o 



BREAKING UP OLD GRASS LAND 119 



of assimilating ammonia, nitrogen, and other plant foods more 

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

 grated condition, when the staple 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 

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

 and, under the high temperature, attacks the silicates, sets free 

 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. 1 An admixture of lime with the ashes 

 greatly augments their value for clay soils. 



Burning also destroys the noxious forms of vegetation, and 

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

 larvse 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 turnip seeds have plenty of time to 

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

 troublesome on newly-burned land. 



1 The following is Sir JEL 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 



Oxide of iron ............ 15 



Insoluble earthy matter . . . ... 82 



200 



