RELATION OF YIELD TO RAINFALL IN THE GREAT PLAINS. 27 



tillage plats; in the seventh column is given the rainfall from April 

 to July, inclusive, in inches. This period is selected as coinciding 

 most nearly with the average growing season at the different stations. 

 The eighth column gives the total rainfall for the year, while the last 

 four columns show the amount that the total rainfall for the year 

 and the season was above or below the normal for that station. 



Referring to the last columns of the table, it will be seen that for 

 the 18 series of experiments reported the rainfall for the year in 9 

 instances was above the normal and in 6 instances below the normal. 

 While the yields in the greater number of cases have been obtained 

 during wet years, very trying conditions were encountered at some 

 of the stations. At Judith Basin, Mont., and at Dickinson, in the 

 western part of North Dakota, the rainfall has been unusually high, 

 ranging from 5 to 10 inches above the normal. The effect of this is 

 well exemplified in the yields at Judith Basin, ordinary methods of 

 cultivation giving as good yields with a bountiful rainfall as either 

 conservation or summer-tillage methods. At Dickinson somewhat 

 higher yields were obtained with summer tillage, but not enough to 

 justify this method if the bountiful rains could have been foreseen. 



At Edgeley, in the southeastern part of North Dakota, three dry 

 seasons were encountered. In the first less than 7 inches of rain fell 

 during the growing season. The yield on spring-plowed land was 4 

 bushels per acre; on summer-fallowed land, 10 bushels. In 1908, 

 with a rain of 9 inches during the growing season, the yields were 13 

 and 16 bushels, respectively; and in 1909, with 11 inches of rain dur- 

 ing the growing season, the yields were 28 and 27 bushels per acre. 

 The effect of a slightly increased rainfall during the growing season 

 upon the yield is very marked at this station. In 1907, with a sea- 

 sonal rainfall of 7 inches, the average yield was about 10 bushels per 

 acre; in 1909, with a seasonal rainfall of 11 inches, the yield was 

 about 29 bushels per acre, or a gain in yield of 19 bushels for an 

 increase in rainfall of 4 inches. 



The results at Edgeley show an increased production on summer- 

 tilled land during 1907, which was very dry. It is important to note, 

 however, that the average yield from the rotation plats was even 

 higher than from the summer-tilled land at this station during this 

 dry year. In fact, the rotations gave better yields than summer- 

 tillage methods for each of the three years during which experiments 

 have been conducted at this station. This indicates that summer 

 tillage is not profitable on the soils of the Edgeley district even during 

 years of deficient rainfall. 



An average yield of about 28 bushels was obtained at the Highmore 

 station in South Dakota during the season of 1907 under a normal 

 rainfall. In 1908 an average yield of 25 bushels per acre was 



188 



