448 SOILS. 



in soils by the formation of complex zeolitic silicates. In most cases 

 the potash-percentage exceeds .75%, and rises as high as 2.0^ ; as is 

 shown in the table. 



This table exhibits also another standing characteristic of 

 alkali soils, which is to be anticipated from the conditions of 

 their formation ; viz, high lime-content, which sometimes rises 

 to the extent of marliness. 



In phosphates, also, alkali soils are almost always high ; and 

 an unusually large proportion is found to be readily soluble. 



In presence of much carbonate of soda, nitrates are usually 

 scarce or altogether absent; while owing to the action of the 

 alkaline solution upon the humus, ammonia salts, or even free 

 (or carbonated and therefore readily dissociated and assimi- 

 lated) ammonia may be present, so as to be perceptible to the 

 senses by its odor in hot sunshine. But in the case of " white 

 alkali," more especially of the sulphate in moderate amounts, 

 nitrification is exceedingly active and nitrates may sometimes 

 rise to as much as 20% of the soluble salts. As alkali spots are 

 usually low in the central portion and therefore more moist 

 than around the edges, we sometimes find ammonia salts in the 

 middle of a spot, while nitrates are abundant along the mar- 

 gin of the same. These differences, first demonstrated by an 

 investigation made by Colmore, 1 illustrate some of the reac- 

 tions that are essentially concerned in the agricultural avail- 

 ability of alkali lands. A summary of Colmore's results is 

 given in the table below. 



Cross Section of an Alkali Spot. The spot examined lies 

 outside of Tulare, California, substation; it being late in the 

 season, when the bulk of the salts is found near the surface, 

 the samples were taken to the depth of one foot only, at points 

 four feet apart, from the center out. 



1 Report of the California Exp't St'n for 1892-94, p. 141. 



