PARING AND BURNING 221 



the formation of new plants. The ashes, then, of 

 the weeds consumed in the process of paring and 

 burning will be very useful to the plants about to 

 be raised on the land that has been burnt over. By 

 the burning, however, it is impossible to turn to 

 account all that the weeds contained: what escapes 

 in the form of smoke is so much lost. Hence care 

 should be taken not to carry combustion too far. 

 In this connection the calcined clay renders still 

 another service. By becoming porous through cal- 

 cination its nature is altered so that it can absorb 

 and retain the gaseous products of combustion and 

 thus save just so much waste. But if a soil lacks 

 clay, paring and burning are harmful, and it is bet- 

 ter simply to turn the weeds under, whereupon they 

 will be converted into mold instead of being dissi- 

 pated in the atmosphere as smoke. 



"Ashes other than those resulting from paring 

 and burning are also used as an agricultural fer- 

 tilizer, though they are rarely put to this use just 

 as they are, because the contained potash, a highly 

 valuable substance, is first extracted by leaching. 

 After this process the ashes are called buck-ashes. 

 They contain silica and also carbonate and phos- 

 phate of lime, all in a condition most favorable for 

 assimilation by plants. Of less strength than ordi- 

 nary ashes, leached ashes nevertheless produce good 

 results, especially on clayey soil. Coal ashes, too, 

 it should be added, serve to lighten a heavy soil 

 since they contain a large proportion of calcined 

 clay. 



