244 JUDGING ALKALI LAND 



should be analyzed depends on a number of factors. Four 

 and o feet are often taken as standards but 10 feet is 

 better. At least an occasional sample should be taken to 

 this depth to see that in the deep subsoil there is not a 

 layer of high concentration that will cause trouble later. 



The exact determinations to be made will depend on 

 the thoroughness of the investigation desired. A complete 

 chemical analysis of all the water-soluble material would 

 be desirable, but a fair idea can be had with much less 

 work. An absolutely necessary determination to any sort 

 of intelligent diagnosis would include total soluble salts, 

 chlorides, carbonates, and sulphates. In comparatively 

 few regions where nitrates are high, they should also be 

 determined. Where any large part of the sulphates are 

 calcium sulphate, calcium should be determined in order 

 that the calcium sulphate may be subtracted from the total 

 soluble salts and the sulphates. Calcium sulphate is not 

 sufficiently soluble in the soil solution to be toxic to vege- 

 tation, but where comparatively large quantities of water 

 are used in extracting the soil for analysis, considerable 

 calcium sulphate is contained in the solution, and where it 

 forms any large part of the dissolved material it should be 

 taken into consideration. It is also desirable to have 

 determinations made of other bases such as magnesium 

 and sodium, but these determinations are not so valuable 

 as the others that have been mentioned. 



The methods of analysis, particularly the method of 

 making extractions, must be taken into consideration in 

 interpreting the results. Different methods give different 

 results; consequently the methods should always be known. 

 Details of the various methods are given in Chapter VII. 



Possibility of Reclamation. The value of alkali land 

 is affected very materially by the possibility and the ex- 



