SOIL ANALYSIS AND ITS INTERPRETATION 139 



light soil, but it must be cool and moist. The Nutfield soil (Table LIV.) 

 fulfils these conditions ; it is on a slope facing northwards not very far 

 above a stream, and, therefore, does not quickly dry out, hence it is very 

 good for main crop potatoes. The Tolworth soil, on the other hand, 

 although similar in composition, is so placed that it quickly dries and is 

 of much less value. Some of the potato soils of Dunbar, analysed by 

 S. F. Ashby (8), have all the appearance of soils readily drying out, but 

 in their cool climate this property does not show itself to an injurious 

 extent. 



TABLE LIV. WATER-SUPPLY AND INTERPRETATION OF MECHANICAL ANALYSIS. 



Effect of Underground Water. When the underground water is 

 near the surface, but sufficiently far below to allow of proper root 

 development, the most important property of the soil becomes its 

 power of lifting the water by surface action up to the roots. The silt 

 and sands are in such cases the useful constituents, the clay and fine 

 silt being less necessary. The Weybridge soil (Table LV.), at about 

 3 feet below its surface, has a current of underground water which is 

 brought to the roots by the fine and coarse sand. It therefore grows 

 excellent wheat crops. The Bagshot sands, however, although similar 

 in physical type, have in general no such water-supplies and are sterile 

 because they lack the clay which, in their circumstances, could alone 

 confer an adequate power of holding water from one shower to the next. 

 TABLE LV. UNDERGROUND WATER AND MECHANICAL ANALYSIS. 



IO 



