18 
BULLETIN 705, U. S. DEPARTMENT OF AGRICULTURE. 
having no clover. Likewise the average yields of potatoes, wheat, 
and oats for the group of 38 farms having an average of 32.7 per cent 
of the field-crop area in clover were 17 per cent, 21 per cent, and 33 
per cent higher than the yields of these crops for the group having 
no clover. 
RELATION OF SUMMER FALLOW TO CROP YIELDS. 
In considering the influence of summer fallow on crop yields, it 
must be remembered that 40 to 50 years ago the practice of summer ■ 
fallowing the land once every three or four years was extensively 
followed in the Willamette Valley on both the clay and silt loam types 
of soil; that this practice is still generally followed on the clay soil, 
but has almost disappeared on the silt loam soil. Table XITI shows 
the comparative yields of potatoes, wheat, oats, and hay on both the 
clay and silt loam farms with and without summer fallow. 
Table XIII. — Relation of summer fallow to crop yields on 212 farms in Marion and 
Folk Counties, Oreg. (1912). 
Item. 
Salem clay. 
Without 
summer 
fallow. 
With 
summer 
fallow. 
Salem silt loam. 
Without 
summer 
fallow. 
With 
summer 
fallow. 
Number of farms 
Crop yields per acre: 
Potatoes (bushels) 
Wheat (bushels) . . 
Oats (bushels) 
Hay (tons) 
Crop index 
11 
177.8 
23.9 
27.0 
1.87 
90 
57 
192.6 
25.3 
31.2 
2.04 
101 
127 
155.9 
21.9 
37.9 
1.94 
101 
17 
98.4 
23.5 
36.5 
1.76 
96 
From Table XIII it will be noted that 57 of the 68 clay farms had 
more or less tillable land lying idle as summer fallow, and that only 
17 of the 144 silt-loam farms were still practicing the summer-fallow 
method. The clay farms having summer fallow had higher crop 
yields than the clay farms having no summer fallow, the relative 
crop index of the groups with and without summer fallow being 101 
and 90, respectively. On the other hand, the silt loam farms having 
no summer fallow had higher crop yields, for all crops except wheat, 
than the few farms practicing summer fallowing. Because wheat 
follows summer fallow, its yield should be affected by summer fallow 
more than the yield of any other crop. The crop index of the silt 
loam farms having no summer fallow was 101, whereas that of the 
17 farms with summer fallow was 96. 
It appears, therefore, that on the silt loam farms having no sum- 
mer fallow, cropping systems have been adopted that give higher 
crop yields than are secured on the 17 farms still practicing summer 
fallowing. This has been accomplished, it is safe to say, by the in- 
troduction of the leguminous crops. It is reasonably certain that 
