36 



IRRIGATION AND ALKALI LANDS.* 



In many portions of the world, and oftenest in arid and semi-arid 

 regions, the waters of some streams and wells, and particular.y those 

 of lakes, are too heavily charged with the salts of sodium — common 

 salt, sal soda and Glauber's salt or sodium chloride, carbonate and 

 sulphate respectively — to make it advisable to use them for the pur- 

 poses of irrigation. These salts are a part of the waste products of 

 soil production which ordinary vegetation is unable to use with profit, 

 and which in countries of heavy rainfall are washed out of the soil 

 nearly as rapidly as formed. "Where these salts, however, do accumu- 

 late to any notable extent, it is designated an alkali soil, and will not 

 produce normal crops of many of the forms grown in plant husbandry. . . 



CHARACTERISTICS OF ALKALI LANDS. 



The use of the term "alkali lands" as commonly employed, has 

 quite a loose or wide application. Hilgard states that in California 

 the term is applied almost indiscriminately to all lands whose soils 

 contain unusual amounts of soluble salts, so that during the dry season 

 or after irrigation the surface becomes more or less white with the 

 deposits left by the evaporation of the capillary waters. . . Where 

 these salts are well marked in character, crops are killed out entirely, 

 or the growth is stunted much as is true of the black alkali spots of 

 arid regions. On the rice fields of South Carolina, there appear dur- 

 ing the dry stage of growth of the crop " alum spots," as they are 

 called, upon which the rice may die out or be of inferior quality. 

 Then, too, on the margins of the sea, where there are low lying lands 

 periodically inundated by high tides, white deposits are again left when 

 the surface becomes dry, and are injurious to cultivated crops when 

 they have accumulated to sufficient strength, and these are sometimes 

 spoken of as " alkali lands." 



In the wide application of the term, then, " alkali lands" are those 

 upon which soluble salts have accumulated in sufficient quantity, 

 through evaporation and capillarity, to attract attention by their 

 usually white appearance and their injurious effects upon vegeta- 

 tion. . 



CAUSE OF INJURIES BY ALKALIES. 



When the soil water about the roots of plants or germinating seeds 

 becomes sufficiently strong with salts in solution, the osmotic pressure 

 is so modified that a discharge of the cell contents into the soil takes 

 place to such an extent as to produce what is equivalent to wilting. 

 The cells are not maintained sufficiently turgid to permit normal 

 growth, or they may have the pressure so much lowered as to cause 

 death. The case is like placing the plump strawberry or currant in^ a 

 strong solution of sugar, where it is observed to greatly shrink in 

 volume. . . . iMtfl 



This, then, is one of the modes by which the injurious effects'of 

 alkalies are produced, and it should be understood that it matters very 

 little what substance may be in solution in the soil water, so long as it 

 is there in sufficient quantity to produce the osmotic shrinkage re- 

 ferred to. 



* From " Irrigation and Drainage" by Prof. T. H. King, published by McMillan 

 London and New-Ycrk. 



