6 STIRRING THE SOIL. [CHAP. I. 



earth. The second point, that of affording the 

 root abundance of nourishment, may also be 

 attained by pulverising the ground ; as pulveri- 

 sation, by admitting the air freely, and allowing 

 the rain to percolate slowly through the soil, 

 affords an equable supply of proper food to the 

 spongioles, without suffering the surplus water 

 to remain so long around the roots as to be in 

 danger of rotting them. 



These, then, are the reasons why it may be 

 laid down as a general rule, that all ground 

 should be stirred before seeds are sown in it ; 

 but there are other reasons which operate only 

 partially, and are yet almost as necessary to be 

 attended to. When manure is applied, the 

 ground is generally well dug, in order to mix 

 the manure intimately with the soil : and when 

 the soil appears worn out, that is, exhausted of 

 its nutritious properties, it is trenched ; that is, 

 the upper or surface soil is taken off by spade- 

 fuls and laid on one side, and the bottom or 

 sub-soil is taken out to a certain depth pre- 

 viously determined, and laid in another heap. 

 The surface soil is then thrown into the bottom 

 of the trench, and the subsoil laid on the sur- 

 face, and thus a completely new and fresh soil 

 is offered to the plants. Trenching is also use- 

 ful to land that has had lime applied to it, and 

 to sandy soils that have been mixed with clay ; 

 as both the lime and the clay have a tendency 

 to sink downwards, and to form layers below 

 the surface soil, which is thus deprived of the 

 benefit which it was expected to derive from the 

 mixture, till they are again brought to the sur- 

 face by trenching. The saline properties of a 



