42 BULLETIN 1173, U. S. DEPARTMENT OF AGRICULTURE. 
of the former. The double plowing showed an advantage of 2.6 © 
bushels per acre over spring plowing. From results in somewhat 
similar tests elsewhere double plowing does not seem justified unless 
necessary to control weeds. 
Judged by the results of this experiment from 1916 to 1921, inclu- 
sive, it is probable that under conditions similar to those at Nephi, 
Utah, cultivation other than that required to control weeds does not 
pay for the extra labor. 
TILLAGE FACTORS INFLUENCING YIELDS AND QUALITY OF WINTER WHEAT. 
It has been generally accepted without question that the chief 
purpose of the summer-fallow system is to save moisture for use by 
the crop during the next season. There are other effects of tillage, 
however, which have a very important bearing on production and 
should not be overlooked in considering the problem of the fallow. 
Indirectly, because of its influence on soil temperature, aeration, 
moisture location, etc., tillage has a very marked effect in promoting 
the activities of soil bacteria; and as a result of this activity and the 
direct effect of soil stirrmg and moisture additions the chemical 
make-up of the soil and consequently the availability of plant food 
are very materially altered by tillage. 
At Lind in the past four seasons and at Moro in the past two seasons 
the moisture studies of the summer-fallow tillage experiments were 
accompanied by soil studies of nitrate nitrogen, and while not yet 
conclusive these studies brought out certain interesting facts. It is 
not intended to present the data obtained from these studies in this 
bulletin, yet this phase of tillage effects is so important that it should 
at least be briefly considered. 
Each year there were differences in yield from different methods of 
fallow treatment, and the moisture studies show that these yield 
differences were not entirely attributable to moisture variations. In 
a season when rainfall is comparatively abundant, the entire soil body 
to the depth ordinarily reached by plant roots may be filled with 
moisture, and in such cases variations in yield can not be attributed 
to differences in moisture supply. The nitrate-nitrogen studies 
show, however, that early clean tillage, in particular, promotes the 
development of nitrate nitrogen in the soil and that after a year of 
fallow there are much larger supplies of this plant food in those soils 
receiving early clean tillage than in those plowed at a late date or on 
which weeds have been allowed to grow. In years of abundant 
moisture the yields very closely parallel the soil content of nitrate 
nitrogen, provided this available nitrogen is not removed by leaching 
during the winter following the year of fallow. 
Not only have there been differences in yield but also wide varia- 
tions in the habit and manner of plant growth and in the quality of 
the wheat produced on the different fallows. On the jute pee 
pee not previously cultivated to keep down weeds and which were 
ow in content of nitrate nitrogen at seeding time, the plants were a 
lighter green in color, tillered less, had fewer and smaller leaves, grew 
more slowly, and when mature usually had more slender culms than 
those plants grown on the early-plowed plats which were cultivated 
at frequent intervals during the fallow season and had a greater 
content of nitrate nitrogen in the soil. 
