18 



BULLETIN 705, U. S. DEPARTMENT OF AGEICULTUBE. 



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 XIII 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 

 Polk 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.S7 



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 sununer 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 jaeld 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 



