EFFECTS OF DIFFERENT SYSTEMS OF GRAZING. 7 



restoration process. The depletion or destruction of the native vege- 

 tation by overgrazing with cattle does not occur suddenly; 6 it is 

 cumulative, and an overgrazed pasture may continue to produce a 

 limited quantity of feed for a number of years. 



RELATION OF PRECIPITATION TO NATIVE FORAGE PRODUCTION. 



The amount of precipitation during April and May exerts a 

 greater influence upon the annual production of native forage than 

 upon the production of small-grain crops during the same season. 

 A normal rainfall during the early season practically insures a rea- 

 sonable growth of native forage, even though the later rainfall is 

 belcw normal. Such a condition ma}' mean a very light crop or 

 the failure of the small grains. This point was well illustrated dur- 

 ing 1921. The rainfall during April and May was above normal, 

 while during June and until the last week in July it was much be- 

 low normal. As a result the native forage produced more than in 

 1920, while the small grains were decidedly reduced in yield. 



The mean annual precipitation for the 45-year period from 1875 

 to 1919, inclusive, was 17.17 inches. 7 The mean seasonal precipita- 

 tion from April 1 to August 31, inclusive, was 11.84 inches during 

 the same period. The month of maximum precipitation is June, 

 with a mean of 3.51 inches for the 45-year period. 



Table 1. — Annual precipitation vcar Mandan, N. Dak., by months, for the 

 6-year period pom 1016 to 1921, inclusive. 





















Sea- 





Year. 



Jan. 



Feb. 



Mar. 



Apr. 



May. June. July. Aug. Sept. 



Oct. 



Nov. 



Dec. 



sonal, 

 Apr. 



An- 

 nual. 























-Aug. 





1916 



.. 0.28 



0.09 



1.88 



0.93 



1. 69 2. 25 



3. 55 2. 04 0. 92 



0.27 



0.07 



1.10 



10.46 



15.07 



1917 



.. .28 



.19 



.35 



1.87 



.35 2.56 1.58 .89 1.97 



.05 



.03 



.19 7.25 '10.31 



1918 



.. .20 



.11 



.45 



2.61 



2.45 .68 2.47 2. 03 .63 



.27 



.45 



1.02 10.24 13.37 



1919 



.. .08 



.80 



.83 



1.72 



3.95 1.12 .85 1.22 .49 



.98 



1.19 



. 25 8. 86 13. 48 



1920 



.. .52 



.20 



1.21 



.58 



1.72 1.85 2.68 1.81 1.29 



.25 



.37 



.21 8. 64 12. 69 



1921 



.. .18 



.09 



.79 



2. 59 J 3. 05 . 82 3. 38 . 25 1. 58 



1.39 



.87 



.24 10.09 15.23 



Mean 



.. .26 



.25 



.92 



1.72 



2.20 j 1.55 



2. 42 1. 37 



1.15 



.54 



.50 



.50 9. 26 



13.36 



1 Lowest during 47 years. 



TThile the grazing experiment has been in progress it has passed 

 through the driest series of years that have obtained in this section 

 during the period of record. The driest consecutive six years pre- 

 vious to 1916 was from 1885 to 1890, inclusive, with an annual mean 

 precipitation of 14.33 inches. The mean seasonal precipitation from 

 April 1 to August 31, inclusive, for the same period was 10.05 inches. 

 Table 1 shows the annual precipitation by months for the six-year 

 period from 1916 to 1921, inclusive, i. e., during the period covered 

 by the grazing experiment. The annual precipitation of these six 

 years ranged from 10.31 to 15.23 inches and averaged 13.36 inches. 

 The seasonal precipitation from April 1 to August 31, inclusive, for 

 the same period averaged 9.26 inches. 



6 Wilcox, E. V. The grazing industry. Hawaii Agr. Exp. Sta., 91 pp. 1911. Bibli- 

 ographical footnotes. 



7 Data based upon the records of the United States Weather Bureau at Bismarck, 

 N. Dak., and those recorded since 1914 at the Northern Great Plains Eield Station, 

 Mandan, N. Dak. 



