RELATION OF YIELD TO RAINFALL IN THE GREAT PLAINS. 25 



adapted to such conditions and is the method uniformly followed in 

 that part of the Columbia Basin where the rainfall is light. Summer 

 tillage of the fallow land is also carried on quite generally throughout 

 the region. a The rainfall records in the drier portions of the Columbia 

 Basin are very broken, so that it is not possible at the present time 

 to determine the relation of yield to rainfall with exactness. 

 Hunter, 6 who has made a special study of the conditions in this 

 region, states that while wheat is being produced on an average annual 

 rainfall as low as 8.5 inches, 10 inches is about the minimum for suc- 

 cessful wheat production. A great deal of wheat is grown around 

 Ella, in Morrow County, Oregon, and in other parts of the northern 

 tier of counties in Oregon where the rainfall is no greater than that 

 of Ella. The average annual precipitation at Ella, Oreg., during the 

 last ten years has been 9.5 inches. During this period the rainfall 

 has varied from 12.8 inches in 1906 to 5.2 in 1908. During a year 

 of heavy rainfall the yield of the wheat crop grown on summer- 

 fallowed land at Ella is from 20 to 30 bushels per acre, or even more. 

 When the rainfall is 6 or 7 inches the crop is sometimes not worth 

 cutting and the yields are frequently only 6 or 7 bushels per acre. 

 No wheat is grown in the driest part of the basin in the vicinity of 

 Pasco, Wash., where the annual rainfall is only about 6 inches. 



It appears to be established, then, that wheat is being grown at 

 a profit in this region by summer-fallowing methods on an annual 

 rainfall of 10 inches. The minimum rainfall necessary for a wheat 

 crop that will return more than the cost of production appears to be 

 about 8.5 inches, although actual yields in connection with rainfall 

 records are not yet available to establish this minimum definitely. 

 The yields on the same rainfall of course vary considerably according 

 to the methods and care employed in the production of the crop. 



RELATION OF YIELD TO RAINFALL IN THE GREAT PLAINS. 



The Office of Dry-Land Agriculture Investigations of the Bureau of 

 Plant Industry has been conducting extensive investigations since 

 1906 to determine the cultural methods and systems of crop rotation 

 best adapted to the conditions in the Great Plains. The following 

 table has been compiled from the results of these experiments, which 

 are now available to the end of the season of 1909. c The results of the 



a For a description of the methods of tillage used in this section, see the paper by 

 Byron Hunter, entitled "Farm Practice in the Columbia Basin Uplands," Farmers' 

 Bulletin 294, U. S. Dept. of Agriculture, 1907. 



& The writers desire to acknowledge their indebtedness to Mr. Byron Hunter, of the 

 Office of Farm Management of the Bureau of Plant Industry, for the information 

 relative to wheat yields in the Columbia Basin. 



c See "A Study of Cultivation Methods and Crop Rotations for the Great Plains 

 Area," by E. C. Chilcott and members of the field staff of Dry-Land Agriculture Inves- 

 tigations, Bulletin 187, Bureau of Plant Industry, U. S. Dept. of Agriculture, 1910. 

 188 



