TILLAGE AND ROTATION EXPERIMENTS, NORTH DAKOTA 15 
were turned under at their maximum growth and the land kept free 
from weeds during the remainder of the season and cropped to 
either wheat or oats the following year. This method of handling 
the green manure made it more comparable to fallow than to any 
other tillage method. Fallow plats as a rule were plowed early 
enough to prevent much loss of moisture by weed growth, but 
in many seasons the growth of rye, peas, or sweet clover for green 
manure almost or entirely exhausted the available soil water by 
plowing time. The average dates of plowing fallow and the green- 
manure crops were : Fallow, June 21 ; rye, July 1 ; peas, July 11 ; and 
sweet clover, July 6. During the five-year period from 1919 to 1923 
the average date of plowing fallow at Dickinson was June 5, show- 
ing the general adoption there of the more recent practice of early 
plowing. In experiments on the time of plowing fallow conducted 
at other stations, delayed plowing shows reduced yields, which cor- 
respond very closely to those which follow the late plowing of green- 
manure crops. 
The green-manure rotations are as follows: 
No. 14, Rye, oats, corn, and wheat. 
No. 15, Rye, wheat, corn, and oats. 
No. 16, Peas, oats, corn, and wheat. 
No. 17, Peas, wheat, corn, and oats. 
No. 31, Sweet clover, oats, corn, and wheat. 
No. 32, Sweet clover, wheat, corn, and oats. 
No. 61, Peas, wheat, and oats. 
No. 63, Rye, wheat, and oats. 
All of these were included in the experiments at Dickinson, all 
but the last two at Hettinger, and all but the last three at Williston. 
Other rotations previously described containing fallow are di- 
rectly comparable with these containing green manure. Rotation 
No. 18 is fallow, wheat, corn, and oats and rotation No. 19 fallow, 
oats, corn, and wheat. Rotation No. 5 is a three-year rotation con- 
taining wheat on fallow and oats on fall-plowed wheat stubble, and 
rotation No. 8 is a similar rotation in which the oats are on fallow 
and are followed by wheat. 
Small grains, the first crop following green manure, averaged 
less than following bare fallow, the method most comparable with 
green manure, and with the exception of oats at Dickinson and 
wheat at Williston the yields were less than on disked corn ground. 
Table 8 shows that wheat averaged 16.5 bushels on disked corn 
ground, 18.8 bushels on fallow, and 15.8 bushels following green 
manure at the three stations. Oats in a similar comparison aver- 
aged 35.1 bushels on disked corn ground, 40.3 bushels on fallow, 
and 33.9 bushels after green manure. 
A legume has been of no more value than a nonlegume for plow- 
ing under. The yields of wheat after both peas and sweet clover 
were slightly less than after rye, but the differences were too small 
to be significant. At Dickinson oats after rye averaged 40.7, after 
peas 37.7, and after sweet clover 39.2 bushels per acre. At Het- 
tinger the average after rye was 29.8, after peas 27.2. and after sweet 
clover 31.7 bushels, indicating a slight advantage for sweet clover. 
The yield of corn silage at Hettinger also was higher in the sweet - 
clover rotations. 
