178 CONTROL OF EROSION ON RANGE AND PASTURE 



Type of Soil. — The character of the soil itself often de- 

 termines to a considerable extent the degree of erosion. The 

 factors determining the extent to which a given soil type may 

 erode are texture, structure, amount of organic matter, pore 

 space, and tenacity. 



Texture. — Coarse-textured soils, that is, those having large- 

 sized particles like sand, are able to absorb a large amount of 

 rainfall. Accordingly, little water, except on very steep slopes, 

 washes over the surface of such lands, and hence serious erosion 

 seldom occurs. Soils like clay that have small-sized par- 

 ticles hold much less fallen rain than do soils of coarse tex- 

 ture. 



Structure. — The particular arrangement of the particles of 

 soil greatly influences the amount of water which is absorbed. 

 When the particles are pressed closely together, as in heavily 

 packed soils, the spaces between the particles are so small that 

 water can be absorbed but slowly. Thus a large portion of the 

 water is carried over the surface of the soil and causes erosion. 

 The structure of any soil is greatly modified by the amount of 

 vegetation which occurs upon it, and, to be sure, by the type 

 of farm operation. 



Organic Matter. — Organic matter invariably increases the 

 power of soils to absorb and retain moisture. Accordingly, the 

 amount of organic matter plays an important part in the pre- 

 vention of erosion both of heavy and of light soils. 



Pore Space. — The amount of pore space and the size of the 

 individual pore spaces have an important part in determining 

 the amount of water taken up by a soil and the rate at which it 

 is absorbed. Both the amount of water absorbed and the rate 

 of its absorption are affected by the size of the particles, their 

 arrangement, and the amount of organic matter present. 



Tenacity. — The rate at which the stickiness or maximum 

 tenacity of a soO is reached determines to a considerable extent 

 the erosion that may take place. The amount of organic matter, 

 the degree of compactness, and the particular type of soil greatly 

 influence the ability of a soil to absorb moisture, and hence the 

 extent to which the soil may erode. Any method of building 



