ON FALLOWING. 



u tuents from the soil, or adding others, of 

 " changing their nature. But there is an opera- 

 " tion of very ancient practice still much em- 

 " ployed, in which the soil is exposed to the 

 " air, and submitted to processes WHICH ARE 

 " PURELY MECHANICAL, namely, fallowing. 



" The benefits arising from fallowing have 

 " been much overrated ; a summer fallow, or a 

 " clean fallow, may be sometimes necessary in 

 " lands overgrown with weeds, particularly if 

 " they are lands which cannot be pared and burnt 

 4< with advantage, but is certainly unprofitable 

 " as part of a general system of husbandly. 



" It has been supposed by some writers, that 

 " certain principles necessary to fertility are de- 

 " rived from the atmosphere, which are ex- 

 " hausted by a succession of crops, and that these 

 " are again supplied during the repose of theland, 

 " and the exposure of the pulverised soil to the 

 " influence of the air ; but this in truth is not the 

 " case. The earths commonly found in soils 

 " cannot be combined with more oxygene ; some 

 " of them unite to azote, and such of them as 

 " are capable of attracting carbonic acid, are 

 " always saturated with it on those soils in which 

 " the practice of fallowing is adopted. The vague 

 " ancient opinion of the use of nitre, and of 

 " nitrous salts, in vegetation, seems to have been 



