202 THE SYSTEM OF FARM-YARD MANURING. 



and tubers included) : and if clover still yields good 

 crops upon a soil wherein potatoes thrive but imper- 

 fectly, this is chiefly owing to the wider root-ramifica- 

 tion of the clover plant. There are scarcely any two 

 other plants which so clearly indicate the layers of the 

 soil assigned to them by nature, for the absorption of 

 their nutriment. 



If potatoes are planted in trenches two feet deep, 

 and if these are filled up in proportion as the plant 

 grows, so that at last the earth in the trench is on the 

 same level with the arable surface, it is always found 

 that the tubers are formed only in the topmost layer, 

 none at a greater depth, and not more in number than 

 if the seed-potatoes had been planted only 1-J- or 2 

 inches deep in the arable surface soil : and on gathering 

 the crop it is observed that the roots below the arable 

 surface have died away. 



"With clover, the case is reversed ; and although the 

 arable surface soil at Kotitz, for example, is decidedly 

 richer in substances nutritive for clover than that in 

 Cunnersdorf (yielding a potato crop higher by one- 

 eighth), this had no effect upon the clover, which 

 receives its principal nutriment from the deepest layers 

 of the soil. 



We now proceed to an analysis of the returns which 

 were obtained, in the Saxon experiments, by employing 

 farm-yard manure upon the plots of the same fields, 

 the crops of which in their unmanured state we have 

 just been considering. 



