LIMING THE SOIL 373 



crops. The possible influences of lime on plants may be listed 

 as follows: (1) direct nntritive action; (2) synergistic rela- 

 tionships either in the soil solution or in the cell-wall; (3) re- 

 moval or neutralization of toxins of either an organic or inor- 

 ganic nature; (4) effect on plant diseases; (5) liberation of 

 mineral nutrients; and (6) encouragement of the biological 

 preparation of nutrient materials. 



In some cases the calcium may function as a direct nutrient ; 

 in others the intake of nutrients may be facilitated by the 

 presence of calcium and magnesium; while in still other cases 

 the elimination or alleviation of a toxic condition may be the 

 important result. It is easy to conceive that any two or all 

 three of these relationships might be fulfilled simultaneously 

 by lime. The stimulating influence of lime might also make 

 the plant a more active agent and thus encourage it to aid 

 to a greater extent in the preparation of its own nutrients. 

 Certain diseases may be retarded or even entirely suppressed 

 by lime, as is the **finger-and-toe" disease of the Cruciferse. 



The liberation of mineral nutrients, such as potash and 

 phosphoric acid, by the addition of lime, is somewhat uncer- 

 tain although it evidently does occur in many cases.^ The 

 process is probably a more or less complicated physical or 

 chemical change. The stimulation to plants by such an ac- 

 tion is difficult to establish, since so many disturbing factors 

 are active in obscuring the results. Lime is undoubtedly very 

 important in the use of acid phosphate, the active compound 

 of which is mono-calcium phosphate (CaH4(P04)2). In the 

 presence of active calcium, the reversion compound is 

 (Ca3(P04)2),^ rather than the very insoluble iron and alumi- 

 num phosphates (FePO^ and AIPO4). 



The formation of nitrates proceeds rather slowly in most 



^Plummer, J. K., The Effects of Liming on the Availability of Soil 

 Potassium, Phosphorus and Sulfur; Jour. Amer. Soc. Agron., Yol. 13, 

 No. 4, pp. 162-171, 1921. 



^GaH^CPOO, + 2CaH,(C03), = Ca«(P04)s + ^H^O + 400, 



