Dec, 1909.] POTASH IN CLAY LOAM SOILS. 57 



large quantities of mineral plant food, as well as the nitrogen, 

 are made available. "When potassium salts are once absorbed 

 by the organic matter, they are washed out with water only very 

 slowly. After rains the evaporation carries away more water 

 clay is the same. Because of the oxidation which breaks up 

 the organic matter, the plant food there ought to be more avail- 

 able than that which is absorbed in the clay. 



SOME EFFECTS OF AIR-SLAKED OR CARBONATE OF 



LIME. 



We have already seen how an ordinary soil acts on chloride of 

 potassium to make the potassium insoluble. At the same time 

 other interesting changes take place. While the potassium goes 

 out of solution, certain other bases, including lime, iron and 

 aluminum, go into solution. In other words, the potassium ex- 

 changes places with these bases and becomes insoluble, while 

 they become soluble. Laboratory experiments show that the 

 nature of the soil determines what new bases become soluble 

 under such conditions. If a soil poor in lime is treated with 

 potassium chloride, relatively large amounts of iron and alumi- 

 num become soluble. On the other hand, if the soil is rich in 

 lime, almost no iron or aluminum dissolves, but a large quantity 

 of lime goes into solution. This difference is of much practical 

 importance. If a soil forms soluble iron and aluminum when 

 treated with chloride of potassium or sulfate of ammonia, it is 

 likely to produce harmful instead of helpful results. Aside 

 from the deleterious effects of these bases, hydrolysis causes the 

 formation of free acids, which are also harmful. The applica- 

 tion of lime to such soils prevents the solubility of the iron and 

 aluminum, and also the formation of acid conditions. 



It has been noted that when sulfate of ammonia was applied 

 to certain soils^ acid conditions were established which caused a 

 very poor crop yield. This condition was found to be changed 

 by application of lime along with the ammonium sulfate. While 

 no soluble iron was detected in these soils, it is quite possible 

 that a part of the trouble was caused in this way. The lime 

 would remove any soluble iron and aluminum and at the same 

 time lime and its salts exert a very marked influence upon plant 

 growth and particularly upon the root systems. 



iWheeler Rhode Island Station Report, p. 212, 1893. 



