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The chemical and biological effects of the action of lime on soils 

 are closely connected, since the biological effects are productive of 

 changes in the chemical compounds present in the soil. 



These effects are general, to a greater or less extent, for all types 

 of soil. 



/. Mechanical effects of lime on soils. — The first of these has been 

 sufficiently dealt with above in discussing the application 

 of lime to peaty, clayey and light sandy soils. 



2. Chemical effects of lime on soils. — Lime acts directly as a plant 

 food, some plants requiring comparatively large quan- 

 tities; — one of its principal functions appears to be to 

 strengthen the woody portions of trees. 



The effect, however, of lime as a direct plant food is of minor 

 importance as compared with its indirect action on soils, due to its 

 action as a base. 



It acts indirectly by rendering available the dormant fertility of 

 all soils. It liberates potash from the insoluble silicates with which 

 it is combined. Quicklime or slaked lime is prefeiable to lime-stone 

 for this purpose. It also assists the decomposition of organic nitro- 

 genous matter, when not present in excessive quantity, and is thus 

 especially beneficial in this respect on peaty soils. 



It corrects soil acidity which is generally harmful to vegetation. 

 Many coarse grasses, sedges and other weeds which only flourish on 

 acid soils disappear after the application of lime. 



It also renders phosphoric acid available by liberating it from 

 its combination with iron and alumina with which phosphoric acid 

 must be usually combined in the laterite soils in this country. 



It is also essential after the application of repeated dressings of 

 other manures such as Ammonium sulphate, Kainit and Superphos- 

 phates, the accumulated effects of which are to produce acidity. Thus 

 in general the application of artificial manures necessitates a cor- 

 responding increase in the application of lime. 



Biological effects of Lime: — The biological effects of lime on 

 soils, as stated before, are intimately connected with the chemical 

 effects. 



It is essential to the successful action of nitrifying bacteria, to 

 combine with the nitric acid produced by these bacteria. It generally 

 assists other fermentative actions in the soil, since those which 

 are of benefit only occur in the presence of some base such as lime, 

 whereas deleterious fermentation changes occur in sour soils in which 

 nitrogen is actually liberated and escapes into the atmosphere. 



Another important function is its inimical action on a number of 

 fungoid root diseases, the particular instance in connection with the 

 cultivation of para rubber trees being its action on Fomes semitostus. 



