34 An Account of the Soil [pt.i 



name and is called the subsoil. The dilference lies in 

 the fact that neither plant nor animal life has been able 

 to exert any great effect, so that the subsoil contains 

 very little more than the original mineral material. It 

 contains less organic matter than the surface soil, and 

 in consequence has not the satisfactory physical proper- 

 ties conferred thereby and it possesses less nutrient 

 plant material. Usuallj^ also it contains more clay and 

 this is present in the sticky rather than in the crumbly 

 form. Both causes combine to render the subsoil less 

 tractable than the surface soil, and on heavy soils it may 

 become so bad that it must on no account be brought 

 to the surface. Indeed many acres of land have been 

 ruined by deep steam ploughing which has buried the 

 surface soil and only left the plants with a sticky un- 

 kindly subsoil. An advantage of the one-way or turn- 

 wrest plough is that it does not, hke the ordinar}^ plough, 

 leave furrows of barren subsoil throughout the field be- 

 tween each of the lands. 



The following experiment has been started at Roth- 

 amsted and might advantageously be tried elsewhere. 

 Select some suitable site in the experimental field or 

 garden and construct therein two brick chambers each 

 20 inches deep and 7 ft. square, with cement floor and 

 Mning, making a way out for drainage -water (Fig. 12). 

 Fill both with subsoil obtained during excavations for 

 a building or dug specially. Leave one entirely alone 

 and observe the changes it undergoes: sow the other 

 with crops and observe their manner of growth. 



Plough Soles and Pans. At a depth of 4 or 5 inches 

 below the surface of the soil there is sometimes a hard 

 layer through which penetration is difficult. This is 

 called a plough-sole ; it is the result of persistent plough- 



