THE PRINCIPLES OF CULTIVATION 219 



the surface. There is a popular quasi-moral idea that the good 

 soil lies below, and that a little hardy spade work and deep 

 ploughing to bring it to the top will do wonders towards restor- 

 ing and enriching the land. In the surface soil, however, rest 

 the sources of fertility the humus, which is the chief store of 

 plant food, and the bacteria which prepare it for the plant. If 

 they are buried and so rendered unavailable, years of work and 

 manuring may be needed to bring the subsoil into condition, 

 and store it with humus and bacteria. On clay land in par- 

 ticular the subsoils are harsh and infertile, and may even contain 

 substances injurious to growth. It is good to loosen and break 

 up the subsoil so as to let in the air and destroy any pans just 

 below the surface, thus rendering it easier for the roots of vegeta- 

 tion to get down deeply. Valuable, however, as a deep soil is, 

 it should be deepened very gradually by setting the plough only 

 half an inch or so lower year by year. For the same reasons, while 

 it is desirable that a garden should be trenched over deeply, so as 

 to extend the layer available for roots, in all cases the surface soil 

 should be restored to its old position as the top layer. Subsoiling 

 or trenching should be done as early as possible, to give the earth 

 time to settle down again ; otherwise, if the subsoil is left open, 

 vegetation will suffer from drought, because the loose texture and 

 the many gaps break the connection with the subsoil water and 

 hinder its capillary rise to the roots of the crop. 



The year's round of cultivation begins, then, with digging or 

 ploughing before the winter, by which means the alternate freezings 

 and thawings the soil experiences will not only crumble down the 

 clods into a natural fine tilth, but will also draw the finest clay 

 particles together and give the soil a better texture. At the same 

 time, the rough surface retains more of the winter rainfall, which 

 is absorbed and works down into the subsoil instead of running 

 off, as much of it does when the land is left hard and trampled by 

 the removal of the last crop. Even in Britain, where we may seem 

 to have rainfall enough all the year round, it is yet desirable to 

 conserve as much as possible for the summer crops, provided 

 that we can get it down into the subsoil and leave the soil proper 

 in a reasonably dry condition. Except in the wettest years and 

 situations, our crops are more often checked and reduced by a 



