17^ ON FALLOWING. 



•' tuents from the soil, or adding others, or 

 ** 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, Twmely^ fallo'wing, 



" 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 

 ** with advantage, but is certainly unprofitable 

 ** as part of a general system of husbandry. 



" It has been supposed by some waiters, 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 j some 

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

 " are capable of attracting carbonic acid, are 

 " always saturated wdth 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 



