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Lime, as applied to the soil, is in three different states : Car- 

 bonate of lime, a compound of lime and carbonic acid, such 

 as limestone or chalk, and sometimes called mild lime. 

 Also as burnt or caustic lime obtained by burning the 

 carbonate to drive off the carbonic acid, and sometimes called 

 quicklime. As gypsum, a compound of lime and sulphuric 

 acid obtained as a by-product in several manufactures ; having a 

 manurial value differing from the carbonate and the caustic lime. 

 The mechanical actions of the carbonate and the caustic lime are 

 much the same, only the caustic is much quicker than the carbonate. 



Heavy or clayey soils when they get wet puddle and become 

 sticky, so that they are difficult to handle. This puddling is owing 

 to the particles of the soil being in a very fine state, and getting into 

 what may be called a semi-state of suspension. The clay when it 

 dries contracts and gets caked or packed, which makes it difficult 

 to work. The effect of lime on such a soil is to precipitate or 

 coagulate the fine particles of clay, something in the manner in 

 which sewage is purified by lime, which causes the suspended 

 solid matter to be precipitated and leaving the water clear. The soil 

 is also made more open and pervious, thereby allowing the water to 

 drain away. It also makes the soil more friable and easy to work. 

 The lime does not contract when it gets dry, as the clay does, th 

 making the soil more porous, friable and easy to break up. 



Lime, while thus acting on clayey soils, curiously enough, has a 

 reverse action on light sandy soils. It assists to bind the soil, 

 making it more retentive of moisture and giving it a great 

 capacity for absorbing moisture from a depth by increasing i 

 capillary power. 



When caustic or burnt lime is used, it should be first slacked 

 by allowing it to absorb moisture or pouring watt r over it. Caustic 

 lime is best for clayey and peaty soils and soils rich in organic 

 matter. Th,e rules are : 



For heavy soils use caustic lime. 



For light soils use carbonate of lime. 



For soils rich in organic matter use caustic lime. 



For soils poor in organic matter use carbonate of lime. 



CHKMICAL ACTION OF LIMI:. 



Lime acts more powerfully chemically than mechanically. It 

 acts directly as a plant food. It acts by liberating potash from its 

 insoluble and inert compounds, and bringing it into a state fit for 

 the plants to absorb. It also promotes the formation of hydrated 

 double silicates, which lix or retain in the soil the ammonia and 

 potash supplied by manure and in a state lit for the plants to 

 absorb them. Soils rich in organic matter, such as peaty 

 soil or rich nr-adows, generally give rise to an excessive amount 

 of organic acids, which cause sourness in the soil and act 

 as a poison upon plants. The herbage that grows on these is 



