390 IRRIGATION PRACTICE 



On the soils derived from many of these deposits, plant- 

 growth is difficult or impossible, and they are therefore 

 easily recognized. 



Water passing through these alkali deposits of early 

 times and dissolving the salts, carries alkali to otherwise 

 alkali-free sections. This is a chief source of alkali, next 

 in importance to over-irrigation, although it has been 

 largely overlooked by students of alkali. Knight and 

 Slosson, of Wyoming, have shown that great numbers of 

 such deposits occur in Wyoming; other students of 

 western conditions have discovered similar deposits in 

 various districts; and Stewart and Peterson, of Utah, 

 have recently confirmed the wide distribution of such 

 alkali deposits. Once the existence of such deposits is 

 recognized in the neighborhood, precautions against them 

 may be taken, and they need not then be a menace. 

 (Fig. 114.) 



234. Kinds of alkali. Since alkali is simply the 

 soluble matter of soils accumulated to an injurious degree, 

 it follows that alkali may contain any or all of the con- 

 stituents of rocks and soils. The numerous existing analy- 

 ses show that in alkali there is a preponderance of the 

 bases, sodium, calcium and magnesium, combined with 

 hydrochloric, sulfuric, carbonic and nitric acids. In 

 other words, the chlorides, sulfates, carbonates and 

 nitrates of sodium, calcium and magnesium are the chief 

 constituents of ordinary alkali. In addition to these 

 dominant constituents there are a great many others, as 

 potassium salts, phosphates and other indispensable 

 plant-foods. Alkali may be said to be the cream of soil 

 fertility, so concentrated as to cause plant indigestion. 

 The following table gives partial analyses of four samples 

 of alkali crust: 



