the 11 years from 1909 
to 1919 each crop in the manured rotations has averaged higher yields 
of both grain and straw than the corresponding crop in the un- 
manured rotations. The average increases, however, have been small, 
the highest being 1| bushels for wheat on fallow. 
What appears to be the true significance of the value of manure in 
a rotation is shown when the results are studied in another way. 
The crops are now being grown on land that has been manured the 
third time. \Yhen the results are studied in detail from year to year 
or grouped and studied in periods of no manure in the first years, 
manured once, manured twice, and manured three times, it is shown 
rather clearly that the use of manure on fallow once in four years 
not only increases the yields of the three crops in the rotation but has 
a cumulative effect, the increase becoming greater with each round of 
the rotation. Before the corn came on the manured land in rotations 
Xos. 71 and 72 the total weight of corn from these rotations averaged 
only 151 pounds per acre more than in rotations Xos. 18 and 19. 
TThen the land had been manured once the increase was 750 pounds : 
manured twice. 9S3 pounds : and manured three times. 1,138 pounds 
per acre. 
The yields of wheat and oats are affected by the fact that in very 
favorable seasons the manure increases the tendency to lodge and 
to rust, but in the second and third roimds of manuring these crops 
show decided increases on the manured land. 
It is a difficult question to study, but all evidence points to the 
belief that the observed differences are due to an increase in the 
manured rotations rather than to any deterioration or reduction in 
the original yielding power of the unnianurecl rotations. 
These rotations are duplicated on section 9. but the rotations have 
only been one round in this location. The differences in any exhibi- 
tion of yields are not as yet great enough to be distinguished from or 
among the natural differences due to soil variation. 
GREEN MANURE COMPARED WITH BARE FALLOW. 
At the time these experiments began it was thought that green 
manures might possibly offer a means of increasing or maintaining 
