154 



THIRD ANNUAL SESSIONS 



3. Yield of Oats on spring- plowed land after Oats. 



4. Yield of Oats on fall plowed land after Oats. 



5. Yield of Oats on spring plowed land after Corn. 



G. Blank, no Oats having been grown on fall plowed Corn ground. 

 7. Yield of Oats on land disked but not plowed after Corn. 

 8 Yield of Oats on fallow or summer tilled land. 



9. Yield of Oats on land which had Rye plowed under for green manure. 



10. Yield of Oats on land which had Peas plowed under for green manure 



11. Yield of Oats on land which had Sweet Clover plowed under for green manure. 



12. Yield of Oats on fall plowed land after Barley. 



13. Yield of Oats on fall plowed land after Flax. 



The lower half of this diagram shows the same data for Wheat that the 

 upper half does for Oats. 



cerning the danger in figuring conclusions from too limited expeninnce. 

 If one were to consult a single station or a single year almost any- 

 kind of a theory could be supported, but when we take into considera- 

 tion the net results of all the years at the different stations, it will be 

 found that no such hard and fast rule can be established. 



"Dr. L. J. Briggs, Physicist of our Bureau, will now present some 

 of the physical and meteorological data which he has obtained in con- 

 nect'on with the work which I have just described." 



PHYSICAL PROBLEMS IN CONNECTION WITH DRY 

 FARMING. 



By L. J. Briggs and J. O. Belz, Physical Laboratory, Bureau of Plant 

 Industry, Department of Agriculture. 



"The annual rainfall is frequently the only factor considered in the 

 selection of a dry farm. The object of this paper is to point out certain 

 other factors that often determine the success or failure of dry farming 

 operations. 



Precipitation. 



"Rainfall records in the Great Plains are now available for a period 

 of thirty-four years. This gives a very satisfactory basts from which to 

 calculate the normal rainfall. The average annual rain for the whole 

 period is about 21 inches. The yearly rainfall for the past thirty-four 

 years for the Great Plains is shown in the accompanying chart (Figure 1). 

 The number of stations on which the records are based is given at the 

 bottom of the diagram. The early records were taken mainly at forts, 

 and are necessarily somewhat incomplete. The highest rainfall dur.ng 

 the latter part of this period occurred in 1905, when the average for the 

 whole region was 27 inches. The lowest rainfall occurred in 1893 and 

 1894, the precipitation for each of these years being less than 16 inches. 

 Another comparatively dry year occurred in 1907 when the average rain- 

 fall of the whole area was less than 18 inches. This illustrates the great 

 fluctuations in rainfall to which this whole region is occasionally subject. 

 For any single station the fluctuations are much greater. 



Precipitation Not Abnormal. 



"A statement has recently appeared in the Chicago papers to the 

 effect that the rainfall of most of the country west of the 99th meridian 



