loOcT.. iQi^.J Relation of Lime to Soil Fertility. 619 



vr. 



IHl-: RliLATlOX OF LlMl-: 'JO SOIL FERTILIIV. 



By ] villi \\ . I'aiersoii, B.Sc. Ph.D., Experiiiientalist , and P. R. Scott, 

 Clnniist for Agriculture. 



A manure is a substance used to supply a necessary plant food to the 

 soil. Phosphoric acid is a necessary plant food which is often deficient 

 in soil, and superphosphate may lie employed to supply this. Super- 

 phosphate is thus a manure. 



Lime is also a necessary plant food. But in practice a soil never con- 

 tains too little lime to serve as plant food for the next crop. In the strict 

 .sense of the term, therefore, lime is not a manure. 



The beneficial action exerted by lime in a soil is indirect. Lime is a 

 strong base. An acid is a sour substance. When a .strong l)ase is added 

 to an acid, it combines with it, and the .sourness disappears. Most of the 

 improvements effected in soils bv lime are due to its basic character. Its 

 action is to keep the land from getting sour. 



Lime in Soil.s. 



I-ime exists in a soil in various forms, lait always comlnned with an 

 acid. It is combined with sulphuric acid in sulphate of lime (gypsum), 

 W'ith phosphoric acid in phosphate of lime (bones, super, &c.), and with 

 silicic acid in silicates of lime of various degrees of complexity. In all 

 these compounds the acids are strong, and they hold the lime firmly. In 

 sulphate, phosphates, and silicates of lime, the lime is held so firmly that 

 it is not available as a base. Gypsum or bones cannot remove soil acidity. 



Carbonate of lime is another form of lime existing in soils. It is a 

 compound of lime with carbonic acid. Carbonic acid is a weak acid, and 

 is also volatile, so that it is easily driven out from carbonate of lime. 

 When this happens the lime is available as a base. 



So far as the lime content of a soil is concerned, carbonate of lime is. 

 for most purposes, the only form that counts. It is valuable becau.se it is 

 easilv decomposed, thus vielding free lime on demand. If a soil has not 

 got a suitable supply of carbonate of lime, then liming is necessary. 



FoRM.S IN WHICH LiME MAY BE AppLIED. 



Lime may Ije applied to soils in various forms, viz., as free or hot 

 lime, as slaked lime, or as carbonate of lime (see Mr. Scott's article herein). 

 The value of lime in these forms lies in the fact that if not alreadv car- 

 bonate of lime, they are soon changed to carbonate by the carbonic acid 

 of the .soil. The .soil has then a supjilv of lime tit^d up as carbonate, but 

 available when required. 



l^FFECT Depending on Fineness ov Division. 

 ^^■hen carbonate of lime in the soil is decomposed to furnish available 

 lime, the action takes ijlace on the outside of the particles of carbonate 

 of lime. The larger these particles the smaller is the surface exposed 

 for the same weight of carbonate, and the slower, consequently, will it 

 act. The benefit derived from the presence of carbonate of lime in a soil 

 depends, therefore, not only upon the quantity present, but also upon its 

 fineness of division. 



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