PRINCIPLES OF TILLAGE. 121 



sioned by it, as we continued to cultivate a piece of ground 

 next to it in the usual manner. 



"7. I must further mention, as the last, but not less 

 important principle and cause of success, that each of the 

 manured fields has been brought to that point of fertility 

 in which it can yield the greatest produce ; so that with 

 less manure, it would not yield its full produce, and more 

 manure would cause the crops to lie down, even if the 

 year was not wet. The difficulty of being able to fix 

 this point, for every field and kind of crop, with certainty, 

 was removed by the now perfected geometrical method 

 by which, with the help of a scale formed on twenty years' 

 experience, the degree of productiveness may be marked, 

 in which the field has been left in the last crops ; i. e., 

 seldom below 100 degrees, which denotes a field capable 

 of yielding 24.02 bushels of wheat per acre, and below 

 which it is not advisable to let a field sink." 



Jethro Tull and his disciples maintained, that the great 

 secret of inducing fertihty, consisted in minutely dividing 

 and pulverizing the soil by culture ; and John Taylor, 

 the Arator of Virginia, and an excellent practical as well 

 as scientific farmer, considered the atmosphere as the 

 great store-house for vegetable food, where it exists in a 

 gaseous form. The good tillage we advocate embraces 

 all the advantages of Tull's and Taylor's theories, with- 

 out lessening the importance which we attach to barn-yard 

 manure. 



The deep ploughing of dry land, or the breaking up 

 and stirring of the subsoil, promotes fertility, by increas- 

 ing the power of the land to absorb water by cohesive 

 attraction. " The power of soils to absorb water from 

 air," says Davy, " is much connected with fertility. This 

 power depends in a great measure upon the state of di- 

 vision of its parts ; the more divided they are, the greater 

 their absorbent power. When this power is great, the 

 plant is supplied with moisture in dry seasons ; and the 

 effect of evaporation in the day is counteracted by the 

 absorption of aqueous vapors from the atmosphere, by 

 the interior parts of the soil, during the day, and by both 

 the exterior and interior during the night," The soil im- 



11 XV. 



