128 PBEMANENT AND TEMPORAEY PASTUEES. 



rapidly than before. Fire reduces clay to a friable, disinte- 

 grated 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 transform some of the mineral 

 elements from an insoluble to a soluble state. For instance, 

 as the soil probably contains various compounds of siUcates 

 and of Ume, the lime becomes hberated 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 hberation 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 soU which are of material advantage 

 to the plant-hfe 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 hme with the ashes greatly augments their value 

 for clay soUs. 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 



Carbonate of lime ........... 80 



Sulphate of lime, or gypsum 11 



Charcoal 9 



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



Glide of iron 15 



Insoluble earthy matter 82 



200 



