SOILS AND FERTILIZERS 343 



grain on account of the general occurence of hardpan and very stiff 

 and impervious subsoils. Recently in the Sacramento area some 

 members of this series have been very successfully used for the 

 production of the Tokay grape and strawberries: 



Sierra Series. Light-gray to red and frequently gravelly soils, 

 often underlain by red adobe. Members of this series constitute 

 some of the most valuable deciduous fruit soils of the foothills in 

 northern California. 



Sites Series. Residual and colluvial soils of reddish-gray or 

 dark-brown color, derived from sandstones, shales, conglomerates, 

 and volcanic or altered material occupying low rolling foothills 

 and their valley slopes, usually underlain at shallow depths by 

 sandstones, conglomerates, or heavy subsoils. The Sites loam and 

 clay loam adobe are the important soils of this series and are pro- 

 ductive, but owing to their position are generally unirrigable and 

 adapted to dry farming to grains. 



Stockton Series. Brown to black soils with heavy yellow sub- 

 soils, derived from old alluvial sediments. These soils have been 

 used principally for the production of grain. The lighter members 

 of this series have been adapted to fruit. 



Willows Series. Brown soils consisting of wash deposited by 

 intermittent foothill streams. These soils have been used almost 

 exclusively for dry farming grain crops. Large ranches are being 

 broken up and brought under irrigation, and alfalfa and sugar 

 beete are likely to prove the most important crops. ] 



ALKALI SOILS. 



The climate of arid regions is directly responsible for the prev- 

 alence of sandy soils containing large stores of water-soluble mate- 

 rials, which at once become productive upon the application of water. 

 Even the most desolate stretches of desert will supply good crops if 

 the needed water is applied, as is shown by the millions of acres of 

 land now under cultivation that were formerly a barren desert. 

 While this is generally the case there are a few exceptions, one of 

 the most striking of which is when the soil contains alkali. Fre- 

 quently alkali does not appear in an irrigated district until cultiva- 

 tion has been practiced for a number of years. The substances com- 

 posing the alkali may be present in the soil before the application of 

 water, or they may be brought in by the irrigation waters. In hot, 

 dry weather, after rains or irrigation, the alkali frequently appears 

 on the surface of the soil as a white crust. 



Alkali consists of various chemical compounds (salts) which 

 are often present in western soils in sufficient quantity to hinder or 

 prevent the growth of plants. Most of these salts are familiar to 

 everyone from their medicinal or household uses. The most common 

 of these substances are Glauber's salt (sodium sulphate), table salt 

 (sodium chlorid), and 'baking soda (sodium bicarbonate). The so- 

 called black alkali is sal soda, or washing soda (sodium carbonate) . 

 Epsom salts (magnesium sulphate) is also an important ingredient of 

 alkali in certain localities. All of these salts readily dissolve in water. 

 Less soluble compounds that often occur in alkali soils are the car- 



