118 PEEMANENT AND TEMPOEAEY PASTUEES. 



reduces clay to a friable, disintegrated condition, which readily 

 absorbs fertilising matter. The late Dr. Voelcker conclusively 

 proved this to be the case, and that the effect of heat is to trans- 

 form some of the mineral elements from an insoluble to a soluble 

 state. For instance, as the soil probably contains various com- 

 pounds of silicates and of lime, the lime becomes liberated by the 

 heat, and, under the high temperature, attacks the silicates, 

 liberates part of the potash from its insoluble compound, and 

 converts it into soluble plant food. This liberation of potash has 

 probably more to do with the success of burning than any other 

 result consequent upon it. Thus the action of fire effects chemical 

 and physical changes in the soil which are of material advantage 

 to the plant-life which follows. Burning has really very much 

 the same effect, but in a more intense degree, that liming has in 

 sweetening the soil, and in setting free quantities of inorganic 

 matter which were previously in a locked-up condition.^ An 

 admixture of lime with the ashes greatly augments their value 

 for clay soils. Burning also destroys the noxious forms of vege- 

 tation, and the land is freed from bots and grubs, and other 

 destructive larvae of insects. 



It is usual to take at least one crop of roots immediately 

 after burning, and in such a case a mis-plant is rarely known. 

 The ashes absorb so much moisture from the atmosphere, and 

 give it up so slowly, that the turnip seeds have plenty of time 

 to germinate, however great the heat. Even the fly is seldom 

 troublesome on newly-burnt land. 



' The following is Sir H. Davy's analysis of the ash of burnt turf: — 



Parts 



Oarhonate of lime 80 



Sulphate of lime, or gypsum 11 



Charcoal 9 



Saline matter, principally sulphate of potash and muriate of magnesia . 3 



Oxide of iron 15 



Insoluble earthy matter 82 



200 



