Soluble Salts in Soils. 



93 



105. Maximum Amount of Water Soluble Salts Which 

 Limit Plant Growth. Hilgard concludes from his studies 

 that the maximum amount of soluble alkali salts which are 

 consistent with a full crop of barley hay is 25,000 to 

 32,000 Ibs. per acre in the surface four feet of soil, pro- 

 vided this is not more than one-half its weight sodium car- 

 bonate. 



Whitney places the limit of possible plant production 

 in the soils of the Yellowstone Park at 15,000 Ibs. per 

 acre in the surface foot, where the black alkali or sodium 

 carbonate is absent. 



Grapes grow in Algeria in alkali soils containing 600 

 Ibs. per million of dry soil but die when it reaches 1,700 

 Ibs. per million in the surface soil and 3,700 in the sub- 

 soil ; but grain crops grow normally when the soil contains 

 2,000 Ibs. per million. 



106. Why too Much Soluble Salt in Soil Kills Plants. De 

 Vries found, as represented in Pig. 28, that when the liv- 



4 



FIG. 28. Showing the effect of too strong solution of salts on the proto- 

 plasm of plant cells. 



ing cells of a plant were immersed in a 4 per cent, solution 

 of potassium nitrate, there was first a shrinkage in volume 

 through a loss of water, as shown between 1 and 2. When 

 the solution was given a strength of 6 per cent, the proto- 



