THE CHEMISTRY OF THE SOIL. 91 



Chemical Action of Lime. 



Apart from the above mechanical property «>t' lime in improving the texture 



of the soil, it has also a chemical action, and though this is not thoroughly 

 understood, it may be classed under the following headings : — 



Firstly, it neutralises the acids sometimes present in soils. Sour soils 

 in particular, contain free acids present in such quantities as to be 

 injurious to plant life, and such soils are "sweetened" by the 

 application of lime — that is to say, the free huinic and similar acids 

 are neutralised. 



Secondly, it at lacks the inert organic matters in the soil and promotes 

 fermentation — one of the most active agents in the production of 

 available plant-food. It is, of course, possible to have too much of 

 a good thing, and an excessive dressing of lime would .tend to burn 

 up the vegetable matter of the soil, and do as much harm as good ; 

 but in the moderate dressings recommended, it will be found 

 beneficial even on land which has recently been green-manured. It 

 must not be forgotten, however, that the action due to cauBtic lime 

 soon ceases, for it is very rapidly converted into carbonate of lime 

 within the soil, which has no such action on organic matter. 



Thirdly, it attacks the insoluble mineral constituents of the soil to some 

 extent. Phosphoric, acid enters into combination with lime, and 

 is in this form more readily utilised by the plant than in its insoluble 

 combinations with iron and alumina, with which it is associated 

 in the soil. Owing to the tendency of lime to burn up a portion 

 of the organic matter, its benefit is more marked on soils rich in 

 organic matter. 



Fourthly, carbonate of lime (into which we have seen the lime is soon 

 converted in the soil) is beneficial, if not necessary, to the process 

 of nitrification, the peculiar ferment action by which the inert soil- 

 nitrogen is converted into nitrates. 



Fifthly, whilst it promotes certain ferment action, such as the above, it 

 hinders the active growth of many fungoid diseases like rust and 

 smut, and is said to be often a cure for such diseases. 



Methods of Application. 



1 Lime may be applied in two ways — either as ground lime or freshly slaked. 

 As ground burnt-lime, it is applied at the rate of 5 to 6 cwt. per acre in a 

 manure-distributor and lightly scattered over the surface. If freshly-slaked 

 lime is used it is applied in somewhat larger quantities up to \ ton per acre, 

 or even more in the case of very stiff clays. The heavy dressings once 

 employed are found to be less beneficial than smaller applications more 

 frequently applied. 



Liming with freshly-slaked lime is best carried out as follows: — The quick- 

 lime (stone-lime) is broken up into small lumps and placed in heaps about 

 the field covered with moist loam. It is left exposed to the air and moisture 

 until it begins to crumble to powder. As soon as this happens the heaps are 

 scattered with a shovel as evenly as possible over the surface of the field, and 

 harrowed or ploughed in very lightly. Liming is most effectively done in the 

 autumn or winter, but whenever it is done the land should be left alone for 

 two or three weeks after the application, and no seed sown nor any manures 

 (especially such as contain nitrogen or superphosphate) used during that 

 period. 



