31 



to be suffering from drought; the leaves will be yellowish and th* 

 stalks stunted. 



COMPOSITION OF ALKALI. 



Iii an alkali crust the compounds usually predominating are, so- 

 dium carbonate, sodium sulphate, sodium chloride, and compounds of 

 calcium and magnesium. There are three types of alkali soils, the 

 white, characterized by an excess of sodium sulphate; the black, by 

 an excess of sodium carbonate; and the salt, by an excess of sodium 

 chloride or common salt. Either of the three may contain all of the 

 compounds. 



The black alkali is by far the most disastrous to plant growth and 

 the most difficult to handle. It is produced by the change of certain 

 sodium compounds such as sodium sulphate (white alkali) into sodium 

 carbonate. It is commonly called sal soda; it turns red litmus to blue, 

 and burns \f taken into the mouth. The dark color of the soils con- 

 taining it is due to its combination with organic matter; existing 

 alone, it is white. 



EFFECTS OF ALKALI ON THE CHEMICAL COMPOSITION AND PHYSICAL 

 PROPERTIES OF SOIL. 



Where moisture is present, the alkali salts (including calcium salts) 

 aid in the important work of decomposing organic material. This 

 decomposed material in turn, will combine with some of the alkalies 

 to form new compounds which would otherwise be unavailable for 



One feature of their labors is of particular interest the Huacas or mounds. Through- 

 out many of the valleys may be seen piles of earth varying in size from small knolls to 

 huge mounds 60 or 70 feet high and sometimes covering an area of one or two acres. 

 There seem to be two types of mounds; those made of adobes (usually the larger 

 mounds) piled one upon another and carefully cemented with mud, and thost that are 

 merely piles of earth. Those of the latter type may have originated through the efforts 

 of the farmers to protect their crops by scraping up the alkali and throwing it into piles. 

 The soils of these piles will often be found to be of the same character as the soils sur- 

 rounding and to contain a considerable amount|of the alkali of that section-in some cases, 

 as much as 1.33 n \^ water soluble chlorides, and 2.85 [ water soluble sulphates. 



There are various theories as to why these Huacas were constructed. They may have 

 been temples, lookouts, or protections against enemies. Some of them were assured'y 

 burying places and not only are bones found in them, but pieces of pottery, household 

 utensils and trinkets, for the dead had personal belongings buried with them, and food 

 and clrink for use when making the "Long journey". 



