On Paring and Burning. 15 



and at the same time be benefited by the organic portion of the 

 vegetable remains of former crops ? In reply to this question, it 

 may be stated that couch and the roots of clover, &c., do not 

 readily lose their vitality nor decompose with sufficient rapidity 

 to admit of this plan being carried out in the cultivation of root- 

 crops, for which paring and burning is specially adapted. In 

 fresh roots and other vegetable remains, the saline inorganic con- 

 stituents, found in their ashes, are so firmly united with organic 

 constituents, that it is impossible to dissolve by means of water 

 any appreciable quantity even of such soluble combinations as 

 alkaline salts. By the decay of vegetable matters, their mineral 

 constituents are gradually rendered soluble, and by the rapid 

 destruction by fire their mineral matters are at once made 

 soluble and rendered available to the immediate use of plants. 

 These saline mineral constituents, in such a soluble state, act as 

 powerful manures ; and hence it is that paring and burning pro- 

 duces an immediate effect upon plants which, like all quick- 

 growing plants, require, so to say, ready-made or soluble mineral 

 food. 



The excess of undecomposed organic matters in soils, moreover, 

 is decidedly injurious to vegetation. Peaty soils furnish familiar 

 examples of this. Soils upon which paring and burning is prac- 

 tised with the most benefit contain often much and always a fair 

 proportion of clay ; they are impervious and compact in texture, 

 and for this reason do not readily admit air. The roots, stems, 

 and other vegetable matters remain, therefore, buried in the ground 

 for years without undergoing decomposition, or that preparation 

 which we have just seen is so necessary to their yielding soluble 

 fertilizing substances to a quick-growing crop. Thus the destruc- 

 tion by fire of the organic remains in heavy soils, far from doing 

 any harm, is the most available and economical means of pre- 

 venting their undue accumulation. The fire, I would observe, in 

 concluding this part of the subject, destroys insects, their eggs 

 and larvae, as well as the seeds of weeds, bits of underground 

 stems, which, like the knots of couch, are so apt to vegetate again, 

 and which, therefore, cannot be got rid of so effectually as by 

 burning. In short, nothing cleans land so thoroughly as paring 

 and burning. 



2. Action of Heat on the Inorganic or Mineral Matters of the 



Soil. 



The heat generated during the combustion of the organic re- 

 mains affects the mineral or soil constituents, properly so called, 

 at least in part, producing in them changes which are partly of a 

 mechanical, partly of a chemical kind. 



In a former contribution to the Royal Agricultural Society's 

 Journal I have described, in detail, the nature of the physical 



