396 SOILS. 



stances to be supplied by fertilization when production lan- 

 guishes, in the arid regions it will as rule come last in order 

 among the three ingredients commonly so furnished. Aside 

 from the water-soluble potash salts always forming part of 

 the salts of the alkali lands proper, which in many cases will 

 alone hold out for many years under the demands of cultiva- 

 tion, 1 they rarely contain much less than one per cent, of acid- 

 soluble potash; occasionally rising as high as 1.8 per cent. 

 That in such lands potash-fertilization is uncalled-for and in- 

 effective, hardly requires discussion ; while on the other hand, 

 phosphates are commonly required for full production after 

 ten or fifteen years of cultivation without returns. Nitrogen 

 usually comes next in order, but sometimes is the first need. 



The constant indiscriminate purchase and use of all three ingredients, 

 so urgently recommended by fertilizer manufacturers because of their 

 success in the humid Eastern States, is therefore very poor economy for 

 the farmers of the arid region. Excepting cases of very intense culture, 

 e.g. of vegetables or berries, the use of potash salts is but rarely remuner- 

 ative, and therefore uncalled-for, in arid soils for a number of years. 



Humus. The figures shown in the table for the average 

 humus-percentages in the soils of the two regions do not ade- 

 quately represent the very important differences actually ex- 

 isting; partly because of the inadequate number of determina- 

 tions made by the same method (Grandeau's), partly because 

 of the differences in the composition, and especially in the 

 nitrogen-content of this substance, which render direct com- 

 parison delusive. A detailed discussion of the marked differ- 

 ences existing between the humus of arid and humid soils in 

 this respect has already been given (chapter 8, p. 135) ; show- 

 ing that the high nitrogen-percentage in the arid humus prob- 

 ably compensates largely the lower humus-percentage, while 

 rendering nitrification more rapid, because the oxygen is not 

 consumed by overwhelming amounts of carbon and hydrogen ; 

 which, as is already known, take precedence of nitrogen in the 

 oxidation of humus substances. Nitrates are almost always 



1 In the light alkali lands of the southern California Experiment Substation at 

 Chino, the average content of water-soluble potash in ten acres amounts to the 

 equivalent of 1,200 pounds of potash sulphate per acre. Outside of this the acid- 

 soluble potash of the soil is .95 ., equal to 38,00x3 pounds per acre-foot. 



