THEORY AND PKACTICE. 105 



rather more than half a bushel of "Tail," to the 

 acre. 



How completely the Lime had done its work, in 

 both capacities, may be judged of from the fact that 

 on a couple of acres which I retained expressly for 

 the after experiment, and sowed with Beans and 

 then with Oats, unmanured, the two succeeding 

 years, the return exhibited an utter exhaustion of 

 the productive powers of the soil, to an extent that 

 I could hardly have believed, without experimental 

 proof. 



Though it cannot be desirable to see the practice 

 of bare fallows extended ; for it exists too much 

 already upon many soils where it might be with 

 every advantage substituted by green-crops ; it must 

 yet be borne in mind that it is not in the mechanical 

 structure alone that heavy soils differ from light 

 soils ; their chemical difference^ which is quite as 

 great, lies in that essential particular that the clay 

 soil is naturally richer in the mineral constituents 

 required by your crops. Potash, Soda, and Phos- 

 phorus, which you must supply to a light soil before 

 you sow it, you have only to develop in a clay soil 

 by deep and frequent stirring, and submitting to the 

 oxidation of the atmosphere. The green-crop, with 



its carbon-obtaining leaves, will no doubt supply 

 5* 



