15 



found in them. The most common of these salts is sodium chloride, but 

 besides this we may find, and often do find, the chlorides of calcium, potas- 

 sium and magnesium, and the sulfates, bicarbonates and carbonates of 

 these four metals. AVe hardly ever find only one salt present in any one 

 soil, but usually most or all of them in varying proportions. 



Most cultivated plants are unable to grow in soils that are heavily 

 charged with salts. The injury produced is due to direct as well as 

 indirect causes. There is a direct corrosive action on the roots; and 

 there are also produced, through the salts that are taken up by the plant, 

 certain disturbances of the natural biological processes. Among the 

 indirect effects of alkali one of the most important probably is that on 

 nitrificalioji. Lipman (*) has found that nitrification does not proceed 

 normally when the concentration of sodium carbonate in the soil reach.es 

 0.025%. Sodium chloride is less toxic, and nitrification is quite normal 

 up to a concentration of 0.1 r ; of this salt, while the quantity of sodium 

 sulfate may reach even 0.35% without ill effects. The effect of salts 

 on a rnmonifieation is of a different order, sodium chloride being the 

 most toxic and sodium carbonate the least. These results are most 

 important and they may partly explain the favorable effect of lime 

 salts in salt lands. They counteract the influence of the other salts with 

 the result that nitrification may proceed normally, which it could not 

 do in the presence of the other salts by themselves. 



If it is intended to use salt lands for agricultural purposes, the salts 

 must be partly or wholly removed. In some cases certain measures will 

 produce a considerable improvement, for instance the application of 

 calcium sulfate which counteracts the effects of other salts and converts 

 sodium carbonate into the less toxic sulfate, under the formation, at the 

 same time, of insoluble calcium carbonate. But such measures as these 

 will be effective in rare cases only. There is only one method which will 

 absolutely and permanently reclaim the better of these lands, and this is 

 an efficient system of drainage in connection with irrigation to leach out 

 the salts. 



There exist great differences in the tolerance of plants for different 

 salts, and in that of different plants for the same salt. The limits of salt 

 content also vary with the character of the soil. In general it may be 

 said that sodium carbonate is the most toxic of all salts; the upper 

 limit tolerated, for instance, by cereals in a sandy loam soil, is about 

 0.1 % ; sodium chloride, sodium bicarbonate and magnesium chloride are 

 less toxic, and the maximum for sodium chloride is, under the above 

 conditions, 0.25%. Sodium sulfate and magnesium sulfate are still less 

 harmful than the former, the limit of sodium sulfate being about 0.45 

 to 0.5% (1). Calcium salts are the least toxic of all and rather large 



(1) Centr. Bakt. Parasitenk.. IT. Abt., Vol. 33, pp. 305-313. 

 ~W Hilgard, "Soils", p. 464. 



