3Ia2^2^ing Soils and Alkali 



37 



These results so obtained are the cubic centimeters of N/10 sohi- 

 tion of sodium carbonate corresponding to the hmiting vahies, to 



be inserted in the following table: 



If it is desired to reduce the volume of X; 10 AgNO^ to per cent 

 of NaCl in dry soil, the following formula may be used: 



Y 0.005806 



Substituting 0.004172 for 0.005806, the same formula may be used 

 to reduce the volume of N/20 HKSO^ to per cent of NaHCOs- 

 Y=cubic centimeters N/IO AgXOg or N/20 HKSOi solution used; 

 Y^= volume saturated soil represented in amount of solution 

 titrated; K=constant for type of soil as follows: 



s. and ssc.=1.46; sc.=1.32; sec. =1.26; c. and he. =1.21. 



Construction of alkali maps. — The directions for n>apping alkali 

 soils in the field, just given, which are also to be found in the front 

 of the Alkali Field Book, will enable you to determine the per- 

 centage of alkali in any sample of soil. It has been the practice 

 of this Bureau to prepare maps showing the percentage of alkali 

 in the surface 6 feet of soil. This has generally been considered 

 to be a mathematical average of the salt content of the 6 feet; but 

 in nearly all cases the judgment cf the person in charge of the 

 work as to the actual crop value of the soil on the basis of alfalfa 

 has entered into the construction of the maps. 



To do away as much. as possible with this element of judgment 

 and to place the construction of the maps entirely upon a percent- 

 age basis — that they may be of equal value when any crop is con- 

 sidered — and to permit the strict comparison of the work done by 

 different men, the following plan is to be adopted: 



The percentage of alkali salts in each foot of land to a depth of 



