24 BULLETIN' 615, IT. S. DEPABTMEBTT OF AGRICULTURE. 



and subsequent decay of the roots; and the addition of humus to the 

 soil by the decomposition of the portions of the plant developed both 

 below and above ground, finally accomplish wonders in improving 

 the physical and chemical condition of the soil, provided, of course, 

 that serious erosion in the meantime has been, checked. 



As the soil is improved and absorbs and retains more water than 

 in the beginning, the annual plants develop more, luxuriantly. At 

 this point, however, the space occupied by the annual species is 

 gradually encroached upon by slightly deeper-rooted, more robust 

 annual plants, usually accompanied by a few shallow-rooted biennial 

 and perennial plants. As the fertility of the soil is further improved, 

 even the more robust annual species disappear and the more perma- 

 nent perennial type of vegetation predominates as formerly. For 

 many years after the latter type becomes conspicuous, how T ever, less 

 forage is produced, and of a poorer quality for stock generally, than 

 before the soil became depleted. 



From the above facts, then, it is evident that soil depletion, as re- 

 lated to forage production and revegetation, does not imply merely 

 a temporary change in the character of the vegetation and. nutritious- 

 ness of the forage ; on the contrary, the time element enters as a 

 highly important consideration. To reestablish completely the more 

 desirable and permanent species, such as occupy the soil before it 

 becomes depleted, often requires years of time coupled with expert 

 management. Too much care can not be exercised by the stockman 

 and farmer in preserving the dark surface layer of soil, for that 

 portion is the very life of any land. Preserving the surface soil in 

 the first place is much cheaper than replacing it, and this is not a 

 difficult matter if proper precautions are taken when incipient 

 erosion becomes apparent. 



INFLUENCE OF GRAZING ON EROSION AND STREAM FLOW. 



While it is evident that the extent of run-off and erosion are 

 roughly proportionate to the effectiveness of the ground cover in 

 binding the soil, other factors being equal, the question as to wdiether 

 run-off and erosion are augmented or retarded by grazing is one upon 

 which opinions vary widely. Some stockmen contend that if a soil 

 is cut up more or less by the trampling of stock, or the surface pretty 

 thoroughly pulverized, more water will be held and subsequently 

 absorbed by the soil than if the surface is undisturbed. Others are of 

 the opposite opinion, contending that the packing of the soil, which 

 unavoidably results from grazing, especially if the soil is fairly moist 

 when stock travel over it, prevents the rain from being absorbed in 

 maximum amounts. In carying out the details of the experiment on 



