Soil Texture in Relation to Rainfall 3 



taining moisture and of permitting it to drain away, 

 and this being true, under one and the same conditions 

 of rainfall one field might be benefited by irrigation 

 while another one would profit by better drainage. 



It is this fact of varying capacity of soils to store 

 water for given periods of time that, in the long strug- 

 gle for existence and of fitting and refitting among 

 plants, has led to the evolution of certain species 

 which can thrive best in a soil of coarse texture, re- 

 taining but small amounts of water for any length of 

 time, while other species have become adapted to the 

 soils of finer texture and higher water capacity. This 

 is a fact of fundamental importance, not only in decid- 

 ing what crops may be grown in a given soil, but 

 whether or not it will be desirable to irrigate such 

 lands beyond the natural rainfall. 



A soil of fine texture is spoken of as the best grass 

 land, for example ; but this has reference, in a very 

 large degree, to a certain amount and frequency of 

 rainfall, which chances to be such as to maintain for 

 the grasses the amount of water in the soil under 

 which they have become accustomed to grow best. If 

 there were another soil in the same locality, of similar 

 composition but of coarser texture, and so of smaller 

 water capacity, it is most probable that this soil would 

 be converted into equally good grass land, giving just 

 as large or even larger yields per acre, if only the 

 natural rainfall were supplemented by artificial irri- 

 gation, so as to hold the water of the soil up to that 

 quantity which the grass has become accustomed, by 

 long breeding, to use. 



