CH. v] Improvement of Subsoil 91 



soil, and in designing the necessary cultural operations 

 it is necessary to bear in mind the distinctions already 

 set out (Chapter II) between the surface and the subsoil, 

 viz., the presence in the subsoil of less food, less organic 

 matter and less air than in the surface soil, and the 

 presence of more clay, which is likely to be in the 

 undesirable sticky state. 



The improvement of the subsoil is not commonly 

 attempted in farm practice excepting only on arable 

 soils where a plough-sole or a pan occurs near the sur- 

 face; recourse is then had to subsoiling, and often with 

 considerable success. The operation is not necessary 

 oftener than once in four or five years, and it can well 

 be done as part of the preparation for the root crop. 



At Rothamsted subsoiling increased the yield of the 

 potato crop by about half a ton per acre, but no effect was 

 visible on the subsequent crops . Striking effects have been 

 produced in Essex. In Southern Illinois it did not benefit 

 the cereal crops : if anythingtherewasaslightdepression^. 



In fruit growing districts attempts have recently been 

 made to break the hard layer by means of explosives: 

 the method is said to be effective in South Africa, but 

 it was unsuccessful in Scotland. 



In market gardening and horticulture it is common 

 to trench the land with the object of making the subsoil 

 more like the surface soil. Sixty years ago it was thought 

 that the subsoil was reaUy the virgin soil, rich in stores 

 of food that only needed liberating by the action of 

 frost. Sixty years of experiment have shown that this 

 is not correct; the subsoil is really very poor in plant 

 nutrients, and nothing whatever is gained by bringing 

 it to the surface. Considered as a manure it is des- 



1 Rothamsted Ept. 1915-17, p. 68. Illinois Expt. Station Bull. 181, 1915. 



