CULTIVATION. 29 



derived from 5 samples only. . . . There are reasons to 

 suppose that this result is too low. Furthermore it is 

 not improbable that tobacco loses nitrogen during the 

 curing process." 



The advantages of artificial manuring have been made 

 manifest in all branches of agriculture, and there is no 

 doubt that the nitrogenous qualities of farmyard dung 

 may be replaced by soda nitrate, ammonia sulphate, &c., 

 only it must be remembered that these have not nearly 

 the lasting effect of dung, the latter liberating its am- 

 monia but slowly. Indeed " when a soil has been heavily 

 dunged for a term of years, it accumulates a large quantity 

 of nitrogen, which is comparatively inert and therefore 

 nearly useless to crops. Quicklime assists to convert this 

 nitrogen into the active forms of ammonia or nitrates," 

 hence Prof. Johnson's suggestion that an " application of 

 lime may sometimes be advantageously substituted for one 

 of stable manure. In fact, it is not improbable that 

 moderate doses of lime might be turned under with stable 

 manure or green crops, with the efiect of exalting the 

 action of these fertilizers, and obtaining from them a 

 larger return of nitrogenous plant food. Lime, however, 

 gives effect to the nitrogen of the soil by causing the 

 destruction of the organic matters — humus — in which this 

 nitrogen lies in an inactive state. These organic matters 

 have themselves a value independent of their nitrogen, 

 which must be taken account of, and therefore the use of 

 lime must be undertaken cautiously, and with an intelli- 

 gent comprehension of the various effects which it may 

 produce." 



Rotation. — A proper rotation of crops is particularly 



