RANGE IMPROVEMENT. 



313 



sible to check the assumed optimum carrying capacity by rates of grazing 

 which reveal both over- and under-utilization, and in demonstrating the 

 additional gain resulting from rotation methods. Installations for the inten- 

 sive study of carrying capacity and rotation grazing have been made by the 

 Office of Dry-Land Agriculture at Mandan and at Ardmore. Both are 

 located in the mixed prairie, the one in Stipa-Bouteloua, and the other in 

 Bulbilis-Agropyrum-Bouteloua. Since the methods are essentially alike, it 

 will suffice to describe briefly the experiments at Mandan, which have been 

 under way since 1915. 



Reserve pasture 

 (70 acres) 



K 



164 acres 



30 acres 



Q 

 70 acres 



70 A. rotation 



70 acres 



Scale in feet 



500 



Fig. 22. — Pastures for the intensive study of carrying capacity and rotation 

 grazing, Mandan, North Dakota. After Sarvis. 



There are four pastures for the investigation of carrying capacity under 

 continuous grazing, two for rotation grazing, a reserve pasture, and one for 

 the study of hay development (fig. 22). At Ardmore two pastures are de- 

 voted to continuous grazing and the same number to rotation. The four 

 pastures contain respectively 30, 50, 70, and 100 acres. Since each pasture 

 is grazed by 10 two-year-old steers, the corresponding rates of grazing are 

 1:3, 1:5, 1:7, and 1 : 10. Each pasture contains an exclosure termed an 

 isolation transect (fig. 23), which is 300 feet long and 60 feet wide. This con- 

 sists of three strips, of which the central one, P, serves as permanent transect 

 for annual comparison with the grazing and regeneration transects on either 

 side, as well as for the installation of permanent quadrats of various types. 

 One unit of the grazing transect, G, is unfenced for each year of the climatic 

 cycle, while one of the regeneration transect, R, is fenced for each successive 



