SOIL AMENDMENTS 349 



bases than acids by plants, but particularly because 

 of the loss of lime and the alkali salts in the drainage 

 water. Acidity may reach a point where it becomes 

 directly injurious to certain plants, but it becomes 

 indirectly injurious before that point is reached. One 

 way in which this occurs is by curtailing the action of 

 certain bacteria in their processes of rendering plant-food 

 available. A slightly alkaline reaction and an easily 

 available base to combine with the organic acids affords 

 the most favorable condition for the decomposition 

 processes due to bacterial action, and hence the best 

 results cannot be obtained where carbonate of lime is not 

 present. Its action in improving tilth also facilitates 

 desirable forms of bacteriological activity by increas- 

 ing the permeability of the soil for air. 



219. Liberation of plant-food materials. It has been 

 stated (page 297) that the alkalies and alkaline earths are 

 more or less interchangeable in certain compounds in 

 the soil. The addition of lime may in this way liberate 

 potassium, when otherwise it would be difficult for 

 crops to obtain a sufficient supply from a particular 

 soil. Magnesium, although rarely deficient, may also 

 be made available in this way. The use of calcium salts 

 may also render phosphorus more useful, probably by 

 supplying a base more soluble than iron or alumina 

 with which in soils deficient in calcium the phosphorus 

 might otherwise be combined. 



Boussingault, as quoted by Storer, found that the 

 addition of lime to a clover crop increased greatly the 

 calcium, potassium and phosphorus contained in the 

 crop. 



