AGRICULTURAL PRACTICE AND CLIMATIC CYCLES. 



265 



summer than in the winter rainfall, and hence more clearly than in the annual 

 rainfall. There is a tendency to maximum rainfall about the sun-spot 

 minimum of 1913, and to minimum rainfall about the sun-spot maximum of 

 1918. However, it is much less decisive at Amarillo than at other places in 

 the Great Plains, indicating the action of a spatial balance in the rainfall of a 

 particular year. The evidence of the excess-deficit cycle of 2 to 3 years is 

 much clearer. From 1908 to 1911 and 1911 to 1914, the cycle was 3 years, 

 while from 1915 to 1916 and 1917 to 1918, it was 2 years. This is reflected in 

 the production, the maximum yields occurring in 1908, 1911, 1915, and 1917. 

 The yield does not correspond with either the annual or seasonal rainfall alone, 

 though it follows the latter more closely. This is due to the fact that while 

 the grains are like the grasses in being chiefly dependent upon the summer 

 rainfall, they also show the effects of a water-content surplus or deficit aris- 

 ing from the year before. There can be little question that the water-content 

 of the soil shows cycles corresponding closely to those of rainfall, and that 

 scientific agriculture must come to take these into account in connection with 

 forecasting the kind of crop and the yield for any particular year. Thus, 

 while the investigation of rainfall and crop cycles presents many complexities, 

 it appears that these are all worked out on the basic pattern of the 22-year, 

 11-year, and 2 to 3 year cycles. If this proves to be the case as the result of 

 intensive studies throughout the West, it is probable that annual crop pro- 

 24 



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1900 1905 1910 1915 



Fig. 17. — Graph of total and seasonal rainfall at Cheyenne, Wyoming. 



