EFFECTS OF DIFFERENT SYSTEMS OF GRAZING. 19 



greatest total gain p^r pasture and per acre will be obtained. While 

 the maximum gains per head or per acre may not be the most 

 desirable measure of grazing efficiency, they are essential within 

 certain limits. It is obvious that the number of cattle may be in- 

 creased until the total gain secured is greater than for any other 

 system of grazing. However, this may be carried to a point where 

 the gains per head may be so reduced that 25 cattle will produce no 

 greater total gain than that produced by 20 head on the same acre- 

 age under the same system of grazing. 



The measure of grazing efficiency as formulated is not as difficult 

 of attainment as might at first appear. In order to provide the 

 greatest total gain per unit area, the native forage must be allowed 

 to maintain its maximum power of production. Continual close 

 grazing early in the season causes a reduced production of forage. 

 Therefore, the vegetation must have a period of rest and be allowed 

 to mature a crop normally before it is grazed. In order to avoid 

 too greatly reducing the gains per head of the cattle by forcing 

 them to graze a short pasture for a long period, they must be allowed 

 to graze different units for shorter periods. Such a system of grazing 

 will also insure the maximum utilization of the vegetation with 

 the least injury to it. The deferred and rotation system of grazing 

 will come nearer to fulfilling the requirements of the measure of 

 grazing efficiency than continuous grazing on a larger or smaller 

 acreage per head. 



BOTANICAL STUDIES IN CONNECTION WITH THE EXPERIMENT. 



The first step necessary in connection with this experiment was a 

 complete survey of the native vegetation. Therefore, in 1915 an 

 herbarium was collected, comprising between 275 and 300 species 

 of plants. This has been enlarged during the succeeding years. The 

 plants collected are practically all confined to the highlands or 

 prairie. Of the total number of species from 50 to 60 are grasses. 

 AVhile a comparatively large number of species of plants grow on 

 the prairie, only 25 or 30 are important from the standpoint of 

 grazing. 12 Out of this number four species produce approximately 

 half of the forage. 



It was not only necessary to know the individual species of plants, 

 but also to determine their relationship to each other. This phase 

 of the work has been more fully discussed elsewhere. 13 



The vegetation of this section is not as complex as that in some 

 other parts of the Great Plains; for example, at Ardmore, S. Dak. 

 The composition of the vegetation is remarkably uniform throughout 

 the area. This fact tends to minimize complications in recording 

 the effects of grazing. 



The composition of the vegetation is very clearly illustrated in 

 Plate II, Figure 1. The season of 1915, when the photograph shown 

 in this illustration was taken, was very favorable, and all plants 

 reached their maximum development. 



13 Sampson. Arthur W. Important range plants: Their life history and forage value. 

 U. S. Dept. Agr. Bui. 545, 63 pp., 56 pis. 1917. 



13 Sarvis, J. T. Composition and density of the native vegetation in the vicinity of 

 the Northern Great Plains Field Station. In Jour. Agr. Research, v. 19, pp. 63-72, 

 2 figs., pis. 12-14. 1920. 



