no 



THE BOOK OF NATURE STUDY 



K 



over. Next, the top spit of the rectangle CEFD, is dug out and 

 transferred to rectangle ACDB, the second spit of CEFD is then 

 dug over. This series of operations is repeated on successive 

 rectangles until GH is reached, when the top spit of ACDE is 

 used to fill up the rectangle GHLK. The effect of the operation 

 thus is that the soil has been thoroughly stirred to two spades' 

 depth, but no subsoil has been brought to the surface. The 

 reason for not bringing the subsoil to the surface is that it is 

 frequently incompletely aerated, and not suitable for a seed 

 A B bed. Where, how- 

 ever, a garden has 

 o been established 

 some years it will 

 F be an advantage to 

 deepen the soil, as 

 distinct from the 

 subsoil, by bring- 

 ing the second 

 spade's depth to 

 the surface. 



In the process 

 of digging the soil 

 is loosened so as to 

 permit the plant 

 roots to forage 

 freely throughout 

 the soil which is 



H 



FIG. 52. Arrangement of ground for bastard trenching. 



within their reach. This is specially important in the early 

 stages of growth when any circumstance which tends to check 

 the growth of the plant has a particularly harmful effect. When 

 the plant is thoroughly established in the soil it is able, and in 

 fact does, send down its roots far below the level reached by 

 spade cultivation. In the process of digging, moreover, atmos- 

 pheric oxygen is introduced into the soil spaces, and 

 provision is thus made for the supply of oxygen to the roots, 

 without which they would die. Oxygen is required too for the 

 bacteria in the soil, which in a number of ways are necessary 

 for fertility. Any substances not fully oxidised, as, for example, 



