TRENCHING. 



514 



TRENCHING. 



trellis is made, and its dimensions, both 

 closed and open, and its price per piece : 



The above prices may vary slightly with 

 different makers ; but as far as calculating 

 the cost of covering any given area goes, 

 they will be found to be sufficiently 

 approximate. 



Trenching. 



Next in importance to drainage and 

 burning is the introduction into the soil of 

 atmospheric air, which is a combination of 

 oxygen and hydrogen one of the objects 

 of drainage being to admit oxygen, with 

 the other constituents of atmospheric air, 

 into the soil. We are now brought on to 

 a consideration of digging as the third and 

 best known, because most frequently prac- 

 tised, of the three great mechanical means 

 by which natural soils are prepared and 

 brought into cultivation. The admission 

 of atmospheric air, which is promoted in 

 the first place by draining, is facilitated by 

 the deep trenching which usually follows 

 the thorough drainage of a garden ground. 

 The immediate object of trenching is to 

 deepen the soil, and prepare the subsoil to 

 nourish the fibres of deep-rooting plants. 

 The operation is commenced by throwing 



out the top spit to a convenient breadth for 

 the workman, and wheeling it to the 

 farther end of the bed or quarter ; the 

 second spit is treated in the same manner 

 if the trenching is to be three spades deep. 

 This done, the bottom of the trench is dug 

 up as roughly as possible, so that it is left 

 level. The top spit of a second portion of 

 the ground is now removed and placed 

 alongside the first, and the second spit of 

 this portion is dug up and placed roughly 



FIG. I. PLAN OF GROUND MARKED FOR 

 TRENCHING. 



over the first trench. The first spit of a 

 third portion is now removed and placed 

 in as large masses as possible over the first 

 trench : the bottom of the second trench is 

 now dug up in the same manner as the 

 first, and so on till the whole is finished. 



How Done. To render the operation 

 of trenching three spades deep fully intelli- 

 gible, it may be as well to make the 

 description that has just been given yet 

 more clear by reference to a diagram. 

 Thus, in Fig. I, a plan of the ground to 

 be trenched is shown divided into trenches, 

 A, B, c, &c., of convenient width, say 12 



