156 THE PRACTICE OF THE 



fure, as appears from his letter above quoted, 

 where he fays, " The repeated ftirrings not 

 ** only improve the foil by keeping it in a 

 ** loofe flate, proper to be penetrated by the 

 c roots and fibres of plants, which are thus 

 ** enabled to draw their nourimment from it : 

 " but they expofe every particle, in its turn, 

 * to the influence of the atmofphere ; and 

 " procure an inexhauftible fupply of food for 

 " the purpofes of vegetation.*' This is found 

 to be true from experience : and giving this 

 land but three horfe-hoeings, inftead of four, 

 appears to be the reafon that this gentleman 

 thought, that twelve bufhels of wheat on an 

 acre is about the medium quantity to be ob- 

 tained from moderately fertile ground without 

 dung ; whereas we have feen, that Mr. Tull 

 obtained a great deal more; and that he, Mr. 

 Dean and Mr. Craik, obtained near as good 

 crops, in the way of drilling and hoeing, as 

 was ufually obtained in the common or broad- 

 caft Hufbandry. 



One caufe of the drilled crops falling fo 

 much fhort of the broad-cad has been, that 

 the experimenters have depended too much on 

 the finenefs or pulverization of their land ; 

 which is without doubt neceflary, that the 

 roots may freely penetrate and extend in it; but 

 pulverizing does not of itfelf enrich land : it 

 rather prepares it to be exhaufted, by the roots 

 of plants extending more freely therein ; 

 whereas expofure brings additional riches to 



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the 



