CHAPTER III. 



THE RELATION OF SOILS TO IRRIGATION. 



It was the blind poet Milton who said, "Fame is no 

 plant that grows on mortal soil." He might have add- 

 ed that famous plants are to grow on irrigated soil. 

 The nature, condition and situation of soils compose a 

 most important factor in successful irrigation, and 

 should especially be understood by every person AY ho 

 essays to apply water by artificial methods. In the first 

 place it may be well to understand that primarily soil 

 is rock disintegrated, dissolved or pulverized by the 

 action of the air, water, and ice, aided chemically by the 

 various salts and acids present in the soil, and fertilized 

 by decayed vegetation, animal excretions, and chemical 

 agents. 



Classes of Soils. Nominally there are two dis- 

 tinct classes of soils the sedentary and transported 

 soils, which embrace the drift and alluvial soils. Specif- 

 ically soils are distinctive according to their physical 

 characteristics, and may be classified as gravel, sand, 

 clay, loam, marl, lime, salt, peat, muck or humus. Pure 

 sand consists almost entirely of small grains of silica or 

 quartz and is not a plant food. Plants cannot use it. It 

 is insoluble in water and in acids, and has no adhesive 

 tendency ; hence, acting as a divider in the soil, it 

 makes the land easy to work and facilitates the 

 passage of roots in search of food, and also allows the 

 assimilation of irrigating waters. The amount of sand 

 in the soil varies from eight to more than ninety per 

 cent. It absorbs very little moisture or other fertilizing 



19 



